Catalyst-free synthesis of ZnO nanorods on metal substrates by using thermal chemical vapor deposition

We report successful synthesis of ZnO nanorods on metal (Cr)-deposited Si substrates in a thermal chemical vapor deposition (CVD) process via a self-catalytic mechanism at relatively low growth temperatures of 400 and 500 degrees C. The nanotips were densely grown onto the Cr layer while ZnO nanorods with low density were synthesized on the same substrates. Grazing-incident wide-angle X-ray scattering measurements showed a uniform distribution and a random directionality of the nanotips and the nanorods grown on Cr-deposited Si substrates. Free-exciton emission from the nanorods was clearly observed from the samples at a very low temperature of 50 K in the photoluminescence measurements. In addition, strong free exciton and relatively weak deep level emission bands were detected from both samples even at room temperature, indicating the ZnO nanotips and nanorods on Cr/Si substrates in this work had a low defect density.