Synthesis and Raman spectra of hammer-shaped ZnO nanostructures via thermal evaporation growth

Hammer-shaped ZnO nanostructures were synthesized on silicon substrate via a simple thermal evaporation process without catalysts or additives. Scanning electron microscopy results shows that ordered ZnO nanohammers grow from the Si substrate. Transmission electron microscopy and selected area electron diffraction analysis indicate that a single nanohammer is a single crystal and grows along (0001) direction. X-ray diffraction patterns for prepared samples are consistent with a wurtzite ZnO structure. The effect of temperature on Raman scattering of single crystal ZnO nanohammers in the temperature range from 83 to 523 K was determined. Temperature-dependent Raman spectra of E2(high frequency or hf) exhibit phonon frequency redshift and linewidth broadening with increasing temperature, which can be explained by a model taking into account contributions of thermal expansion and anharmonic phonon processes. Results show that decay into three phonons is the probable channel for the E2(hf) mode.