Visible Photoluminescence from Size-Dispersed Si Nanoparticle Films

We produced silicon nanoparticles with diameters from 1 to 20 nm by laser ablation of Si in He mbient gas and extracted them into a vacuum as a cluster beam. Using a technique of crossing an Ar molecular beam perpendicularly to the silicon cluster beam before deposition on a substrate, we synthesized size-dispersed Si nanoparticle films. These size-dispersed nanoparticle films exhibited visible photoluminescence (PL) after exposure to air. The peak PL energy was shifted from 1.42 to 1.72 eV when the average diameter of the surface-oxidized nanoparticles deposited in the film changed from 10 to 3 or 4 nm. At positions that we expected to have particles smaller than 3 or 4 nm, however, we observed no further blue shift of the peak PL energy. In this paper, we discuss mechanisms of the size-dependent PL of the surface-oxidized Si nanoparticles.