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Monolayer molybdenum disulfide (MoS2) has recently aroused the great interest of researchers due to its direct-gap property and potential applications in electronics, catalysis, photovoltaics, and optoelectronics. Chemical vapor deposition (CVD) has been one of the most practical methods of synthesizing large-area and high-quality monolayer MoS2. However, The process of preparation is complex and cumbersome. Here we report that high-quality monolayer MoS2 can be obtained through using sulfurization of MoO3 by a simple and convenient CVD on sapphire substrates.The substrate cleaning is simplified. Substrates are cleaned in detergent solution, deionized water and acetone without sopropanol or piranha solution (H2SO4/H2O2=3:1) in sequence, avoiding their potential dangers. The MoO3 powder (Alfa Aesar, 99.995%, 0.02 g) is placed in an alumina boat, and a sapphire substrate is faced down and is placed 6 cm away from MoO3 powder in the same boat. The sapphire substrate is placed in the center of the heating zone of the furnace. Another alumina boat containing sulfur powder (Alfa Aesar, 99.999%, 0.2 g) is placed upstream with respect to the gas flow direction in the low temperature area. We adopt an atmospheric pressure chemical vapor deposition method, so it does not require a vacuum process. After 30 min of Ar purging, the furnace temperature is directly increased from room temperature to 800 ℃ in 30 min, reducing the heating steps. After 60 min, the furnace is cooled down naturally to room temperature. Optical microscopy (OM) images, Raman spectra and photoluminescence (PL) are all obtained by confocal Raman microscopic system (LabRAM HR Evolution). From the OM images, we can see that isolated islands (triangles) have edge lengths up to 50 m, which is far larger than that grown by micromechanical exfoliation. The color of the triangles is uniform, which has a strong contrast with the substrate. We can obtain a preliminary result that the sample is a uniform monolayer MoS2. Raman spectra are collected for MoS2 samples on sapphire substrates. Two typical Raman active modes can be found: E2g1 at 386.4 cm-1 and A1g at 406 cm-1 ( =19.6 cm-1), which correspond to single-layered MoS2 sample. Raman mapping shows that the sample is a uniform monolayer MoS2. The PL spectrum of MoS2 shows a pronounced emission peak at 669 nm, which is consistent with other reported results for MoS2 thin sheets obtained from exfoliation methods. When the layer number of MoS2 decreases, with its bandgap transforming from indirect to direct one, the fluorescence efficiency will be significantly enhanced. So the results further prove that the sample is high-quality monolayer MoS2.
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Keywords:
- monolayer MoS2 /
- chemical vapor deposition /
- Raman spectroscopy /
- photoluminescence spectroscopy
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[16] Jeon J, Jang S K, Jeon S M, Yoo G, Jang Y H, Park J H, Lee S 2012 Nanoscale 00 1
[17] Lee C, Yan H, Brus L E, Heinz T F, Hone J, Ryu S 2010 ACS Nano. 4 2695
[18] Splendiani A, Sun L, Zhang Y, Li T, Kim J, Chim C Y, Galli G, Wang F 2010 Nano Lett. 10 1271
[19] Mak K F, He K, Shan J, Heinz T F 2012 Nat. Nanotechnol. 7 494
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[1] Coehoorn R, Haas C, Dijkstra J, Flipse C J F 1987 Phys. Rev. B 35 6195
[2] Wang Q H, Kalantar-Zadeh K, Kis A, Coleman J N, Strano M S 2012 Nat. Nanotechnol. 7 699
[3] Radisavljevic B, Radenovic A, Brivio J, Giacometti V, Kis A 2011 Nat. Nanotechnol. 6 147
[4] Mak K F, Lee C G, Hone J, Shan J, Heinz T F 2010 Phys. Rev. Lett. 105 13
[5] Zha L Y, Fang L, Peng X Y 2015 Acta Phys. Sin. 64 018710 (in Chinese) [张理勇, 方粮, 彭向阳 2015 64 018710]
[6] Xu D D, Wang X B, Qiu J L, Zhao Z F 2015 Chin. J. Colloid Polym. 33 37 (in Chinese) [徐豆豆, 王贤保, 邱家乐, 赵真凤 2015 胶体与聚合物 33 37]
[7] Gu P C, Zhang K L, Feng Y L, Wang F, Miao Y P, Han Y M, Zhang H X 2016 Acta Phys. Sin. 65 018102 (in Chinese) [顾品超, 张楷亮, 冯玉林, 王芳, 苗银萍, 韩叶梅, 张韩霞 2016 65 018102]
[8] Perkgoz N K, Bay M 2016 Nano-Micro Lett. 8 70
[9] Novoselov K S, Jiang D, Schedin F 2005 Proc. Natl. Acad. Sci. U.S.A 102 10451
[10] Zeng Z Y, Yin Z Y, Huang X, Li H, He Q Y, Lu G, Boey F, Zhang H 2011 Angew Chem. Int. Ed. 50 11093
[11] Yan Y, Xia B, Ge X, Liu Z, Wang J Y, Wang X 2013 ACS Appl. Mater. Interfaces 5 12794
[12] Lee Y H, Zhang X Q, Zhang W J, Chang M T, Lin C T, Chang K D, Yu Y C, Tse J, Wang W, Chang C S, Li L J, Lin T W 2012 Adv. Mater. 24 2320
[13] Zhan Y J, Liu Z, Najmaei S, Ajayan P M, Lou J 2012 Small 8 966
[14] Lin Y C, Zhang W J, Huang J K, Liu K K, Lee Y H, Liang C T, Chu C W, Li L J 2013 Nano Lett. 13 1852
[15] van der Zande A M, Huang P Y, Chenet D A, Berkelbach T C, You Y M, Lee G H, Heinz T F, Reichman D R, Muller D A, Hone J C 2013 Nat. Mater. 12 554
[16] Jeon J, Jang S K, Jeon S M, Yoo G, Jang Y H, Park J H, Lee S 2012 Nanoscale 00 1
[17] Lee C, Yan H, Brus L E, Heinz T F, Hone J, Ryu S 2010 ACS Nano. 4 2695
[18] Splendiani A, Sun L, Zhang Y, Li T, Kim J, Chim C Y, Galli G, Wang F 2010 Nano Lett. 10 1271
[19] Mak K F, He K, Shan J, Heinz T F 2012 Nat. Nanotechnol. 7 494
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