Charge Transfer Mediated Photoluminescence Engineering in WS2 Monolayers for Optoelectronic Application

Optical emissions from two-dimensional transition metal dichalcogenides greatly differ from sample to sample due to their interactions with different substrates with variations in parameters such as the dielectric constant, absorption coefficient, growth conditions, strain, and defects. Often, the mechanisms of environmentally sensitive optical emission in 2D materials are lacking, and it is essential to perform the measurements on the same sample with different substrate backgrounds, which is a challenge. In this work, we explore photoluminescence engineering by comparing the optical properties of WS2 on SiO2, TiOx, and Pt by selectively creating different environments locally on the same sample. The PL-confocal map with good spatial resolution reveals that the emission of WS2 on TiOx and Pt is suppressed by charge transfer at the interface. While moving from WS2 on Pt toward WS2 on the TiOx region, a 3-fold enhancement in PL emission has been observed in agreement with a 20% increase in the trion-to-exciton ratio and calculated carrier densities. Further, the transient absorption spectroscopy shows faster exciton recombination in WS2/Pt (similar to 5.7 ps) and WS2/TiOx (similar to 7.2 ps) than WS2/SiO2 (similar to 48.5 ps), confirming the charge transfer in varied optical emission of the WS2 monolayer. Our method paves the way for using charge transfer and controlled carrier injection to design nanoantennas, optoelectronic devices, and quantum optical cavities in 2D materials.