Abstract

Abstract A magnetic deflection system has been developed which enables the backscattering (RBS) yield to be measured within a small (0.04°) angular cone centred exactly at 180°. Using this system, we have investigated the magnitude and depth dependence of the 180° RBS yield enchancement effect. In a wide variety of targets, we obtain enhancements greater than a factor of 2; in all cases the maximum enhancement was observed not at the surface (as reported recently by Kirsch and Poizat) but at depths of 7–20 nm beneath the surface. In the case of Au, the observed enhancement was independent of temperature and hence of vibrational amplitude, over the range 300–800 K. A series of thin amorphous WO 3 films on monocrystalline W has enabled the depth dependence of the effect to be studied in considerable detail. We have also measured the scattering from Bi in a set of Bi-implanted targets (C, Si and Ge) in order to investigate the effect of medium- and low-mass substrates. The yield enhancements are large, i.e. greater than two-fold. This is in marked contrast to earlier measurements of scattering from (unimplanted) targets of low atomic mass.

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