Effects of Reaction Conditions on MoS2 Thin Film Formation Synthesized by Chemical Vapor Deposition using Organic Precur
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Effects of Reaction Conditions on MoS2 Thin Film Formation Synthesized by Chemical Vapor Deposition using Organic Precursor S. Ishihara1, 4, Y. Hibino1, N. Sawamoto1, T. Ohashi2, K. Matsuura2, H. Machida3, M. Ishikawa3, H. Sudo3, H. Wakabayashi2, and A. Ogura1 1 School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan. 2 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan. 3 Gas-phase Growth Ltd, #301 Nokodai-Tamakoganei Venture Port, 2-24-16 Naka, Koganei, Tokyo 184-0012, Japan. 4 Research Fellow of the Japan Society for the Promotion of Science, 5-3-1, Kojimachi, Chiyoda-ku, Tokyo, 102-0083, Japan. ABSTRACT Molybdenum disulfide (MoS2) thin films were fabricated by two-step chemical vapor deposition (CVD) using (t-C4H9)2S2 and the effects of temperature, gas flow rate, and atmosphere on the formation were investigated in order to achieve high-speed low-temperature MoS2 film formation. From the results of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) investigations, it was confirmed that c-axis orientation of the pre-deposited Mo film has a significant involvement in the crystal orientation after the reaction low temperature sulfurization annealing and we successfully obtained 3 nm c-axis oriented MoS2 thin film. From the S/Mo ratios in the films, it was revealed that the sulfurization reaction proceeds faster with increase in the sulfurization temperature and the gas flow rate. Moreover, the sulfurization under the H2 atmosphere promotes decomposition reaction of (t-C4H9)2S2, which were confirmed by XPS and density functional theory (DFT) simulation. INTRODUCTION Two-dimensional molybdenum disulfide (MoS2) has attracted great attention owing to its superior device performances [1]. Various fabrication techniques of MoS2 thin film have been previously introduced, and especially chemical vapor deposition (CVD) can produce high-quality thin film [2]. CVD is mainly classified into two types [3]. The first is regarded as a two-step CVD, in which metal Mo precursor is initially deposited by e-beam evaporation and then sulfurized to form MoS2 [4]. The second is regarded as a one-step CVD, wherein gaseous of Mo and S precursors are simultaneously introduced and react to form MoS2 [5]. Among them, two-step CVD is suitable for the fabrication of large area uniform thin film [6-8]. In general, elemental sulfur powder is mainly used for the sulfurization; however, its low vapor pressure at low temperature region significantly limits the reaction rate. Though hydrogen sulfide is also widely used for two-step CVD, its high toxicity becomes an obstacle. Contrastingly, di-tertiary-butyl disulfide [(t-C4H9)2S2], which is a much safer organic precursor without toxicity and explosibility [9], has a sufficiently high vapor pressure at low temperature. Figure 1(a) shows temperature dependent vapor pressures of elemental sulfur [10], H2S [
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