Abstract
Vapor-phase growth of large-area two-dimensional (2D) MoS2 nanosheets via reactions of sulfur with MoO3 precursors vaporized and transferred from powder sources onto a target substrate has been rapidly progressing. Recent studies revealed that the growth yield of high quality singlelayer (SL) MoS2 is essentially controlled by quite a few parameters including the temperature, the pressure, the amount/weight of loaded source precursors, and the cleanup of old precursors. Here, we report a dispersive growth method where a shadow mask is encapsulated on the substrate to ‘indirectly’ supply the source precursors onto the laterally advancing growth front at elevated temperatures. With this method, we have grown large-area (up to millimeters) SL-MoS2 nanosheets with a collective in-plane orientation on c-plane sapphire substrates. Regular ripples (~1 nm in height and ~50 nm in period) have been induced by laser scanning into the SL-MoS2 nanosheets. The MoS2 ripples easily initiate at the grain boundaries and extend along the atomic steps of the substrate. Such laser-induced ripple structures can be fundamental materials for studying their effects, which have been predicted to be significant but hitherto not evidenced, on the electronic, mechanical, and transport properties of SL-MoS2.
Highlights
MoS2 atomic layers grown by chemical vapor deposition (CVD) on c-plane sapphire substrate at 950 °C. (a) Optical image, (c) Raman spectrum, and (e) PL and absorbance of a MoS2 sample grown by the dispersive method. (b) Optical image, (d) Raman spectrum, and (f) PL and absorbance of a MoS2 sample grown by the conventional direct method
It has been proposed that periodic ripple structures can be fabricated by putting or growing SL nanosheets on a wavy substrate[26,30], e.g., for bandgap engineering[26], no experimental work on generating SL-MoS2 ripple structures has been reported in the literature
MoO3 and S powders, the same as previous work[20], were used as the precursors in the CVD growth; we have introduced a shadow mask to partly encapsulate the surface of the substrate to generate the dispersive growth
Summary
MoS2 atomic layers grown by CVD (using S and MoO3 powders as the reaction precursors) on c-plane sapphire substrate at 950 °C. (a) Optical image, (c) Raman spectrum, and (e) PL and absorbance of a MoS2 sample grown by the dispersive method. (b) Optical image, (d) Raman spectrum, and (f) PL and absorbance of a MoS2 sample grown by the conventional direct method. Ripple structures, which have been theoretically predicted to have remarkable effects on the electronic and mechanical properties of SL-MoS225,26, have so far only been observed and investigated by transmission-electron microscopy in suspended SL-MoS2 nanosheets prepared by exfoliation[27,28]. Raman scattering and photoluminescence (PL) spectroscopy as well as atomic-force microscopy (AFM) have been employed to compare the SL-MoS2 nanosheets and their rippling induced by laser illuminations. Both the dispersive CVD growth method and the laser-induced rippling may have important consequences in experimental and theoretical studies of SL-MoS2 and other 2D materials
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