Phonon confinement in oxide-coated silicon nanowires

Raman spectroscopy of micron-long crystalline Si nanowires covered with a thick SiO2 layer showed a downshift and asymmetric broadening of the Raman first order TO phonon peak when compared with the bulk (q=0) mode. The Raman shift and broadening were attributed to phonon confinement in the nanowires. A phenomenological phonon confinement model, incorporating the effects of nanowire diameter distribution, is presented. This model is shown to accurately describe the broadening of the Raman peak and is consistent with the microstructure of Si nanowires. In addition to the work a distribution of the phonon wave vector was directly taken into consideration replacing the diameter distribution to fit the Raman TO peak. The effects of the nano-Si:SiO2 boundary on the Raman spectra are discussed in terms of softening of the phonon confinement. (C) 2004 American Institute of Physics.