Published online by Cambridge University Press: 01 February 2011
Nanoindentation studies were conducted on a-axis oriented ZnO single crystals. The mechanical properties and deformation mechanisms were monitored and compared to previously determined data from c-axis material. Hardness and modulus values reveal that a-axis ZnO is significantly softer than c-axis material (measured hardness of 2 ± 0.2 GPa) and behaves much more plastically. Additionally, the influence of contact induced damage upon the defect structure of a-axis material was also examined using cathodoluminescence spectroscopy and monochromatic imaging to monitor the luminescence from indent sites. Deformation directly under the indent site enhanced the occurrence of red defect luminescence, and was attributed to a native defect in ZnO that has a higher formation energy than the defects responsible for the green and yellow visible defect bands, which were present in the ZnO during growth and were found to cluster to the indent site during annealing.