Abstract: Transition metal dichalcogenides (TMDs) have recently emerged as atomically thin semiconductors whose application to optoelectronics motivates a detailed understanding of their fundamental carrier dynamics. The inherent spatial heterogeneity of these materials, however, begets the need to address their ultrafast dynamics on the nanoscale. To this end, we have interfaced a photoemission electron microscope with a megahertz repetition-rate fiber laser to resolve the dynamics of spatially heterogeneous materials with ~50-fs time and ~50-nm spatial resolution. In the case of TMDs, our studies by time-resolved photoemission electron microscopy reveal spatial variations in the rates of electronic relaxation, carrier recombination, and electron transfer.

Bio: Zhi-Heng Loh received his S.B. in Chemistry from Massachusetts Institute of Technology before embarking on his Ph.D. studies at the University of California, Berkeley. His group is focusing on the ultrafast coherent electronic and vibrational dynamics of molecules and nanoscale materials. More recently, these efforts have expanded to include the investigation of the ultrafast carrier dynamics of 2-D materials at the nanoscale.