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Calculations have been carried out on the elastic scattering of slow positrons by krypton and xenon atoms. The polarisation potential has been obtained using a procedure based on the Pople-Schofield approximation. We present two sets of results calculated with normalised and un-normalised polarisation potentials. It is shown that the results are very sensitive to the polarisation potential used. For krypton a Ramsauer minimum is predicted when the normalised polarisation potential is used whereas no structure in the total elastic cross section is obtained with the un-normalised polarisation potential. The correlation between electron and positron scattering is discussed.

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Zinc oxide (ZnO) thin films have been grown by radio frequency sputtering on glass, Al, Au and R cut sapphire substrates. Microstructures of the ZnO / substrate interface have been observed by transmission electron microscope. The purpose of this study is to elucidate the crystal growth mechanism of ZnO thin films using various substrates that have different crystallinity and crystal structures. An amorphous layer with a thickness of about 5 nm is observed at the ZnO/glass interface, and c axis orientation perpendicular to the substrate is observed on this amorphous layer. Mianstructurts at the ZnO/buffer metal interface, on the other hand, are significantly different from those of ZnO/glass interface. A thick amorphous layer of about 15 nm is observed at the ZnO/Al interface, presumably consisting of Al2O3 interface layer material. ZnO thin film grown on Au buffer layers is distinctly different from both ZnO on glass and Al. No amorphous layer is formed at the ZnO/Au interface, and c axis orientation begins directly from the Au surface. Epitaxially grown ZnO thin film is confirmed on a R-cut sapphire substrate. These results dearly demonstrate that ZnO thin films prepared by radio frequency sputtering are strongly influenced by the substrate surface crystallinity at the topmost layer of the substrate.