High resolution transmission ion channeling investigations of crystal defects

Abstract

The channeling effect causes a reduced energy loss rate of ions passing through a crystalline material along a major lattice orientation. Crystal defects locally disrupt the channeling process and therefore affect energy loss of channeled ions. This thesis aims to study features of crystal defects using transmission ion channeling, to simulate enhanced channeling and dechanneling effects caused by crystal defects and to provide explanations of observed channeling and blocking phenomena. Transmission ion channeling analysis of crystal defects have been performed on the NUS nuclear microscope and computer simulations have been performed on an adapted version of the Monte-Carlo channeling code FLUX7.For stacking faults in silicon, transmission channeling images are produced with different beam tilts to the (011) planes. Periodic intensity variations are observed across the stacking fault. Horizontal line scans applied across the center of the fault show these variations. The intensity oscillation wavelength is measured. For 60A? misfit dislocations in Si0.95Ge0.05/Si, transmission channeling images show asymmetrical contrast changes at various beam tilts to the (110) planes. Vertical line scans applied across the misfit dislocations show these asymmetrical contrast changes.Detailed computer simulation is used to study the origin of these enhanced channeling and dechanneling effects observed at stacking faults and 60A? misfit dislocations. Interactions of the phase-space distributions with the displaced phase-space ellipses provide a good interpretation of all observed blocking to channeling phenomena.Transmission ion channeling is combined with the ion beam induced secondary electron imaging technique. This newly combined technique is used to obtain secondary electron images of crystal defects with sufficient data statistics in a short data acquisition time of tens of seconds, compared with 10-30 minutes using the conventional approach.This thesis demonstrates that by improving data statistics and image contrast, high-resolution images of crystal defects can be obtained using transmission ion channeling. A phase-space model, which simplifies the representations of crystal defects, and horizontal and vertical displacements can be used to explain effects of ion channeling and dechanneling.