Pulsed cathodoluminescence and Raman spectra of MoS2 and WS2 nanocrystals and their combination MoS2/WS2 produced by self-propagating high-temperature synthesis

Abstract

Molybdenum and tungsten disulfide nanoplates were produced by self-propagating high-temperature synthesis in argon atmosphere. This method provides an easy way to produce MoS2 and WS2 from nanoplates up to single- and several layers. The Raman peak intensities corresponding to in-plane E12g and out-of-plane A1g vibration modes and their shifts strongly depend on the thicknesses of the MoS2 and WS2 platelets indicating size-dependent scaling laws and properties. An electron beam irradiation of MoS2 and WS2 powders leads to an occurrence of pulsed cathodoluminescence (PCL) spectra at 575 nm (2.15 eV) and 550 nm (2.25 eV) characteristic to their intrinsic band gaps. For the combination of MoS2 and WS2 nanopowders, a PCL shoulder at 430 nm (2.88 eV) was observed, which is explained by the radiative electron-hole recombination at the MoS2/WS2 grain boundaries. The luminescence decay kinetics of the MoS2/WS2 nanoplates appears to be slower than for individual MoS2 and WS2 platelets due to a spatial separation of electrons and holes at MoS2/WS2 junction resulting in extension of recombination time.