Raman selection rule for surface optical phonons in ZnS nanobelts

Abstract

We report Raman scattering results for high-quality wurtzite ZnS nanobelts (NBs) grown by chemical vapor deposition. In the Raman spectrum, the ensembles of ZnS NBs exhibit first order phonon modes at 274 cm⁻¹ and 350 cm⁻¹, corresponding to A₁/E₁ transverse optical and A₁/E₁ longitudinal optical phonons, in addition to a strong surface optical (SO) phonon mode at 329 cm⁻¹. The existence of the SO band is confirmed by its shift with different surrounding dielectric media. Polarization dependent Raman spectra were recorded on a single ZnS NB and for the first time a SO phonon band has been detected on a single nanobelt. Different selection rules for the SO phonon mode are shown from their corresponding E₁/A₁ phonon modes, and were attributed to the breaking of anisotropic translational symmetry on the NB surface.