Structural and optical properties of ZnO micro-spheres and cages by oxidation of metallic Zn powder

ZnO nano-spheres and micro-sized hollow spheres/cages have been prepared on two different substrates, Si(100) and steel alloy, by a simple vapor-solid reaction method using different zinc precursors i.e.  ZnCl2 and metallic zinc powder in the presence of oxygen at different process temperatures. The morphological studies show that the deposited ZnO micro-sized hollow spheres/cages have average sizes in the range of 1-5 μm while ZnO nano-spheres vary from 200 to 500 nm. Transmission electron microscope and X-ray diffraction analysis showed a wurtzite hexagonal structure for the synthesized products which are highly crystalline and grown along the [0001] direction. The Raman spectra exhibited a characteristic ZnO wurtzite hexagonal peak at 436.9 cm−1 in the case of Si(100) substrate, while at 437 cm−1 in the case of steel alloy substrate. The room temperature photoluminescence spectra in both the cases showed a broad band in the visible region with suppressed and short UV emission indicating that these structures have more structural defects.