THE OBSERVATION OF THE LOW-FREQUENCY ACOUSTIC-PHONON TORSIONAL MODES IN NANOCRYSTALLINE SILICON

Low-frequency Raman spectra of the porous structure formed on C+-impla nted silicon were examined using the 514.5 and 488 nm lines of Ar+ las er. The sharp low-frequency Raman peaks were observed with narrow line width and large intensity. According to usual vibration theory of the elastic body and related symmetry analysis, they are identified as the localized acoustic phonon torsional modes resulting from the surface vibrations of quasifree Si nanocrystals with nonspherical shapes. (C) 1998 American Institute of Physics.