Optical phonons in the bulk and on the surface of ZnO and ZnTe/ZnO nanowires in Raman spectra

Raman spectra of ZnO and core-shell ZnTe/ZnO nanowires have been measured under conditions of nonresonant and resonant excitations by Ar+ and He-Cd lasers. The optical vibration frequencies that are characteristic of the wurtzite structure of ZnO crystals have been determined. The Raman-active longitudinal optical (LO) phonons in all the studied structures have a mixed A (1) and E (1) symmetry. Surface optical modes with frequencies of 460-470 cm(-1) have been found. Surface optical modes of single-layer nanowires have been analyzed using the calculation performed in the previous work by P.M. Chassaing and his colleagues, and those of double-layer nanowires have been analyzed in terms of the expressions obtained in the present work. The size of heterogeneities of the nanowires along their axis has been determined.