Dislocation structure of a defective near-surface skin layer inV2H

Abstract

Here we present a detailed analysis of the depth-dependent dislocation substructure responsible for the graded defective ``skin layer'' in single crystal ${\mathrm{V}}_{2}\mathrm{H}$ whose phase transition appears continuous (tricritical) in this skin layer and strongly first order in the bulk. A skin layer with an effective thickness of 5--10 \ensuremath{\mu}m is located just below the surface of a \ensuremath{\sim}1-mm-thick bulk crystal. Within this skin, the conventional mosaic spread (x-ray rocking curve) shows a full width at half maximum that decays into the bulk. In this paper, we determine, via diffuse scattering distribution in the vicinity of the Bragg points, the dislocation arrangement and its associated stress field. The results can then be used in interpreting the influence of this stress field on the change of the order of the phase transition as well as in the discussion of the two-length scale pattern where both length scales show a critical behavior.