Solution of the inverse problem of kinematic x-ray diffraction by nonuniform crystal structures (original) (raw)

Structural changes in arsenic ion-implanted Hg1–xCdxTe epitaxial layers

Results of X-ray investigations of Hg1–xCdxТе (х = 0.25) epitaxial layers after single and two-stage arsenic ion implantation with the energy E = 100 keV are represented. It has been established that for doses D1 = 2 × 1014 ions/сm2 and D2 = (2 × 1014 + 1015) ions/сm2 the Frenkel pair (anion vacancy + interstitial mercury atom) generation is the most probable process. The model of a possible system of structural defects in the near-surface layers of ion-implanted structures Hg1–xCdxТе is proposed. The model allows for the presence of certain dimensions and concentrations of both growth and new defects – the Frenkel pairs, cluster formations and dislocation loops formed under ion radiation. The calculated deformation profiles are complex in shape with characteristic peaks at the depth of maximum nuclear power ion loss.

Model for Photoinduced Bending of Slender Molecular Crystals

The growing realization that photoinduced bending of slender photo-reactive single crystals is surprisingly common has inspired researchers to control crystal motility for actuation. However, new mechanically responsive crystals are reported at a greater rate than their quantitative photophysical characterization; a quantitative identification of measurable parameters and molecular-scale factors that determine the mechanical response has yet to be established. Herein, a simple mathematical description of the quasi-static and time-dependent photoinduced bending of macroscopic single crystals is provided. This kinetic model goes beyond the approximate treatment of a bending crystal as a simple composite bilayer. It includes alternative pathways for excited-state decay and provides a more accurate description of the bending by accounting for the spatial gradient in the product/ reactant ratio. A new crystal form (space group P2 1 /n) of the photoresponsive azo-dye Disperse Red 1 (DR1) is analyzed within the constraints of the aforementioned model. The crystal bending kinetics depends on intrinsic factors (crystal size) and external factors (excitation time, direction, and intensity).