Bremsvermögen in Kristallkanälen

To characterize bulk properties of single crystals (e.g. lattice sites of dopants, crystal damage, lattice spacing of strained layers) medium energy ion scattering (MEIS) is still an unrivaled technique: helium ions are directed onto a crystal in a low index direction, leading to channeling, and the backscattering yield provides the relevant information. To interpret MEIS spectra one depends on Monte Carlo simulations of the projectile trajectories within the target. An indispensable quantity for simulations is the specific energy loss of channeled projectiles. However, there are no theories which can predict the specific energy loss within channels. Also, experimental data are very scarce and mainly confined to silicon: there are only few materials out of which thin selfsupported monocrystalline targets can be made which are necessary in usual transmission experiments. Recently, Hetherington (NIM B90 [1994] 84) has managed to measure energy loss in channels in backscattering geometry. We will essentially improve his method using a backscattering assembly developed in our institute which allows us to vary the scattering angle of the detected projectiles between true 180 and 177. By this we want to determine the specific energy loss of swift light ions in channels. This is an extension of our long-standing investigation of random stopping power. The project will be performed in close cooperation with the solid state groups at our university (G. Bauer, H. Heinrich, W. Jantsch) to provide by MEIS measurements answers to questions of immediate interest in solid state physics.