Raman spectroscopy of ZnS nanostructures

We report Raman scattering results of wurtzite ZnS nanowires, nanocombs, and nanobelts. The Raman spectrum obtained from ZnS nanowires exhibits first‐order phonon modes at 272, 284, and 350 cm⁻¹, corresponding to A₁/E₁ transverse optical, E₂ transverse optical, and A₁/E₁ longitudinal optical phonons, respectively. Several multiphonon modes are also observed. The longitudinal optical phonon mode varies in wavenumber for nanocombs and nanobelts, indicating that the residual strain varies during the morphological change from ZnS nanowires to nanocombs and ultimately to nanobelts. Interestingly, a surface optical (SO) phonon mode varies in wavenumber depending on the shape and surface roughness of the ZnS nanostructures. The surface modulation wavelengths of the ZnS nanowires, nanocombs, and nanobelts are estimated using the SO phonon dispersion relations and the observed SO phonon wavenumbers. Copyright © 2012 John Wiley & Sons, Ltd.     

Size dependence of surface optical mode and electron–phonon coupling in ZnO nanocombs

ZnO nanocombs with different sizes are synthesized by simple thermal evaporation methods. Scanning electron microscopy and transmission election microscopy testify the growth of single crystal ZnO nanocombs along [0 0 0 2] direction. The temperature-dependent Raman spectra show that the intensity of surface optical (SO) modes in ZnO nanocombs obviously increases with declining measure temperatures. With the decrease of diameters, the frequency of SO modes shows a blue shift due to the passivation of surface states. The resonant Raman scattering shows that the strength of electron–phonon coupling increases with decreasing size. Calculated on size-dependent electron–phonon interaction energy agrees well with measured values for a large size range. The origin of electron–phonon coupling in ZnO nanocombs is also discussed.