Synthesis and optical spectroscopy of ZnO nanowires

Single crystal ZnO nanowires with lengths and diameters ranging from 2 to 30 μm and 100 to 300 nm, respectively, have been grown by the vapor transport method on SiO2/Si substrates using Au as catalyst. Their Raman and emission properties under different excitation wavelengths have been studied at the nanoscale. Whereas Raman measurements on nanowires corroborate the well-known ZnO phonon characteristics, their photoluminescence spectra exhibit a very broad emission band, mainly in the visible region from 450 to 800 nm, which corresponds to different defect-related recombination processes. Spectrally resolved scanning near-field optical microscopy, SNOM, of single ZnO nanowires have also been performed for a direct imaging of the photoluminescence emission with high spatial resolution below 100 nm, establishing a relationship with the simultaneously acquired topography.