Effects of Surface Modifications on the Excited-state Properties of Silicon Quantum Dots and Silicon Nanowires, A Multi-level Theoretical Study

Silicon (Si) nanostructures are the most attractive nanomaterials for optoelectronics, because of the well-established Si technology. This research team is actively engaged in both growth control of Si nanowires (SiNWs) and exploring their applications. However, a number of issues related to luminescence mechanisms and the effects of surface species on optical properties still need further understanding and investigation.This project aims to systematically study the excited-state properties and resolve the signatures in optical absorption and emission of Si quantum dots and SiNWs with and without surface modifications. The study will be conducted using multilevel theories including conventional time-dependent density-functional theories and a new approach based on optimized effective potential. Species/molecules containing H, C, N, O, and F of chemical and/or biological importance will be considered for the surface modification. Particular attention will be paid to the excited-state relaxation and other physical processes including indirect-to-direct band gap transition, and tuning of fluorescence yield due to surface modifications. The results will provide the needed understanding of the luminescence mechanisms of Si nanostructures, which will facilitate their application in optoelectronics and chemical/biological sensing.