Controlling Porosity of Zinc and Zinc Oxide Structured Thin Films with Glancing Angle Deposition
J.M. LaForge, M.J. Brett
University of Alberta, CA
Keywords: zinc oxide, zinc, nanorod, structured thin film, GLAD, STF, ZnO, Zn, glancing angle deposition, sputtering, physical vapour deposition, PVD, porosometry, BET, absorption
Abstract:Glancing angle deposition of sputtered metallic Zn at pressures between 1.4 mTorr and 10 mTorr has produced branched, intertwined crystalline thin film structures, where surface energy and geometric shadowing appear to play significant roles in film growth. Crystallite size and shape appear to be affected by both deposition pressure, and the use of an aperture to limit flux divergence. Deposition at 2.4 mTorr without an aperture produces crystallites up to several micrometers in length with diameters around 100 nm, and as small as 10 nm. The porosity of the films can be modified with the deposition angle, and the surface area of films deposited at angles from 0° to 84° has been characterized using gas absorption porosometry. Annealing at temperatures up to 250 °C in air oxidizes Zn films into poly-crystalline ZnO with minimal changes to the overall film structure. However, oxidization does produce changes on the crystallite surface, which leads to an increase in surface area. Rotation of the chuck during deposition also affects film morphology; preliminary SEM and XRD data from this investigation will also be presented.