Optical properties of ultra small Si nanoparticles: potential role of surface reconstruction and oxygen contamination

Abstract

We report accurate high level calculations of the optical gap and absorption spectrum of ultra small Si nanocrystals, with hydrogen and oxygen passivation, (with and without surface reconstruction). Our calculations have been performed in the framework of time dependent density functional theory (TDDFT) using the hybrid nonlocal exchange and correlation functional of Becke and Lee, Yang and Parr (B3LYP) and the multireference second-order perturbation theory (MR-MP2). We show that some of the details of the absorption and emission properties of the 1 nm Si nanoparticles can be efficiently described in the framework of TDDFT/B3LYP, by considering the effect of surface reconstruction and the geometry relaxation of the excited state. Additionally, we have examined the effect of oxygen contamination on the optical properties of 1 nm nanoparticles and its possible contribution to their experimentally observed absorption and emission properties.