Thin film molybdenum disulfide (MoS₂) exhibits unique physical and electrochemical properties. Most notably MoS₂ has shown itself to be a viable candidate as an earth abundant catalyst for the hydrogen evolution reaction (HER) [1-3]. However, preparation of quality MoS₂ thin films often involves complex synthesis techniques not capable of large-scale production. In this paper we present a study of thin film MoS₂ prepared by radio frequency (RF) magnetron sputtering, which is an industrial large-scale thin film fabrication method. Substrate temperature during deposition and its effect on the morphology, electrical – and optical properties of the sputtered MoS₂ thin films will be investigated.

The MoS2 thin films were deposited at room temperature (RT) and 400°C using an Argon atmosphere with a pressure of 5.9 mTorr, and RF power of 150W. Following deposition the samples were annealed at 550°C for three hours. A visual representation of the thin film MoS₂ on quartz substrate after the annealing process is seen in Figure 1. Visually the MoS₂ films have a gold brown color, where the sample deposited at room temperature is slightly darker. The absorbance spectra (250-850 nm) show that the film deposited at room temperature display no peaks associated with MoS₂, while the thin film deposited at 400°C show a small 'C' transition peak at ~418 nm (Figure 2). Post annealing absorbance spectra of both films indicate the four transition peaks characteristic of MoS₂. The 'A' and 'B' peaks are direct transitions related to the band-edge excitons, whereas the 'C' and 'D' absorbance peaks arise from van Hove singularities in the electronic density of states associated with layered MoS₂ [4,5]. X-ray diffraction (XRD) was performed using a Si substrate and the existence of the (002) plane indicates that the thin films are crystalline (Figure 3).

In conclusion, we have determined the effect of substrate temperature during deposition and post annealing on the properties of the MoS₂ thin films. Additionally, preparation of crystalline MoS₂ has been demonstrated using a large-scale thin film production technique. The morphology, optical – and electrical properties have been studied on ITO glass and quartz substrates.

References

1. Wang, D.; Zhang, X.; Bao, S.; Zhang, Z.; Fei, H. & Wu, Z. J. Mater. Chem. A, The Royal Society of Chemistry, 2017, 5, 2681-2688
2. Hong Li, C. T., Ai Leen Koh, Lili Cai, Alex W. Contryman, Alex H. Fragapane, Jiheng Zhao, Hyun Soo Han, Hari C. Manoharan, Frank Abild-Pedersen, Jenk K. Nørskov, and Xiaolin Zheng (2016). Nature Materials 15
3. Haotian Wang, C. T., Desheng Kong, Karen Chan, Frank Nano Reasearch 8: 566-575.
4. Mak, C. Lee, J. Hone, J. Shan, and T. Heinz, Phys. Rev. Lett. 105, 136805 (2010).
5. Britnell et al., Science 340, 1311 (2013).