Quantum confinement and thermal effects on the Raman spectra of Si nanocrystals

In nanocrystals, first-order Raman spectra can exhibit large shift and width due to two overlapping effects: quantum confinement and thermal heating. In order to distinguish each contribution we studied silicon nanocrystals by Raman spectroscopy. From the measurements we extracted the dependence of the Raman shift and width as a function of the temperature. A model size and temperature dependence was developed for the interpretation of these data, demonstrating the negligible contribution of the quantum confinement for sizes higher then 6 nm. Excellent agreement between theory and experiment was obtained both for the energy shift and for the width broadening.