  The redshifts and asymmetric broadening observed in nanocrystal Raman Spectra
are attributed to the quantum confinement effects by some authors. But others
show that they may come from the local heating caused by the incident laser as
well. In this study we demonstrate that in the Si nanocrystal case the latter
at most has obvious effects on the broadening but has negligible effects on the
1LO peak shift, while the former contributes most of the 1LO peak shift. We
also demonstrate that after assigning appropriate interatomic force constants
in the calculation of Raman Spectrum by bond polarizability approximation model
within the regime of free boundary condition, we may acquire the matching 1LO
peak shift with experiments.
