Rongfu Li

First principles study of CdSe quantum dots: Stability, surface unsaturations, and experimental validation

Ab initio computational studies were performed for CdSe nanocrystals over a wide range of sizes and topologies. Substantial relaxations and coordination of surface atoms were found to play a crucial role in determining the nanocrystal stability and optical properties. While optimally (threefold) coordinated surface atoms resulted in stable closed-shell structures with large optical gaps, suboptimal coordination gave rise to lower stability and negligible optical gaps. These computations are in qualitative agreement with recent chemical etching experiments suggesting that closed-shell nanocrystals contribute strongly to photoluminescence quantum yield while clusters with nonoptimal surface coordination do not.Ab initio computational studies were performed for CdSe nanocrystals over a wide range of sizes and topologies. Substantial relaxations and coordination of surface atoms were found to play a crucial role in determining the nanocrystal stability and optical properties. While optimally (threefold) coordinated surface atoms resulted in stable closed-shell structures with large optical gaps, suboptimal coordination gave rise to lower stability and negligible optical gaps. These computations are in qualitative agreement with recent chemical etching experiments suggesting that closed-shell nanocrystals contribute strongly to photoluminescence quantum yield while clusters with nonoptimal surface coordination do not.

Quantitative evaluation of bundling effect on single walled carbon nanotubes by resonance Raman spectra

The radial breathing mode (RBM) region of the resonance Raman spectra of HiPco single walled carbon nanotubes (SWNTs) was investigated as a function of aggregation. This was modeled using an energetic deviation term (Δ E ), imparted to the optical transitions ( E ii ( n, m )) by bundling effect. E ii ( n, m ) values obtained from photoluminescence (PL) measurements were used to reconstruct these RBM profiles. The simulation revealed that the PL-determined E ii ( n, m ) set provided a good fit in terms of peak position. Providing an accurate set of E ii ( n, m ) values becomes available, the RBM profile reconstruction methodology discussed herein could greatly enhance our ability to model a range of physicochemical changes to the immediate environment of SWNTs.