Phys.org June 20, 2022
A team of researchers in the US (UT Austin, Auburn University) performed an extensive study of transient optical absorption of both W- and Mo-based single-crystalline monolayer TMDs grown by a recently developed laser-assisted evaporation method. All spectral features of the monolayers as grown on fused silica substrates exhibited appreciable redshifts relating to the existence of strain due to growth conditions. These systems exhibited a dramatic slowing down of exciton dynamics with an increase in carrier densities, which strongly contrasted with the monolayers in their freestanding form as well as in comparison with more traditionally grown TMDs. The observations were related to the modifications of the electronic bands as expected from the strain and associated population of the intervalley dark excitons that could now interplay with intravalley excitations. These findings were consistent across both the Mo- and W-based TMD families, providing key information about the influence of the growth conditions on the nature of optical excitations and fostering emerging optoelectronic applications of monolayer TMDs…read more. TECHNICAL ARTICLE