119
Synthesis of MgO nanostructure thin films via electrodeposition method for gas
sensing applications
N. Lal1,3, A. Kumar2, K. Chawla1,4, S. Sharma1,5 and C. Lal1,2*
1Department of Physics, University of Rajasthan, Jaipur, Rajasthan 302004, India
2Centre for Non-Conventional Energy Resources, University of Rajasthan, Rajasthan 302004, India
3Govt. Girls College, Jhunjhunu, Rajasthan 333001, India
4Govt. College, Pratapgarh, Rajasthan 312605, India
5Govt. College, Jhunjhunu, Rajasthan 333001, India
Abstract
Magnesium oxide has long been intriguing due to several significant phenomena, including wide
laser emission, spin electron reflectivity, and defect-induced magnetism. MgO nanostructures
have a variety of applications, from spintronics to wastewater treatment, depending on their size
and shape. Mg is sensitive material for hydrogen and forms MgH2, so we used Mg/MgO as a
sensor to sense hydrogen gas in the present work. Magnesium oxide thin films were synthesized
by electrodeposition technique using magnesium nitrate salt. XRD results suggested that the
deposited thin films have a face-centered cubic structure. X-ray photoelectron spectroscopy was
used to detect the elemental composition and chemical state with the general electronic structure
of the sample. The morphology and growth of deposited nanostructure with elemental mapping of
the thin film were investigated by SEM-EDS. The UV-visible analysis shows the calculated band
gap for MgO thin filmwas 4.16 eV which is in the ultraviolet region. The I-V characteristics have
been studied to find out the effect of hydrogenation on the synthesized MgO nanostructure and the
sensitivity responseof about 31%. It is quiteevident that MgO nanostructure may be used for gas
sensing applications (such as H2 gas).
Keywords: Magnesium oxide; Nanostructure; Electro-deposition; Electronic structure;
Hydrogenation
*Corresponding author’s e-mail: clsaini52@gmail.com; clsaini52@uniraj.ac.in
Available online at www.banglajol.info
Bangladesh J. Sci. Ind. Res. 58(2), 119-128, 2023
Introduction
Nanostructure magnesium oxide thin films have drawn
considerable attention because of their specific physical,
chemical, and optical properties. Magnesium oxide, an
insulating ionic simple oxide, crystallizes in bulk in the rock
salt structure. The synthesized metal oxides with proper phase
and structures have great interest in order to realize their
specific properties that not only depend on their chemical
composition but also on their shape,size, phase, crystal, and
electronic structure as well as absorption ability, catalytic
ability, surface reaction activity (Lan et al. 2011; Chatterjee et
al. 2009; Bhatte et al. 2012). Since the discovery of carbon
nanotubes, researchers have focused intensely on developing
nanostructures made of other materials in a variety of domains
(Huang et al. 2013; Yourdkhani and Caruntu 2011). Nano-
cubes, nanorods, and nanoflowers are the most coveted types of
nanostructures, in addition to nanoparticles and thin films.For
many oxide systems, these kinds of nanostructures and their
advantages are being examined (Wang et al. 2016; Weber et al.
2008). Magnesium oxide is a non-toxic, non-corrosive material
that is rapidly utilized in composite materials for space flight,
medicine, toxic waste treatment, and catalysis (Zou et al. 2008;
Jia et al. 2013; Wang and Xue 2006). A variety of electrochemi-
cal biosensors have recently been created employing nanoscale
MgO material as a precise and sensitive tool for analytical
application and diagnostic analysis (Ma et al. 2011; Li et al.
2009). Magnesium oxide has strong thermal conductivity as
well as an excellent electrical insulator so valuable as
thermocouples and heating systems components.
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Received: 29 January 2023
Revised: 21 May 2023
Accepted: 21 May 2023
Short Communication
Synthesis of MgO nanostructure thin films via electrodeposition method 58(2) 2023120
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Fig. 1: (a) Schematic block diagram (b) Electrodeposition working setup and (c) furnace for heating
Lal, Kumar, Chawla, Sharma and Lal 121
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Fig. 2. XRD spectrum (a) bare ITO (b) synthesized
Mg(OH)2 and (c) MgO thin film
Mg(NO3)2 → Mg
2+ + 2NO3
– (i)
H2O + 2e
- → H2 + 2OH
- (ii)
Mg2+ + 2OH- → Mg(OH)2 (iii)
Mg(OH)2→ MgO + H2O (iv)
Dehydration of Mg(OH)2
produces MgO nanostructures
onto ITO substrate.
Synthesis of MgO nanostructure thin films via electrodeposition method 58(2) 2023122
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Fig. 3. (a) Survey scan of deposited MgO nanostructure and core level of (b) Mg 1s (c) O 1s (d) Mg 2p
Lal, Kumar, Chawla, Sharma and Lal 123
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Table 1. B.E. for different elements available in MgO
nanostructure thin film
Elemental composition Binding Energy (eV)
Mg 1s 1302.8
O KLL 976.23
O 1s 531.64
Mg KLL 304.64
C 1s 285.41
Mg 2s 86.98
Mg 2p 48.21 (αhν)2 = C(hν - Eg) (vi)
Fig. 4. Micrograph of synthesized MgO with elemental mapping
Synthesis of MgO nanostructure thin films via electrodeposition method 58(2) 2023124
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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(c) derivative of absorbance versus energy (d) Transmittance spectrum
Fig. 6. FTIR spectra of synthesized MgO nanostructure
Lal, Kumar, Chawla, Sharma and Lal 125
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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MgO nanostructure thin film (In vacuum and with
Hydrogen)
Fig. 8. Experimental gas sensitivity measurementsetup
(a) Schematic block diagram (b) PCT/PCI setup
vii
Synthesis of MgO nanostructure thin films via electrodeposition method126 58(2) 2023
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Lal, Kumar, Chawla, Sharma and Lal 127
MgO was known asa low-cost and environment-friendly
material that has so many applications like bioresorbable
materials that dissolve in biofluids (Huang, 2018), drug
delivery (Ravaei et al. 2019), electrodes in pharmaceuticals
and human fluids (Kairya et al. 2017), resistive switching
(Guo et al. 2019), luminescence (Nikiforov et al. 2016),
photo-catalytic properties (Demirci et al. 2015) and ultra-vi-
olet (UV) photodetector (Zhou et al. 2019). MgO nanostruc-
tures have also been reported to exhibit thermoluminescence
(Abramishvili et al. 2011), radioluminescence (Skvortsova
and Trinkler 2009), and electroluminescence (Benia et al.
2007). Thin metal oxide films that are electrically insulating
are a crucial component of many different technologies, so
magnesium oxide (MgO) has received a lot of attention for
applicationssuch as spintronic devices since it has a material
with a reasonably high dielectric constant. Under the
influence of UV light, methyl orange, and methylene blue
dyes were degraded using the photocatalytic activity of MgO
nanoparticles (Mageshwari et al. 2013). Hydrogen storage
properties of Mg/Ti bilayer thin films were reported (Jangid
et al. 2021) at a different hydrogen pressure of 15 to 45 psi to
realize the effect of hydrogenation. Hydrogen is the lightest
element in the universe, which is typical to detect and magne-
sium is very sensitive to hydrogen in comparison to other
metals. (Chawla et al. 2022). Although magnesium (Mg) is
one of the better aspects for absorbing hydrogen, difficult to
use this material for mobile applications due to its slow
dynamics and need for high temperatures during dehydroge-
nation. Due to its extremely large reversible hydrogen capac-
ity, magnesium hydride is particularly intriguing (Jangid et
al. 2021). The present work reports the electrical behaviour
and sensitivity of magnesium oxide (MgO) asa sensor to
sense H2 gas. In a similar work dip-coated CuO thin films
were used to investigate the gas-sensing response of CO2
vapor in air at room temperature and reported that the physi-
cal qualities that can be altered have a lot of potential for CO2
gas-sensing applications. (Musa et al. 2021).
For the synthesis of thin films with nanostructures, an easy,
affordable, and solution-based hybrid method is
electro-deposition. MgO nanostructures have been grown
successfully from an aqueous solution of magnesium nitrate
Mg(NO3)2 using the electrodeposition method (Taleatu et al.
2014). The deposition procedure can be applied to a variety
of conductive substrates, including polymers, semiconduc-
tors and ITO-coated glass. Indium tin oxide (ITO) is the most
widely used substrate because of its outstanding transparency
to visible light and high electric conductivity (Muchuweni et
al. 2017). In the present work, magnesium oxide nanostruc-
ture thin film deposited by electrode position technique using
magnesium nitrate solution. To synthesize MgO nanostruc-
ture, a variety of experimental procedures have been
proposed, including reactive sputtering (Choi and Kim
2004), metal-organic molecular beam epitaxy (Niu et al.
2000), chemical vapor deposition (Carta et al. 2007), sol-gel
(Zulkefle et al. 2011), and pulsed laser deposition (Kaneko
et al. 2013).
Materials and methods
A conventional homemade two-electrode electrochemical
bathsetup with labelled diagram shown in Fig. 1(b) was
used in which graphite sheet was used as a counter
electrode and ITO coated glass substrate as a working
electrode. Both electrodes were introduced in the bath
through two steel tubes. The electrolyte solution of 0.25
M concentration was prepared using magnesium nitrate
Mg(NO3)2 salt. Before the deposition process, the
ITO-coated glass substrate was extensively cleaned in an
ultrasonic bath and rinsed with ultrapure water prior to
the deposition in order to remove any surface impurities.
By applying a potential difference of 2.5 V at room tempera-
ture for 30 minutes by HTC power supply DC 3002, a thin
layer of MgO nanostructures was deposited on ITO substrate.
The deposited sample was dehydrated up to 350oC at a
heating rate of 10oC/min in a furnace shown in Fig. 1(c) and
hold for 90 minutes and thencooled at natural/normal atmo-
sphere conditions, finally, MgO nanostructure was formed.
Characterization of the nanostructure
Shimadzu UV-2600 UV-visible Spectrometer was used to
analyze the optical characteristics, and Fourier Transform
Infrared Spectrometer (FTIR) Bruker Alpha was used to
collect data about various functional groups present in the
samplein the range 4000–500 cm-1. The structural and
morphological characterization of the deposited nanostruc-
ture thin films was characterized by X-ray diffraction (XRD,
Model: a Siemens D-5000 X-ray diffractometer) using Cu-Kα
[1.54Å] radiation. The kinetic energy distribution of photo-
electrons released from the specimen material was measured
using X-ray photoemission spectroscopy (Model: Omicron
ESCA (Electron Spectroscope for Chemical Analysis)
Oxford Instrument Germany). In this model aluminium
anode was used for samplesthat have energy 1486.7 eV. SEM
(Model: JSM-7610F Plus & make: JEOL) was used to
analyze the surface morphology and microstructure of depos-
ited MgO nanostructures. The I-V characteristics for hydro-
gensensing were measured by using a Keithley Electrometer
6517A and a pressure-composition-isotherm (PCI) setupat
vacuum (1 *10-3 mbar) and by introducing hydrogen (at 5 bar)
in the stainless-steel chamber.
Results and discussion
Following equations (i-iv) show the overall chemical
reaction for the deposition of MgO nanostructure thin film
using magnesium nitrate salt in aquas medium (Hashaikeh
and Szpunar 2009).
X-ray diffraction (XRD) analysis
Diffraction measurement was carried out with an angular
scanning range of (20° – 80°) to explore the nature of the
material, purity, and crystallinity of the sample. Fig. 2
shows the XRD pattern of synthesized nanostructure thin
films. In Fig. 2, spectrum (a) shows XRD pattern of theuse-
dITO substrate, (b) shows the XRD pattern of thin film
before annealing and (c) shows the XRD pattern of thin
film after annealing. As discussed in equation (iii) and (iv)
the XRD pattern represented by Fig. 2(b) for Mg(OH)2 and
Fig. 2(c) for MgO. The substrate peak marked by (*) is
visible after post annealing at 350°C when conversion of
Mg(OH)2 into MgO nanostructure at ITO substrate (Alsul-
tany et al. 2014).
Fig. 2(c) has distinctive sharp peaks correspond to (111),
(200), (220) and (222) planes related to fcc structure (Cvet-
kovic et al. 2018). The sharp peaks illustrate that the synthe-
sized nanostructure has a good crystalline nature. The
Debye-Scherrer equation (Ashok et al. 2016) was used to
compute the crystallite size D (nm).
where λ, β, and 2θ were the wavelength of the incident
X-ray beam (Cu Kα1.54 Å), full width at half maximum
(FWHM) in radian and Bragg’s diffraction angle of the
preferred orientation. The mean calculated crystalline size
(D) for the deposited nanostructure was determined to be
approximately 36 nm.
A surface-sensitive spectroscopic method (XPS) was used
to determine the various elements present in a material
(also known as its elemental composition), as well as their
chemical state, general electronic structure, and density of
their electronic states. The investigations about surface
composition and chemical state of deposited MgO nano-
structures using core-level light emission were reported
and shown in Fig. 3. It was clear from the survey scan
(Fig. 3a) that the deposited nanostructures were the MgO
nanostructure during the synthesis process and no substan-
tial pollutant was present in the sample. In the survey scan
of the sample, the presence of carbon (C), oxygen (O), and
magnesium (Mg) elements and no major contaminant can be
seen which validate by the elemental signals received.
Contamination of carbon was due to the environmental
presence during the synthesis process which can be seen in
Fig. 3a. The Mg 1s core level at 1302.8 eV is the peak with
the highest intensity in the spectrum of deposited MgO
nanostructure. The peak observed at 531.64 eV corresponds
to O2− in the lattice of MgO.
The core level spectra of Mg2p were also shown in fig. 3d,
where a Gaussian peak of MgO at B.E. 50.91 eV was fitted
using the CASA XPS software, and results indicate that the
nanostructure of MgO was present with Mg lattice, which
also confirms the existence in the core level spectra of Mg 1s
(Fig. 3b) and O 1s (Fig. 3c) where MgO peak also present
with lattice oxygen in the sample. The Mg 2p peak analysis in
Fig. 3d demonstrates that Mg remains in a single chemical
state throughout the development process, and the character-
istic B.E determines its oxidation.
The binding energy of all peaks related to elemental
composition with the electronic state in the survey scan from
Fig. 3(a) is tabulated as follows:
Scanning electron micrograph (SEM) analysis
The SEM micrographs of the deposited MgO nanostruc-
tured thin films were obtained and shown in Fig. 4 together
with the chemical elemental mapping. The inset table
provides information about the elements which were found
in the deposited nanostructure. The results indicate that the
MgO nanostructure was synthesized with porous surface
and deposited accurately by this method. As the number of
porous was more on surface of deposited film than it would
be easy for detecting the gas by increasing the amount of
active area that is available for gas adsorption (Liu et al.
2014; Liu et al. 2016; Musa et al. 2021). The chemical
compositions of the deposited nanostructure thin film on
ITO substrate are also measured by EDX detector which is
inbuilt into SEM. It is also evident that the nanostructure
was adequately present in the form, which supports the
XPS results.
UV-Visible Analysis
The absorption spectra of the synthesized magnesium oxide
nanostructure thin films were obtained in the range of 200
and 800 nm using UV-visible spectrometer. Tauc's formula in
equation (vi) was used to calculate the band gap of synthe-
sized MgO nanostructure (Tauc et al. 1966)
where α, h, ν, C and Eg are the absorption coefficient, Plank’s
constant, frequency of the incident photon, a constant, and
the direct transition band gap respectively. The UV-visible
spectra were shown in Fig. 5, in which Fig. (a) indicates the
absorbance spectrum (b) represents Tauc’s plot to deter-
mine the optical band gap while Fig. (c) denotes the deriva-
tive of absorbance versus energy for verification of band
gap and (d) transmittance spectrum for the deposited MgO
nanostructure. The calculated band gap with the help of the
above equation and extrapolation of the curve as shown in
Fig. 5(b) was found about 4.16 eV, which is less than the
band gap of bulk magnesium oxide (7.8 eV) as reported by
many authors (Bilalbegovic et al. 2004; Guney et al. 2018;
Egwunyenga et al. 2019; Baghezza, 2019). The band gap
was also verified by the derivative versus energy curve
which has a peak at 4.2 eV as shown in Fig. 5(c). The resul-
tant curve was linear throughout a wide range of photon
energy, showing that the deposited nanostructure was a
direct transition material. The band gap of metal oxide
nanostructure decreases due to presence of defect states, so
these defectstates are responsible for the large difference in
band gap energy. Both nanoparticles and nanostructures
exhibit the same trend in band gap energy fluctuation
however, nanostructures have a lower band gap energy
than nanoparticles of the same size because of increased
lattice strain and a larger surface to volume ratio (Abdullah
et al. 2022). Guney and Iskenderoglu, (2018) found that the
band gap of MgO nanostructures varied with thickness
from 4.31 to 4.61 eV and that the band gaps were decreased
as sample thickness increased. The reduction in band gap
may be related to variations in the atomic distance with the
rise in film thickness. Tlili et al. (2021) studied the varia-
tion of band gap from 4.01 to 4.08 eV for different molar
concentrations (0.05, 0.1, 0.15, 0.2 mol·L−1) of Mg2+ ions
by spray pyrolys is technique and reported that, as the
molar concentration of Mg2+ increases, the optical band gap
decreases.
FTIR Analysis
FTIR spectroscopy was used to detect the existence of
organic or inorganic constituents in the deposited nanostructure,
which was connected to various functional groups associated
with specific absorbance peaks in the spectra. The FTIR
spectra of deposited MgO nanostructure thin film with
transmission peaks ranging from 500 to 4000 cm-1 are shown
in Fig. 6. The peak obtained at 545 cm-1 indicates the stretching
vibration of MgO. As a result of the chemicals used during
the synthesis process, the sample also contained additional
functional groups at various peaks corresponding to CO2,
-CO, C-H and -OH, etc.
Electrical properties
The electrical properties such as current-voltage (I–V)
characteristics were measuredin vacuum and with hydrogen
gas by Keithley Electrometer 6517A in the range from -3
volt to 3 voltat room temperature. This study provides
detailed information about the electronic effects in presence
of hydrogen gas on deposited MgO nanostructure thin film.
The curve exhibits considerable nonlinearity compared to a
thin MgO tunnel barrier. It can be seen from Fig. 7 that in
presence of hydrogen gas, the conductivity increases in
forward bias as well as in reverse bias, which can be
explained as the charge shift from hydrogen to the film
structure because hydrogen acts like a donor element. This
property of MgO offers useful information about gas
sensing applications like hydrogen gas and also can be
employed as hydrogen storage materials. A similar study
has been reported for Mg/Ti bilayer thin films (Jangid et al.
2021), Mg-Ni thin films (Jangid and Jangid, 2022) and for
CdTe/Mn bilayer thin films (Nehra et al. 2009) that show
the hydrogen storage properties of these bilayer thin films.
A stainless-steel sealed chamber containing the synthe-
sized sample was usedto measurecurrent-voltage charac-
teristics while exposed to H2 gas in vacuum. The block
diagram and PCI/PCT set up sown in Fig. 8. The resistance
response of synthesized MgO thin film was converted into
a sensitivity value using equation (vii) (Moumen et al.
2019; Musa et al. 2021).
Where R0 stands for the film's resistance in vacuum, and Rg
for its resistance after being exposed to H2 gas. Using
equation (vii), the MgO nanostructure's sensitivity response
to H2 gas was estimated to be about 31%.
Conclusion
The MgO nanostructure thin film was synthesized on
ITO-coated glass substrate at room temperature by a simpli-
fied electrodeposition method using aqueous solution of
magnesium nitrate and investigated by different characteriza-
tion techniques. A cubic structure of MgO with a predicted
crystalline size of about 36 nm was calculated by XRD inves-
tigation. The SEM-EDX image confirms the porous struc-
ture, adherent to the substrate and atomic % of available
elements in the deposited MgO nanostructure thin films. The
elemental composition and chemical states with binding
energy were obtained using XPS. The UV-visible analysis
confirmed the optical band gap of the deposited nanostruc-
ture was ~ 4.16 eV. The I-V characteristics of deposited nano-
structure suggest the partial semiconductor nature and the
conductivity increases in presence of hydrogen. The sensitivity
response of deposited nanostructure was approximately 31%
on exposure to H2 gas. The deposited MgO nanostructures
provide useful information about gas sensing applications
such as hydrogen gas and also can be employed as hydrogen
storage materials. The ultrafine nanostructures (such as QDs
etc.) provide a large and sensitive surface area for a
promising solution to decrease the operating temperature for
metal oxide semiconductor-based gas sensors (Liu et al.
2014; Liu et al. 2016). Their high surface energy allows for
the absorption of gas molecules even at room temperature for
the sensing application.
Acknowledgement
This research work was performed in Dept. of Physics,
University of Rajasthan, Jaipur, India. The author is high
thanks to the Director CNCER, University of Rajasthan,
Jaipur, Rajasthan India for providing characterization
facilities.
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Synthesis of MgO nanostructure thin films via electrodeposition method 58(2) 2023128