229 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 Optical Properties of SnS2 Thin films Prepared By Chemical Spray Pyrolysis N. A. Hussain Department of Physics , College of Science, University of Al-Mustansiriya Received in: 18 January 2012, Accepted in: 21 May 2012 Abstract Thin films of tin disulphide SnS2 with different thicknesses (2500,4000,5000)A0 have been prepared by chemical spray pyrolises technique on substrate of glass with temperature (603)K . The effect of thickness on the optical properties of SnS2 has been studied.the optical study that includes the absorptance and transmittance spectra in the wavelength range (300- 900)nm demonstrated that the value of absorption coefficient (α) ) was greater than (104 cm-1) the electronic transitions at the fundamental absorption edge were of the indirect kind whether allowed and forbidden . Absorption edge shift slightly towards higher wave length.The value of energy gaps (Eg) for all the films prepared are decreased with increasing the thickness. Absorption and transmission spectra were used to find the optical constant including refractive index(n), extinction coefficient (k), imagenary and real part of dielectric constant (£i , £r), and it was found that all the optical constant was affected . Key word: tin disulphide, SnS2 Optical properties , thin films Introduction Tin forms a variety of sulfides, SnS2, Sn2S3, Sn3S4, Sn4S5, SnS and numerous polysulfide anions . Due to their electrical and optical properties these binary compounds have a high potential use in opto-electronic devices and photocondu- ctive cells . Tin disulfide was first synthesized some 200 years ago and has more than 70 polytype structures . Tin disulfide adopts the PbI2 layered structure with hexagonal unit cell, in which tin atoms are located in the octahedral sites betwen two hexagonally close packed sulfur slabs to form sandwich structure.The SnS2 SnS2 layer is stacked on top of one other along the crystallographic c-axis and is held together by weak Van der Waals forces . Present day technologists are busy using these materials in designing opto-electronic devices, a part of solar collectors, etc. Thin films of tin sulfides have been grown by spray pyrolysis , chemical bath , and chemical vapour deposition either from organometallic precursors [1,2,3,4]. High absorption region observed for most semiconductors at α ≥ 104 cm-1 , the absorption is due to the transitions between extended states in both bands.The imperial formula that governs this transition have been found by Tauc[5] And Kaliannan Optical properties of SnS2 thin films were studied by Thangaraju found that the SnS 2 thin films which prepared by chemical spray pyrolysis had a high absorption cofficoent and allowed dirct transition were observed in films[11]. Optical properties of SnS2 thin films were studied by C. Cifuentes ,et.al.[12] they ound SnS2 thin films had a high absorption coefficient (greater than 104 cm-1) and an energy band gap Eg of about 1.3 eV, indicating that this compound has good properties to perform as absorbent layer in thin film solar cells. 230 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 The aim of this research is a preparation of SnS2 thin films and studying the optical properties The main task was the effect of the thickness on optical properties of SnS2 thin films which were prepared by using the chemical spray pyrolysis technique. Experimental :- SnS2 thin films were prepared by spray pyrolysis of aqueous solution of( SnCl4.H2O) and thiourea NH2SCNH2 . The molar concentration of the solution equals to 0.3 mole/liter.In order to prepare the solution 0.1 molar few grams[( 2.62935 gm )SnCI4 .H2O , and ( 0.57093 gm ) NH2SCNH2 concentrations from these two materials are weighted by electronic balance (Mettler AE-160) with sensitivity( 10-4 gm) needed from each of them , melated in 25 cm3 of distilled water , according to the following equation: M = ( Wt / Mwt ) . ( 1000/ V )……….(1) Wt: weight of the material (gm) V: Volum of water (ml) M:molarity(mol/l) Mwt: Molecular weight (gm/mol) This composition was optimum to give higher optical transparency . The obtained solution is immediately sprayed by used double nozzle sprayer on to heated.Substrate of glass plates, the upper container of the nozzle has 4 cm diameter and was connected to capillary of 0.127 mm through the stopcock .The capiliary was surrounded by a tube through which the compressed air was blown at 2Kg cm-2 . The sprayer set up has been described. The substrate were heated to a temperature of about 603 K for 20 min before spraying in small amounts to avoid excessive cooling of hot substrate during spraying .The distance between sprayer and substrate was kept 30 cm and spray rate was 10 cm3 min-1 . The period of sprying sec thin stopping period for 55 sec reproducible films were obtained from successive runs.the chemical reaction can be described in equation as: NH2SCNH2 + 4H2O → 2H2S + 4NH3 +↑ 2CO2….(2) SnCI6 + 2H2S + 4H2O → SnS2 +4 H3O- + 6CI- ……….(3) The transmission and absorption spectra were obtained over the range (300-900)nm by using UV-VISIBALE recording spectrometer (Shimadzu model UV-160). The absorption coefficient (α), refractive index(n) and extinction coefficient (k)has been calculated from the equations respectively [5]: α = 2.303A/t………………….(4) [(R+1)/(R-1)]-K2)1/2-n= …(5) k= αλ/4π…………………………(6) Where R is the reflectance , t is the thickness of the sample which measured by Gravimetric method ,the real and imaginary part of dielectric constant (εr)and (εi)can be calculated by using equation: [9,10] 231 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 εr= n2 – k2……………(7) ε i = 2nk……………………….(8) Results and Discussion Fig( 1,2) shows the absorptance and reflectance spectrum for SnS2 thin films as a function of thickness t =(2500,4000,5000 )A0 from these spectrum the energy gap and optical constants have been determined in general, the absorption edge shifting to higher wavelength.Also the absorptance increase with the increase of thickness and the reflectivity is increased in range(1.3-2.35) eV then the reflectivity is decrease till to highest value. The dominate feature of energy (hυ) dependence of the absorption (α) is the onset of absorption near the region of interband transitions from valance band to conduction band at α > 104 cm- 1 the optical energy gap of materials E+g obtained from the equation(9) near the band edge[11,12]: αhѵ=B(hѵ-Eg)r ..(9) Where B is constant , r is a number = 2 for allowed direct transition , and r= 3 for forbidden direct transition.Fig (3 ) shows the variation of the absorption coefficient with photon energy which calculated from equation (3) as a function of thickness, it is found in 700 nm that α increased with the increase of thickness from (0.357-0.365-0.432)x104 )cm-1 for ( t=2500,4000 and5000 )A0respectively and this attributed to the increase of concentration by the increase of thickness led to increase in the number of collisions with material and an increase in the values of absorption coefficient ( α).[10] The variation of (αhυ)1/2 and (αhυ)1/3 as a function of hυ are shown in Figs (4,5 ) for indirect transitions for three value of thickness. The band gap energy is obtained by intercepting the linear portion of the absorption curves to the energy axis [11 ]. The values of optical energy gap as shown in table (1) from this result the value of Eg decreased for all transitions with the increase of thickness .[6] Fig(6) shows the variation of K with wavelength, we can see from this figure that the value of K increases with the increase of thickness due to the increase of the number of photon collisions with the material this increase resulted to increasing value of absorption coefficient and this agrees with equation(6).the refractive index (n)which calculated from equation(5) is shown in Fig ( 7) and its increase with thickness this agree with the result in reference[12]. Also Figs (8,9 ) show the variation of the imaginary and real part of dielectric constant (εiand εr ) as a function of thickness and photon energy which were calculated from the equation (7 ,8 ) . The behavior of εr is similar to( n) due to the smaller value of K2 comparison of n2 in equation( 7 )so high value of the curves with the increase of thickness, while εi is mainly depends on the K values, which are related to the variation of α, its found that εi increases with the increase of thickness. Conclusions 1The absorptance increases with the increase of thickness and the absorption edge shifting to higher wave length,the reflectivity is increased in the range (300-550)nm then decreased. 2- Its found that α,the value of extinction coefficient and refractive index (n) increases with the increase of thickness. 3- It is found that εi, εr increases with the increase of thicknesses. 232 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 4- The value of Eg decreased for all transitions with the increase of thicknesses. Reference 1- Jaing . T and Ozin G.A . ( 1998 ), New Directions in Tin Sulfide Materials Chemistry , J. Mater. Chem. 8 , 1099. 2-Patil S .G and Fredgold. R.H, ( 1971) " Synthesis of SnS2 nanoparticles by a surfactant- mediated hydrothermal method and their characterization", " J. Pure Appl. Phys ". 4 ,718. 3- Woulfe ,P, Philos and Trans. R. Soc. (1971) London 61 , 114. 4- Engleken , R.D, Mccloud ,H.D, Lee ,C. Slayton .M and Ghoreishi .H, (1987) ,Low temperature chemical precipitation and vapor deposition of thin films ," J. Electrochem. Soc ", 134 , 2696 . 5- Ravichandran, D.; Francis Xavier, P.; Sasikala, S. and Moorthy Babu, (1996), Photoconductivity studies of CdSe1−xTex thin films as a function of doping concentratio, Bull. Master Sci, 19, 3,437. 6-Thangaraju, B . and Kaliannan, P .(2000), Spray pyrolytic deposition and characterization of SnS and SnS2 thin films , J.phys D:Appl . phys, 33:1054-1059. 7-Cifuentes,C.;Botero,M.;Romero,E.;Calderón,C. and Gordillo ,G.(2006), Optical and structural studies on SnS films grown by co-evaporation,Braz.J..36, (3b) J.phys 8- Yang, Q.;Tang,K.;Wang,C.;Zuo, j.;Zhang, D. and Qian, Y.(2003), Preparation of SnS2 colloidal ε quantum dots and their application in organic/inorganic hybrid solar cells , thin solid films , 436, P.203-207. 9- Budyonnaya, L.; Shinkman, M.; Sanitarov, V. and Kalinkin (1983), 'Sov.phys. Semiconductor,17, P. 611. 10-Hala,A. Saheeb , MSc thesis, AL-Mustansirya University, (2006), Study influence for thickness and annealing on optical properties for CuO thin films prepared by chemical spray pyrolysis. 11- Ji, Y.;Zhang, H.;Ma, X, XuJ and Yang, D. (2003), Preparation of SnS2 thin films by chemical bath deposition" " J.Phys, Condens.Mater, 15, P. 661-665. 12- Madan,A. and Shaw, M. (The physics and applications of amorphous semiconductors, cademic press, ed-Madan, In . New York 1986.cademic press, ed-Madan, In . New York 1986. Table( 1): shows the variation of optical energy gap of SnS2 thin films with thickness. Eg(eV)at r=3 Eg(eV)at r=2 Thickness(A0) 0.2 1.3 2500 0.15 1.24 4000 0.1 1.2 5000 http://www.google.iq/url?sa=t&rct=j&q=Engleken+R.D%2C+Mccloud+.H.D%2C+Lee+.C%2C+Slayton+.M%2C+Ghoreishi+.H%2C+%281987%29%27+J.+Electrochem.+Soc+%22.+134+%2C+2696+.&source=web&cd=1&ved=0CCQQFjAA&url=http%3A%2F%2Fcat.inist.fr%2F%3FaModele%3DafficheN%26cpsidt%3D7646100&ei=P8STT9etN6nN4QTTpMjQDw&usg=AFQjCNEupGOJe-HeE-KJ3iwbBaHno8crYQ&cad=rja http://www.google.iq/url?sa=t&rct=j&q=Engleken+R.D%2C+Mccloud+.H.D%2C+Lee+.C%2C+Slayton+.M%2C+Ghoreishi+.H%2C+%281987%29%27+J.+Electrochem.+Soc+%22.+134+%2C+2696+.&source=web&cd=1&ved=0CCQQFjAA&url=http%3A%2F%2Fcat.inist.fr%2F%3FaModele%3DafficheN%26cpsidt%3D7646100&ei=P8STT9etN6nN4QTTpMjQDw&usg=AFQjCNEupGOJe-HeE-KJ3iwbBaHno8crYQ&cad=rja http://www.springerlink.com/content/f01479x817586n81/ 233 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 100 200 300 400 500 600 700 800 900 1000 Wave Length ( ) (nm ) 0.0 0.2 0.4 0.6 0.8 1.0 A bs or pt io n ( A ) t=2500 A t=4000 A t=5000 A SnS Fig.(1): The absorption spectrum of SnS2 thin films With different thickness 200 400 600 800 1000 Wave length ( ) (nm) 0.0 0.1 0.2 0.3 Re fle ct an ce (R ) t=2500A t=4000A t=5000A SnS2 Fig .(2):The reflectance spectrum of SnS 2 thin films with different thicknesses Fig.(3): The variation absorption coefficient of SnS2 thin films with photon energy as a function of thickness 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Photon Energy ( eV ) 0 1 2 3 A bs or pt io n C of fic ie nt ( ) cm x 10 -1 t=2500A t=4000A t=5000A SnS2 4 234 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 1 2 3 4 Photon Energy(eV) 50 100 150 200 250 300 ( hv ) ( cm .e V) -1 1/ 2 1/ 2 SnS2 t=5000A t=4000A t=2700A Fig(4):shows plots (αhv)1/2 against photon energy of SnS2 thin films prepared at different thicknesses 1 2 3 4 Photon Energy(eV) 10 20 30 40 50 ( hv )(c m .e V) -1 1/ 3 1/ 3 SnS2 t=5000A t=4000A t=2500A Fig(5):shows plots (αhv)1/3 against photon energy of SnS2 thin films prepared at different thicknesses 235 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Photon Energy ( eV ) 0.0 0.2 0.4 0.6 0.8 Ex tin ct io n C of fic ie nt ( K ) t=2500A t=4000A t=5000A SnS2 Fig(6):The variation of extinction coefficient with photon energy for SnS2 thin filmsas a function of thickness Fig(7):The variation of the refractive index with photon energy for SnS2 thin films as a function of thickness 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Photon Energy ( eV ) 1.0 1.2 1.4 1.6 1.8 2.0 R ef re ct iv e In de x ( n ) t=2500A t=4000A t=5000A 236 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Photon Energy ( eV ) 0.0 0.5 1.0 1.5 2.0 2.5 Im ag en ar y Pa rt o f D ie le ct ri c C on st an t ( i ) t=2500A t=4000A t=5000A SnS2 Fig(8):The variation of the imaginary part of the dielectric constant with photon energy for SnS2 thin films as a function of thickness 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Photon Energy ( eV ) 1.0 1.5 2.0 2.5 R ea l P ar t o f D ie le ct ri c C on st an t ( r) t=2500A t=4000A t=5000A SnS2 Fig(9):The variation of the real part of the dielectricconstant with photon energy for SnS2 thin films as a function of thickness 237 مجلة إبن الهيثم للعلوم الصرفة و التطبيقية 2012 السنة 25 المجلد 2 العدد Ibn Al-Haitham Journal for Pure and Applied S cience No. 2 Vol. 25 Year 2012 المحضرة بطريقة الرش الكيميائي الحراري SnS2الخواص البصرية ألغشية نضال علي حسين الجامعة المستنصرية ¡كلية العلوم ¡قسم الفيزياء 2012ايار 21البحث في : قبل 2012كانون الثاني 8استلم البحث في: الخالصة Chemical spray))بطريقـة الـرش الكيميــائي الحـراري SnS2حضـرت اغشـية رقيقــة مـن ثنــائي كبريتيـد القصــدير ( pyrolysis technique) 603علـى قواعـد مـن الزجــاج مسـخنة بدرجـة حـرارة)K وبســمك (A)2500,4000,5000(. ÓÑÏ ) nm äÇ(900-300الخـواص البصـرية التـي تضـمنت اطيـاف االمتصاصـية والنفاذيـة فـي المـدى الطيفـي تاثير السمك في ) كمـــا وجـــد ان االنتقـــاالت االلكترونيـــة عنـــد حافـــة 104cm-1) لالغشـــية المختلفـــة اكبـــر مــن ( αقــيم معامـــل االمتصـــاص ( ح والممنـوع وان قيمــة فجــوة الطاقـة البصــرية فــي االمتصـاص االساســية كانـت مــن نــوع االنتقـال غيــر المباشــر بنوعيـه المســمو حالـة االنتقــال غيــر المباشــر المســموح تقــل بازديــاد الســمك كمـا اســتعملت اطيــاف االمتصاصــية والنفاذيــة فــي ايجــاد الثوابــت .البصرية المتضمنة الجزء الحقيقي والخيالي لثابت العزل ومعامل الخمود ومعامل االنكسار الخواص البصرية ,االغشية الرقيقة ,ثنائي كبريتيد القصدير: ةمفتاحيالكلمات ال 4- Engleken , R.D, Mccloud ,H.D, Lee ,C. Slayton .M and Ghoreishi .H, (1987) ,Low temperature chemical precipitation and vapor deposition of thin films 6-Thangaraju, B . and Kaliannan, P .(2000), Spray pyrolytic deposition and characterization of SnS and SnS2 thin films , J.phys D:Appl . phys, 33:1054-1059.