An approach to control the tip shapes and properties of ZnO nanorods

High-density, well aligned, < 0001 >-oriented wurtzite ZnO nanorod arrays with significantly different tip shapes were controllably fabricated by evaporating zinc powders at temperatures varying from 450 to 600 degrees C. It is found that the tip shape depends not only on the substrate but also on the substrate direction relative to the auxiliary gas flow, and the radius of curvature at these tips can be less than 2 nm. These nanorods exhibit good rectification characteristics in conductive atomic force microscopy (CAFM) measurements; the current rectification can be as large as similar to 10(3) at 1 V. The conductance of these 'nanotips' can be tuned readily by simple air-annealing.