In the recent years there has been intense effort in the preparation of nano-sized thin film metal-oxides, largely due to their markedly different physical and chemical properties with respect to bulk materials. Nanocrystalline ZnO has attracted much interest due to its potential applications in solar cells, chemical sensors, pigments and rubber additives, electrical, acoustic and luminescent devices.

The microstructural characterization of r.f. magnetron sputtered ZnO thin films deposited on 6H-SiC is presented, together with a comprehensive investigation of the films properties as a function on annealing temperature and film thickness. These structures, with some modifications, are utilised as Schottky diode hydrogen gas sensors.

The films after annealing in static air at temperatures of 300, 500, 700 and 900C for 1 hour have been characterized by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS), X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) techniques. The morphology was studied by SEM which reveal the ZnO grows in cylindrical columnar grains, normal to the SiC surface, which have mean diameter of around 100-120 nm and lengths dependent on the film thickness.

XRD experiments revealed the formation of hexagonal ZnO (JCPDS card. 36-1461) was obtained by annealing the films at temperatures higher than 700C. The surface chemical composition of these films was investigated by XPS. Selected-area XPS depth profiling of the samples was carried out by using cyclic Ar+ sputtering at low ion energy. The separation of different chemical species of the same element and quantitative analysis of experimental depth profiles enabled us to completely reveal the chemical composition of the films investigated. In such a way, the samples of mixed oxides, annealed at different temperatures, were characterized and compared. The influence of the films chemical composition on the gas-sensitive properties is also discussed.

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