Synthesis of MoS2 Thin Film

The two dimensional materials such as graphene, and thin films of transition metal dichalcogenides are became alternative and attracted for use in next generation nanoelectronic devices due to their planar nature and mechanical flexibility. Especially, graphene is promising and most widely studied two-dimensional material for use in flexible and transparent devices. Despite of all these excellent electrical properties, it is difficult to fabricate on/off and logic devices using grapheme because of zero band gap. In contrast, molybdenum disulfide (MoS₂) has the band gap between 1.2 and 1.8 eV as a function of the number of layers (band gap of monolayer MoS₂is 1.8eV) (K. F. Mak, et al., 2010).

Many researchers have been used various methods such as mechanical exfoliation (B. Radisavljevic, et al., 2011), sulfurization (Y. Zhan, et al., 2012), chemical vapor deposition (CVD)(Y. H. Lee, et al., 2012; Y. Shi, et al., 2012) to grow MoS₂ thin film. In the case of mechanical exfoliation, excellent electrical properties were shown. However, there is limitation of mass production. CVD method is a typical method and there are many reports. However, the method for large area MoS₂growth on dielectric substrate at the relatively low temperature is not reported.

In this work, we successfully have grown a few layer MoS₂ thin film (Fig. 1) on a SiO₂ substrate using molybdenum hexacarbonyl (Mo(CO)₆) and hydrogen disulfide (H₂S) by a CVD method. The large area MoS₂ thin film was grown by optimization of the Mo and S precursor ratio and growth conditions such as process pressure and temperature. The properties of the films were analyzed using atomic force microscope (AFM), transmission electron microscope (TEM), and Raman spectroscopy.

References

K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Atomically thin MoS₂: a new direct-gap semiconductor, Phys. Rev. Lett., 105, 136805 (2010).

B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, Single-layer MoS₂ transistors, nature nanotechnology, 6, 147-150 (2011).

Y. Zhan, Z. Liu, S. Najmaei, P. M. Ajayan, and J. Lou, Large-Arae Vapor-Phase Growth and Characterization of MoS₂ Atomic Layers on a SiO₂ substrate, small, 8, 7, 966-971 (2012).

Y. H. Lee, X. Q. Zhang, W. Zhang, M. T. Chang, C. T. Lin, K. D. Chang, Y. C. Yu, J. T. Wang, C. S. Chang, L. J. Li, and T. W. Lin, Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition, Advanced Materials, 24, 17, 2320-2325 (2012).

Y. Ishikawa and K. Kawakami, Structure and Infrared Spectroscopy of Group 6 Transition-Metal Carbonyls in the Gas Phase: DFT Studies on M(CO)_n (M = Cr, Mo, and W; n = 6, 5, 4, and 3), J. Phys. Chem. A, 111, 9940-9944 (2007)

W. K. Hofmann, Thin films of molybdenum and tungsten disulphides by metal organic chemical vapour deposition, J. Mater. Sci., 23, 11, 3981-3986 (1988)