Effect of atmospheric oxidation on the electronic and photoluminescence properties of silicon nanocrystals

Web-like aggregates of coalesced Si nanocrystals produced by a laser vapori zation-controlled condensation technique show luminescence properties that are similar to those of porous Si. The results are consistent with a quantu m confinement mechanism as the source of the red photoluminescence (PL) in this system. The oxidized Si nanoparticles do not exhibit the red PL that i s characteristic of the surface-oxidized Si nanocrystals. The nanoparticles are allowed to oxidize slowly, and the PL is measured as a function of the exposure time in air. A significant blue shift in the red PL peak is obser ved as a result of the slow oxidation process. The dependence of quantum si ze effects on the bonding structure is established by correlating the PL da ta with the photon-yield electronic structure measurements made at the Adva nced Light Source. The results indicate that as the nanoparticles oxidize, the radius of the crystalline core decreases in size, which gives rise to a larger bandgap and consequently to the observed blue-shift in the PL band. The correlation between the FL, SXF, and NEXAFS results provides further s upport for the quantum confinement mechanism as the origin of the visible P L in Si nanocrystals.