Effects of post-annealing on MoS2 thin films synthesized by multi-step chemical vapor deposition

Multi-step chemical vapor deposition (CVD) is a synthesis method which is capable of producing a uniform, large area, and high-quality thin films. In this work, we report the effect of post-annealing on the structural and optical properties of few-layers (FL) MoS2 thin films synthesized by multi-step CVD. Based on atomic force microscopic image, the thickness of the MoS2 thin film is similar to 3 nm, which is equivalent to five layers. After annealing at 900 degrees C for 17 min, intensity of the A(1g) and E-2g(1) full-width-at-alf-maximum (FWHM) Raman modes increased by similar to 3 times while the reduced from similar to 10 cm(-1) to similar to 7.5 cm(-1) for A(1g) and from similar to 13.6 cm(-1) to similar to 7.5 cm(-1) for E-2g(1). Both of the as-grown and annealed samples showed X-ray (002) diffraction peak at 14.2 degrees but the intensity was more prominent for the annealed sample. It was found that the annealed sample showed clear and distinct absorbance peaks at 666, 615, 448, 401, and 278 nm which correspond to the A, B, C, D, and E excitons, respectively. The results indicate that annealing significantly improved the optical and structural quality of the MoS2 film. Field-effect transistor based on annealed MoS2 thin film was fabricated and showed electron mobility of 0.21 cm(2)V(-1)s(-1), on/off ratio of 1.3 x 10(2) and a threshold voltage of 0.72 V. Our work highlights the importance of high-temperature annealing in multi-step CVD to obtain a uniform and high-quality FL MoS2 thin films.

Automated summary

Multi-step chemical vapor deposition (CVD) is capable of producing high-quality thin films, and this study focuses on the effects of post-annealing on the structural and optical properties of MoS2 thin films. The results demonstrate that annealing significantly improves both the optical and structural quality of the MoS2 film.