Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 2, No. 1, 36-37 2018 DOI: 10.33805/2576.8484.111 © 2018 by the author © 2018 by the author History: Received: 13 January 2018; Accepted: 15 January 2018; Published: 19 January 2018 Layer-by-Layer Thinning of 2D Materials Viet Phuong Pham SKKU Advanced Institute of Nano Technology (SAINT), Sungkyunkwan University (SKKU), Suwon, Republic of Korea; pvphuong85@ibs.re.kr (V.P.P.). 1. Introduction Two-dimensional (2D) structured materials are receiving huge interests since the discovery of graphene material first by the mechanical exfoliation method using scotch tape from the graphite in 2004 (1). Among them, graphene [1-15] molybdenum disulfide (MoS2) [10,16] black phosphorous [17] hexagonal-boron nitride (h-BN) [18-20] hafnium dioxide (HfO2) [21] molybdenum diselenide (MoSe2) [22] and 2D carbide nanosheets (MXene) [23] are emerging as many promising potential materials with novel properties in electronics and optoelectronics. Unlike conductive graphene with gapless characteristics, other materials above present different energy band - gap. The controlled tuning of band-gap of 2D materials by layer-by-layer thinning using various strategies related to chemistry, physic, nanotechnology, and engineering in order to obtain the ultra-thinner material layer and resulting in improvement their electrical characteristics is highly desiring with targeting toward practical applications in the industry to serve human society (Figure 1). Figure 1. Schematic of strategies for layer-by-layer thinning on various low-dimensional material surfaces by chemistry, physic, nanotechnology and engineering for tuning their electronics and optoelectronics. The increasing the controlled band-gap of 2D materials would be raising up the current on-off ratio, photoluminescence, and other unexploited and unexplored exotic properties. The electronic properties of 2D layered materials are strongly dependent on their thicknesses. For instance, the thickness modulating of MoS2 layers will activate the optical energy gap which makes it promising for application in optoelectronic devices, such as photodetectors, photovoltaics, light emitters, phototransistors. Very recently, the progress in layer-by-layer thinning techniques on 2D materials has significant achieved [15-17,19-23]. By adjusting the etching rates (chemical and physical plasma engineering) [15-17,19-22] or gas molecular ratios and temperatures (chemical vapor deposition system) [23] we can achieve complete removal the mailto:pvphuong85@ibs.re.kr 37 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 2, No. 1: 36-37, 2018 DOI: 10.33805/2576.8484.111 © 2018 by the author layer-by-layer precisely and controllability [15-17,19-23]. Especially, the layer-by-layer etching by plasma (inductively coupled plasma, ion beam) without inducing the physical and chemical damage has successfully demonstrated in recent reports [15,17]. Consequently, it could unlock and take a leap forward on developing plasma-based thinning methods for other TMDs and low-dimensional materials in various advanced devices and applications. References [1] K. S. Novoselov et al., "Electric field effect in atomically thin carbon films," Science, vol. 306, no. 5696, pp. 666-669, 2004. https://doi.org/10.1126/science.1102896 [2] V. P. Pham, H.-S. Jang, D. Whang, and J.-Y. Choi, "Direct growth of graphene on rigid and flexible substrates: Progress, applications, and challenges," Chemical Society Reviews, vol. 46, no. 20, pp. 6276-6300, 2017. https://doi.org/10.1039/c7cs00224f [3] V. P. Pham et al., "Chlorine-trapped CVD bilayer graphene for resistive pressure sensor with high detection limit and high sensitivity," 2D Materials, vol. 4, no. 2, p. 025049, 2017. https://doi.org/10.1088/2053-1583/aa6390 [4] V. P. Pham, K. N. Kim, M. H. Jeon, K. S. Kim, and G. Y. Yeom, "Cyclic chlorine trap-doping for transparent, conductive, therm ally stable and damage-free graphene," Nanoscale, vol. 6, no. 24, pp. 15301-15308, 2014. https://doi.org/10.1039/c4nr04387a [5] V. P. Pham, K. H. Kim, M. H. Jeon, S. H. Lee, K. N. Kim, and G. Y. Yeom, "Low damage pre-doping on CVD graphene/Cu using a chlorine inductively coupled plasma," Carbon, vol. 95, pp. 664-671, 2015. https://doi.org/10.1016/j.carbon.2015.08.070 [6] V. P. Pham, A. Mishra, and G. Y. Yeom, "The enhancement of hall mobility and conductivity of CVD graphene through rad ica l doping and vacuum annealing," RSC Advances, vol. 7, no. 26, pp. 16104-16108, 2017. https://doi.org/10.1039/c7ra01330b [7] V. P. Pham et al., "Low energy BCl3 plasma doping of few-layer graphene," Science of Advanced Materials, vol. 8, no. 4, pp. 8 8 4 -8 90 , 2016. [8] V. Pham, "Chemical vapor deposited graphene synthesis with same-oriented hexagonal domains," Eng Press, vol. 1, pp. 39-42, 2018. [9] K. N. Kim, V. P. Pham, and G. Y. Yeom, "Chlorine radical doping of a few layer graphene with low damage," ECS Journal o f So l id State Science and Technology, vol. 4, no. 6, pp. N5095-N5097, 2015. https://doi.org/10.1149/2.0141506jss [10] V. P. Pham and G. Y. Yeom, "Recent advances in doping of molybdenum disulfide: Industrial applications and future p rosp ects," Advanced Materials, vol. 28, no. 41, pp. 9024-9059, 2016. https://doi.org/10.1002/chin.201651225 [11] A. Ferrari, F. Bonaccorso, and V. Fal'ko, "Science and technology roadmap for graphene, related two-dimensional c ry sta ls, and hybrid systems," Nanoscale, vol. 7, pp. 4587-5062, 2015. [12] S. Z. Butler et al., "Progress, challenges, and opportunities in two-dimensional materials beyond graphene," ACS Nano, vol. 7, no. 4 , pp. 2898-2926, 2013. [13] A. K. Geim and K. S. Novoselov, "The rise of graphene," Nature Materials, vol. 6, no. 3, pp. 183-191, 2007. [14] W. J. Parak, A. E. Nel, and P. S. Weiss, "Grand challenges for nanoscience and nanotechnology," vol. 9, ed: ACS Publications, 2015, pp. 6637-6640. [15] K. Kim et al., "Atomic layer etching of graphene through controlled ion beam for graphene-based electronics," Scientific Reports, v ol. 7, no. 1, pp. 2462-2462, 2017. https://doi.org/10.1038/s41598-017-02430-8 [16] Y. Liu et al., "Layer-by-layer thinning of MoS2 by plasma," ACS Nano, vol. 7, no. 5, pp. 4202-4209, 2013. [17] J. Park, S. Jang, D. Kang, D. Kim, and M. Jeon, "Layer-controlled thinning of black phosphorous by an ar ion beam," Journal Mater Chem, vol. 5, pp. 10888-10893, 2017. https://doi.org/10.1039/c7tc03101g [18] C. R. Dean et al., "Boron nitride substrates for high-quality graphene electronics," Nature Nanotechnology, vol. 5, no. 10, pp. 722-726, 2010. [19] C. Elbadawi et al., "Electron beam directed etching of hexagonal boron nitride," Nanoscale, vol. 8, no. 36, pp. 1 6 1 82 -1 618 6, 2 0 16. https://doi.org/10.1039/c6nr04959a [20] Y. Liao et al., "Oxidative etching of hexagonal boron nitride toward nanosheets with defined edges and holes," Scientific Reports, vol. 5, no. 1, p. 14510, 2015. https://doi.org/10.1038/srep14510 [21] J. Chen, W. J. Yoo, Z. Y. Tan, Y. Wang, and D. S. Chan, "Investigation of etching properties of HfO based high-K dielectrics u sing inductively coupled plasma," Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 22, no. 4 , p p . 1 5 5 2 -15 58, 2004. https://doi.org/10.1116/1.1705590 [22] Y. Sha, S. Xiao, X. Zhang, F. Qin, and X. Gu, "Layer-by-layer thinning of MoSe2 by soft and reactive p lasma e tch ing," Applied Surface Science, vol. 411, pp. 182-188, 2017. https://doi.org/10.1016/j.apsusc.2017.03.159 [23] B. Ding et al., "A two-step etching route to ultrathin carbon nanosheets for high performance electrical double lay er c ap ac itors," Nanoscale, vol. 8, no. 21, pp. 11136-11142, 2016. https://doi.org/10.1039/c6nr02155g https://doi.org/10.1126/science.1102896 https://doi.org/10.1039/c7cs00224f https://doi.org/10.1088/2053-1583/aa6390 https://doi.org/10.1039/c4nr04387a https://doi.org/10.1016/j.carbon.2015.08.070 https://doi.org/10.1039/c7ra01330b https://doi.org/10.1149/2.0141506jss https://doi.org/10.1002/chin.201651225 https://doi.org/10.1038/s41598-017-02430-8 https://doi.org/10.1039/c7tc03101g https://doi.org/10.1039/c6nr04959a https://doi.org/10.1038/srep14510 https://doi.org/10.1116/1.1705590 https://doi.org/10.1016/j.apsusc.2017.03.159 https://doi.org/10.1039/c6nr02155g