Raman investigation of silicon nanocrystals: quantum confinement and laser-induced thermal effects

We present a detailed experimental and theoretical Raman investigation of quantum confinement and laser-induced local thermal effects on hydrogenated nanocrystalline silicon with different nanocrystal sizes (3.6–6.2 nm). The local temperature was monitored by measuring the Stokes/anti-Stokes peak ratio with the laser power density range from ~120 to 960 kW/cm2. In combination with the three-dimensional phonon confinement model and the anharmonic effect, which incorporates the three-phonon and four-phonon decay processes, we revealed an asymmetrical decay process with wavenumbers ~170 and 350 cm–1, an increasing anharmonic effect with nanocrystal sizes, and a shortening lifetime with enhanced temperature and decreasing nanocrystal dimension. Furthermore, we demonstrated experimentally that for Si nanocrystals smaller than 6 nm, the quantum confinement effect is dominant for the peak shift and line broadening. Copyright © 2011 John Wiley & Sons, Ltd.

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