Positioning growth of ZnO whiskers/dots on sapphire substrates

Abstract

Micro-nano ZnO whiskers and dots have been selectively grown on sapphire substrate using Au/Pt catalyst arrays. The catalyst array was fabricated by employing a nanoindentation tester, which is simpler than conventional micro-nano fabrication techniques. The electric current heating (ECH) method was used to provide ZnO sources from a ZnO ceramic bar heated to about 1000 °C. The whiskers and dots were grown in the Vapor–Liquid–Solid (VLS) growth mode inside a gold image furnace. SEM images identified dramatic differences in the crystal structures grown at 940 °C, specifically, whiskers for Au catalyst and dots for Pt catalyst. Whiskers are characterized by diameters of 10 nm to sub-micron and lengths from sub-microns to tens of microns. Dots, however, have a uniform diameter of about 100 nm. We found growth beginning at the arrayed Au catalyst positions. In contrast, dots were formed, but no whiskers were observed around the Pt catalyst. These features are explained in terms of different catalyst melting points: VLS growth was realized for the Au catalyst but not for the Pt catalyst at 940 °C. Good to excellent quality ZnO whisker and dot crystals was confirmed by micro-photoluminescence (PL) measurement.