Regarding the asymmetry of Raman peak profiles, Gao and Yin, 2017, discuss its origin in the case of Silicon nanocrystals. "The asymmetric peak broadening towards the low-frequency side of the Ramanactive mode of Si nanocrystals with the decreasing size has been extensively reported in the literatures". Gao and Yin are proposing an atomic model "to study the origin of the ubiquitous asymmetric peak on the optical phonon fundamental in the Raman spectra of Si nanocrystals". The model "revealed that the observed asymmetric broadening is mainly caused by the surface bond contraction and the quantum confinement". As asserted by Gao and Yin, "The asymmetry and broadening around the main Raman peak in symmetric stretching vibration region undoubtedly correspond to the variant of secondarystructure, which is usually considered as a surface effect of nanocrystals, and assigned as a "surface optical" phonon".