Optical Properties Of Silicon Clusters Deposited On The Basal Plane Of Graphite

Abstract

AbstractLaser ablation and post annealing was employed for the synthesis of silicon (Si) clusters on highly oriented pyrolytic graphite surfaces in an ultra high-vacuum environment. The size distribution of the clusters was determined as a function of annealing time and temperature using an in situ scanning tunneling microscope (STM). Pure Si clusters with sizes ranging from 1 to 10 nm showed no detectable photoluminescence (PL) in the visible range. Exposure of these clusters to oxygen at 10−6 Torr and for up to 8 hours showed adsorption of oxygen on the surface of the clusters without Si oxide formation and no detectable PL. Hydrogen termination of these clusters was accomplished by exposing them to atomic hydrogen beam but did not result in any detection of the PL spectra either. Prolonged exposure of these clusters to ambient air, however, resulted in strong PL spectra with color ranging from red to greenish-blue depending on average cluster size. Auger electron spectra (AES) revealed the existence of partially oxidized Si clusters for these samples. This PL could be due to either an oxide phase or to quantum confined Si inner cores.