This research project investigates the properties of a new class of 2-dimensional nanomaterials, i.e., layered transition metal dichalcogenides, where unique electronic, optical and transport properties not observed in the bulk phase can be harvested through the control of the dimensions in nanoscale. The research team, consisting of experts in the spectroscopic characterization and computer simulation of the materials, collaborates to gain an understanding on how the variations of the physical and chemical structures can tune the material properties. The outcome of this research will be valuable to the potential optoelectronic applications of these nanomaterials. The principal investigator of this project also develops, in collaboration with an industrial partner, a training program on instrumentation, focusing on signal measurement and processing, for both undergraduate and graduate students in multiple disciplines. This effort narrows the gap between current curriculum on such topics and the instrumentation skills required in many science and engineering disciplines.
utilizes chemically synthesized titanium disulfide nanodiscs in solution as a model system. The nanodisc thickness can be controlled in chemical synthesis, varying from a few to more than ten atomic layers, and the nanodisc diameter can be varied from tens to hundreds of nanometers, providing a significant range of dimensional control in two perpendicular directions. Using these nanomaterials, the research focuses on the following specific tasks: (i) understanding how the optical transition energy and interlayer phonon of titanium disulfide nanodiscs are influenced by the variations of both the nanodisc thickness and diameter and by the photoexcitation of the charge carriers; and (ii) understanding the rates and pathways of the charge carrier relaxation and charge transfer correlated with the dimensional variation and the interfacial structure. Time-resolved pump-probe spectroscopy and electron microscopy are the main experimental tools to elucidate the structure-property relationship. The calculation of the electronic and vibrational structures of the nanodiscs of different dimensions, employing density functional theory, provides an atomistic picture of the structurally dependent material properties of this layered material system.
