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Controlling The Growth Direction of ZnO Nanowires (NWs) on c and a -Plane Sapphire

Babak Nikoobakht a, Albert Davydov b and Stephan J. Stranick a

a Surface and Microanalysis Science Division, CSTL

b Metallurgy Division, MSEL

Abstract

The issue of controlling the growth direction of NWs is vital in nanotechnology applications and future optoelectronic devices. In an effort to address the above, we have begun studies aimed at selectively controlling the growth direction of horizontal, tilted and vertical ZnO NWs. These NWs are grown via a vapor-phase transport process using an Au thin film catalyst. The two most important factors in controlling the growth direction are found to be the substrate crystal structure and the Au catalyst morphology. On c-plane sapphire, we have found that by controlling the thickness of the Au-film and pre-growth annealing of the Au/sapphire substrate, NWs can be grown either tilted or vertical. We have concluded that annealing alters the sapphire surface termination from Al to O, which results in change of the NW growth direction from tilted to vertical. For growth of horizontally aligned NWs on a-plane sapphire, our results show that the size and packing density of Au nanodroplets are critical in obtaining the observed growth direction. Au nanodroplets smaller than 20 nm result in growth of horizontal NWs, conversely, nanodroplets larger than 20 nm result in the growth of standing NWs. These results will be discussed along with atomic force microscopy (AFM), scanning electron microscopy (SEM) and XRD analysis of the prepared nanostructures.

Presenting author: Babak Nikoobakht

Division: 837.03, Chemical Science and Technology Laboratory, Rm:A19, Bldg221, Mail stop:8372, Phone:301-975-3230, Fax: 301-926-6689, e-mail: babakn@nist.gov

Category: Materials