Growth and photoluminescence of oriented MoSe2 nanosheets produced by hot filament CVD

Abstract

In this work, we report that oriented MoSe₂ nanosheets with varying layers and structures can be synthesized on silicon substrates by hot filament chemical vapour deposition in a nitrogen environment using MoO₃ and Se powders as precursors. The results of field emission scanning electron microscopy, X-ray diffractometry, X-ray fluorescence spectroscopy, transmission electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy indicate that the layer-structured MoSe₂ nanosheets grow in a tilted direction with respect to the substrate. Beginning from the evaporation of MoO₃ and Se powders, the formation mechanisms of the MoSe₂ nanosheets are studied through the characterisation of samples produced under different conditions. Diffusion and thermal effect theory is used in conjunction with the microanalysis. The analysis suggests that the oriented growth is a consequence of stress during the formation of the MoSe₂ nanosheets and the diffusion of precursor species under an electric field near the edges of MoSe₂ nanosheets due to the charge transfer from Mo to Se atoms. The photoluminescence (PL) properties of the grown MoSe₂ nanosheets were studied and feature PL bands at about 785 nm. Compared to the PL bands of monolayer MoSe₂ sheets, the PL bands of the oriented MoSe₂ nanosheets are blue shifted. This possibly originates from the bandgap expansion of the oriented MoSe₂ nanosheets. These results are important for understanding the growth mechanisms of low-dimensional materials, controlling their growth and based on their optical performance contribute to the development of optoelectronic devices of MoSe₂-based nanomaterials.