Defect studies in crystals by means of channeling

Abstract

Channeling of fast, light ions (e.g. protons and α particles) in crystals containing displaced atoms is discussed on the basis of Lindhard's theory, with the particular purpose of applying channeling as a tool for studying crystal defects. Measurements of the orientation dependence of the yield of close-encounter processes, such as nuclear reactions and wide-angle elastic scattering, can provide information about the depth distribution of structural defects in the first few microns beneath the surface of a single crystal. The relation between the yield and defect concentration is derived. This relation has led to a new double-alignment technique that combines channeling and blocking, and increases considerably the sensitivity for detecting structural defects.Scattering yield measurements in tungsten and silicon crystals covered with amorphous oxide layers of accurately known thickness are used to verify the results of the theoretical discussion. Double alignment is demonstrated. Criteria for selecting the optimal experimental conditions are set up. The sensitivity of the method for detecting lattice disorder corresponds to the displacement of ~1014–1015 atoms per cm2 (i.e. less than one atomic layer); the depth resolution with which, for example, radiation damage may be determined is ~50 Å.