Dislocation generation at surfaces of tin single crystals

Abstract

Single crystals of 99.999% purityβ-tin grown from the melt were shown by X-ray topography to contain dislocations with Burgers vectors of [001] type and of 1/2〈111〉 type. Specimen plates cut roughly parallel to (311) were chemically thinned from 1.25 mm to 100μm thickness and in two cases characteristic dislocation structures were generated at their surfaces. A specimen thinned in concentrated HCl possessed stress-producing centres distributed on its surfaces with a density of about 75 mm−2 from which regular helices and coaxial prismatic loops with [001] Burgers vector were generated together with irregular loops of 1/2〈111〉 Burgers vector dislocations. In one specimen thinned in a H3PO4, CH3COOH, HF and HNO3 mixture large arrays of pure edge dislocations grew parallel to the surface at a depth of 2 to 4μm below it, the individual dislocations extending at about 1μm h−1 during several weeks. These edge arrays all had that one of the four 1/2〈111〉-type Burgers vectors which made the smallest angle (5°) with the surface. The Burgers vector sense, determined by X-ray diffraction contrast, corresponded to a sheet of vacancies lying between the dislocation line and the surface.