Chemical Reaction of Si Nanoparticles during Formation in Gas Phase Observed by a Time-Resolved Photoluminescence Method

We have investigated the chemical reaction of Si nanoparticles with H2 and O2 gases in gas phase after laser ablation of Si targets in Ar and Ne gases. First, we observed time-resolved photoluminescence (PL) from Si nanoparticles in pure Ar gas. The formation of Si nanoparticles begins after the thermalization of Si plasma on a time scale of 1 ms. The energy dissipation of electronic system govern the formation of Si nanoparticles. It was clearly observed that Si nanoparticles grow up to 1.8 ms. Based on the formation dynamics, we observed chemically modified Si nanoparticles using the time-resolved PL method. We found that Si nanoparticles react with hydrogen and oxygen atoms dissociated in the laser plasma. The hydrogenation results in PL at 550 nm and vibronic lines in the wavelength range of 650–800 nm disappear. Oxidation results in PL quenching when O2 partial pressure is higher than 1 Pa. Thus, we have demonstrated chemical modification of Si nanoparticles.