%0 Journal Article
%T Probing the upper band gap of atomic rhenium disulfide layers
%J -
%D 2018
%R https://doi.org/10.1038/s41377-018-0100-3
%X Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13£¿nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57£¿eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron¨Chole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38£¿eV in the excited state that are induced by pumping from 1.57 to 1.72£¿eV are restricted because these transitions highly correlate with the forbidden d¨Cd intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38£¿eV) with wavelength-variant SHG probes (2.60¨C2.82£¿eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05£¿eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5£¿eV) using modified DFT calculations
%U https://www.nature.com/articles/s41377-018-0100-3