Bragg-case limited projection topography study of surface damage in diamond-crystal plates

Abstract

To characterize diamond monochromators for synchrotron radiation beamlines, images for a region 25 µm below the surface were obtained. Topographical images of a Bragg-diffracted beam having a scattering angle (twice the Bragg angle) of 90° were obtained from asymmetric reflections with a CCD area detector. A 25 µm incident slit was used to section the sample topographically. Patchwork images for the full surface area, but limited in depth to the slit size, were assembled from microbeam images. The small extinction depths provided by the asymmetric reflection geometry, namely, 2.8 µm and 3.5 µm for ideal diamond crystals set for the (224) and (044) reflections, respectively, permitted data analyses for a region near the surface. The diamonds were synthetic type Ib (yellowish due to nitrogen impurities). They were in the shape of plates sized 6 × 5 mm and were 0.5 mm thick. Measurements were made using monochromatic bending magnet radiation at the Advanced Photon Source at 12.04 keV and 13.90 keV. Data obtained before and after chemical etching demonstrate that damage visible as contrast from saw grooves is largely removed by etching. Dislocation etch pits were observed after etching for the (111) surface but not for the (100) surface.