High resolution, two-dimensional image mapping of ZnO nanowires by confocal microphotoluminescence and microraman spectroscopy.

High-quality ZnO nanowires were synthesized using both Au catalysts and ZnO seeds by chemical vapor depositionon basal plane sapphire substrates. The nanowires were hexagonal and aligned with their c-axis closely perpendicular to the sapphire substrate surface. The structural characteristics of the nanowiresgrown using the different catalysts/seeds were compared using scanning electron microscopyand X-ray diffraction. Their optical properties were assessed using microphoto-luminescence and confocal microRaman spectroscopy and compared. The nanowires exhibited a strong near band-edge related UV luminescence emission along with a defect related visible emission. The dependence of the luminescence as a function of incident excitation power and depth along the axis of the nanowires was studied. The wurtzite structure of the ZnO was confirmed from the Raman measurements. Two-dimensional mappings of the microphotoluminescence emission at different wavelengths and microRaman scattering from the nanowire samples were carried out using a confocal laser scanning microscope. This enabled the ability to correlate the near band-edge UV and visible emissions over the mapped area.