Past Events

Abstract

Optical and electrical properties of solids have a close relationship with their dimensionalities. In this public seminar, optical properties of several direct bandgap semiconductors with different dimensionalities will be presented. In three dimensional bulk zinc oxide (ZnO) single crystal, two-electron-satellite (TES) transition of bound excitons was examined in terms of a radiative Auger effect. On the basis of experimental spectral data, a model was proposed to interpret temperature dependence of its integrated intensity. Being as a new family of two dimensional materials, monolayers of transition metal dichalcogenides (TMDCs) have received an increasing research interest in the past few years because of the bandgap nature transition from the indirect band gap of bulk to the direct bandgap of two-dimensional monolayers. Light emission properties of tungsten sulfide (WS₂) monolayers were characterized by using excitation-power dependent photoluminescence (PL) technique. Two kinds of emission mechanisms, namely band-edge free excitonic transition and localized-states ensemble emission, were revealed in mechanically exfoliated WS₂monolayers. Meanwhile, PL and Raman mappings were conducted on WS₂monolayers. It is found that the relative intensity of inter-plane vibration mode with respect to in-plane mode is critical for monolayer identification with Raman spectroscopic technique, and PL mapping can yield more information on the uniformity and quality of the samples. In the last part of the seminar, optical properties of WS₂nanotubes, ZnO nanorods and GaN nanopillar array are reported. WS₂nanotubes were found to show interesting Raman light scattering features, while ZnO nanorods prepared by vapor phase transport method were revealed to have distinctive light emission properties. Surface vibration mode was firmly demonstrated to exist in these nanostructures with optical studies and theoretical analysis.

Anyone interested is welcome to attend.