Growth and Raman spectroscopy of ultrathin ZnO(0001) films on Ag(001)

•Ultrathin ZnO(0001) films were investigated by XPS, LEED and Raman spectroscopy.•ZnO(0001) films are characterized by two domains rotated by 30°.•ZnO film Raman spectra is significantly modified as compared to its bulk-counterpart.•ZnO films display substantial intensity enhancement of their Raman combination modes connected its finite-size electronic properties.•Raman modes of the ZnO film is possibly related to pre-resonant Raman scattering phenomena. The growth and vibrational properties of ultrathin ZnO(0001) films on Ag(001) were investigated by X-ray and ultraviolet photoemission spectroscopy (XPS/UPS), low-energy electron diffraction (LEED), and Raman spectroscopy. Our results indicate the formation of well-defined stoichiometry and crystalline phase ~5 ML thick ZnO(0001) films characterized by two domains rotated by 30°. Further film analysis using Raman spectroscopy showed that the ultrathin films display substantial intensity enhancement of their Raman combination modes. Our findings suggest a significant role of the finite-size film electronic and structural properties on its vibrational properties. These observations may serve as a pathway toward further investigations dependent on film thickness and orientation. More important, the modification of the vibrational properties is expected to be relevant to understanding general phenomena in ZnO nanostructures (i.e. thin films, nanoparticles, nanorods). [Display omitted]