Orientation-dependent Raman spectroscopy of single wurtzite CdS nanowires

Orientation-dependent Raman measurements on single wurtzite CdS nanowires with an average diameter of 60 nm have been performed. The resonance Raman spectra of nanowires are compared with those of bulk ribbon. Different from the bulk sample, the intensity of most Raman bands of the nanowires are polarized along the longtitudinal axis because of the shape-induced depolarization effect, which is in agreement with the predication based on a simple dielectric contrast model and experimental results of polarized photoluminescence. The detailed angular dependencies of various Raman bands of the nanowires show-that LO features and their overtones are affected strongly by the anisotropic geometry of the nanowires while the E-2(H) band shows a distinctive angular dependence, which reflects the interplay of crystal symmetry, electronic resonance, and shape effect in relative Raman intensity. These results indicate that the anisotropic shape of CdS nanowires is a dominant factor in determining their optical properties.