Positron re-emission microscopic images of 150nm-thick self-supporting monocrystalline (100) films were found to exhibit high-contrast band-like features at a scale of a few . Transmission electron microscopic images of the films revealed no individual features, at the -scale, that would give rise to positron trapping or strong scattering by impurities. An examination of the surfaces, using scanning electron microscopy, revealed no surface compositional variations that could be related to the positron re-emission microscopic images. At a magnification of 10000, transmission electron microscopy revealed -scale domains which contained dislocation densities of the order of 109/cm2, as compared with domains which had dislocation densities of about 107/cm2 or less. Although the lateral size of the individual dislocations was less than 100nm, the net effect of a high dislocation density was proposed to be the contrast mechanism that was responsible for the -scale dark regions which were observed in positron re-emission microscopic images. The correlation of -scale patterns in positron re-emission microscopic images, with dislocation densities, was considered with regard to the provision of focusing targets for 50000x positron re-emission microscopic studies of mono-vacancies.

K.F.Canter, G.Amarendra, D.Vasumathi, S.A.Wesley, R.Xie, A.P.Mills, R.L.Sabatini, Y.Zhu: Applied Surface Science, 1995, 85, 339-44