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▼ [15p-2U-8] Growth of highly-oriented MoS2 thin films over large-area
Keywords:Transition metal dichalcogenides (TMDCs),two-dimensional (2D) material
MoS2 having exceeding potential is recently appeared as a substantial two-dimensional material of graphene. The layered structure of the MoS2 film is illustrated in Fig. 1(a). The MoS2 thin films are generally grown by CVD and exfoliation method. However, general methods have bottleneck in scalability of thin film growth. A main purpose of this study is to explore a growth process of well-ordered MoS2 thin films over large-area. A unique feature of our process is that MoO3-x thin films is used instead of usually used MoO3 powder as a source for sulfurization. Thus, the large-area MoS2 film growth with uniform thickness over entire substrate and high thickness controllability are achievable.
The process is consisted of four steps: MoO3-x thin film deposition, oxidation, sulfurization and post annealing. First, 3nm-thick MoO3-x thin films were thermally evaporated on sapphire substrates in vacuum at a background pressure of 1x10-4 Pa with a rate of 0.1 Å/s. Second, the oxidation process was carried out at 400 °C for 1 hour under the O2 atmosphere to produce crystalline and stoichiometric MoO3 films. The layered structure with the b-axis orientation of the MoO3 was confirmed by X-ray diffraction (XRD) measurement. This process is critical for subsequent MoS2 growth. The third step for the sulfurization was performed with S powder at 500 °C for 15 minutes under the N2 flow gas. X-ray photoelectron spectroscopy clarified that the sulfurized films were composed of MoS2 and MoS3. The fourth step of the post-annealing at 600 °C for 30 minutes under the Ar atmosphere yielded pure MoS2 films. Figure 1(b) shows the XRD pattern of grown MoS2 film. The diffraction peak at 13.9º is assigned to the (002) plane of MoS2, indicating the c-axis orientation. Inset shows an omega scan rocking curve, the full-width at half-maximum of which was 0.116º, demonstrating well-ordered structure. Flat surface morphology with rms of 0.4 nm was observed by atomic force microscopy (Fig.1(c)). The inset shows the MoS2 thin film grown over 15 mm x 15 mm scale. In this manner, our process successfully enabled large scale MoS2 film growth with well-ordered structure and uniform thickness.
The process is consisted of four steps: MoO3-x thin film deposition, oxidation, sulfurization and post annealing. First, 3nm-thick MoO3-x thin films were thermally evaporated on sapphire substrates in vacuum at a background pressure of 1x10-4 Pa with a rate of 0.1 Å/s. Second, the oxidation process was carried out at 400 °C for 1 hour under the O2 atmosphere to produce crystalline and stoichiometric MoO3 films. The layered structure with the b-axis orientation of the MoO3 was confirmed by X-ray diffraction (XRD) measurement. This process is critical for subsequent MoS2 growth. The third step for the sulfurization was performed with S powder at 500 °C for 15 minutes under the N2 flow gas. X-ray photoelectron spectroscopy clarified that the sulfurized films were composed of MoS2 and MoS3. The fourth step of the post-annealing at 600 °C for 30 minutes under the Ar atmosphere yielded pure MoS2 films. Figure 1(b) shows the XRD pattern of grown MoS2 film. The diffraction peak at 13.9º is assigned to the (002) plane of MoS2, indicating the c-axis orientation. Inset shows an omega scan rocking curve, the full-width at half-maximum of which was 0.116º, demonstrating well-ordered structure. Flat surface morphology with rms of 0.4 nm was observed by atomic force microscopy (Fig.1(c)). The inset shows the MoS2 thin film grown over 15 mm x 15 mm scale. In this manner, our process successfully enabled large scale MoS2 film growth with well-ordered structure and uniform thickness.