Preparation of aluminosilicate crystalline coatings from sol‐gel derived alumina films deposited on silicon/silica substrates

Abstract

Abstract The dedicated formation of crystalline coatings of the trimorphous aluminosilicates with the composition of Al 2 SiO 5 starting from a low‐cost sol‐gel deposition of alumina thin films is reported. The influence of substrate type and film thickness on the crystallisation behaviour and film morphology is studied by means of wide‐angle X‐ray scattering (WAXS) and X‐ray reflectometry (XR). When annealed at a temperature of 1150 °C under high‐vacuum conditions, formation of the aimed phases was achieved only for films deposited on naturally oxidised Si‐substrates covered with a thin silica layer (thickness is about 3 nm). In the case of films deposited on amorphous quartz glass and thermally oxidised Si‐substrates covered with a thick silica layer (thickness is about 500 nm) no crystallisation occurred at this temperature. After annealing at the higher temperature of 1300 °C under high‐vacuum conditions, in the films deposited on both kinds of Si‐substrates mullite (Al 4 SiO 8 ) crystallises together with cristobalite (SiO 2 ) whereas the film deposited on the quartz glass substrate remains amorphous from viewpoint of WAXS. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)