Crystalline orientation control in sol–gel preparation of CuAlO2 thin films

Abstract

Thin films of CuAlO2 were prepared by the sol–gel method using Cu acetate and Al acetate as starting materials. Films prepared using a sol with a total metal ion concentration of 0.40 M and gel preparation conditions with a post-coating heat treatment higher than 400 °C displayed crystallinity with significant c-axis orientation after annealing at 850 °C in N2. Almost no X-ray diffraction peaks beside the c-axis-oriented peaks were observed. In contrast, films prepared using a sol with higher metal ion concentration showed non-c-axis-oriented X-ray diffraction peaks of CuAlO2 in addition to c-axis-oriented peaks. It is found that dip-coating using a sol with an adequately low total metal ion concentration followed by post-coating heat treatment at an adequately high temperature produce the gel films that contain microcrystalline CuO. It is considered that the gel films that contains microcrystalline CuO with sufficiently thin thickness are appropriate to produce significantly c-axis-oriented CuAlO2 films after high-temperature annealing under nitrogen flow.