A low-temperature evaporation route for ZnO nanoneedles and nanosaws

A low-temperature (550 degreesC) catalyst-free route has been applied to fabricate ZnO nanoneedles and nanosaws via evaporation of metallic Zn powder. The nanoneedles are vertically aligned on GaN(0001)/Si(111) substrates. Based on electron-microscopy observations, we postulate that the needles grew from the closely stacked ZnO columnar grains, which were formed with [0001] texture in an early stage. The uniquely shaped ZnO nanosaws were found in a large quantity under a similar low-temperature growth condition. In addition, single-crystalline micrometer saws were also obtained under an increased Zn vapor supersaturation by changing the sample configuration.