  Synthesis of large-scale, uniform, easily transferable, and highly
crystalline monolayer (1L) molybdenum disulfide (MoS2) on different substrates
is a challenge and could decide its suitability for opto-electronic device
applications. Herein, we report a facile NaCl-assisted Chemical Vapor
Deposition (CVD) synthesis of high-quality MoS2 on amorphous, crystalline and
layered substrates. Optical microscopy and Raman spectroscopy show that
sapphire and SiO2/Si are suitable substrates for large 1L-MoS2 flakes growth,
while mica is excellent for large-area continuous films. Comparatively lesser
full-width-at-half-maximum (FWHM) of predominant A exciton peak (which is
associated with direct band gap at K point) in photoluminescence spectra of
1L-MoS2 on sapphire suggests its high crystalline quality. However, 1L-MoS2 on
other substrates, especially on quartz and bare Si show poor crystalline
quality. The study depicts that the NaCl assists in the formation of seeding
promoter such as water-soluble layer of Na2S and/or Na2SO4 on the substrate
that helps in 2D planar nucleation of MoS2. The formation of such intermediate
seeding layers also helps in layer transfer owing to its easy water solubility.
The study could be utilized for large-scale synthesis of 1L-MoS2 on different
substrates for high-performance optoelectronic devices.
