FORMATION OF NANOMETER-SIZE SILICON PARTICLES IN A LASER-INDUCED PLASMA IN SIH4

Crystalline silicon particles of cubic structure are formed in the pla sma which is initiated in an argon-silane mixture by a focussed 694 nm Ruby laser flash. Part of the particles can be dissolved as colloid i n organic solvents. The solubilization is increased by small amounts o f 1,3-propane-dithiol. The raw material has a broad size distribution. Centrifugation and filtration methods are applied to obtain samples w ith narrow size distribution. Small silicon particles have structured absorption spectra. The particles luminesce after etching with HF unde r air. The larger particles have a red luminescence (peaking at 720 nm ) and the smaller particles emit a blue luminesce. The luminescence ef fects are explained by size quantization of the electronic energy leve ls in the particles.