X-ray reflectivity of chemically vapor-deposited diamond single crystals in the Laue geometry

Abstract

The absolute X-ray reflectivity of chemically vapor-deposited (CVD) single-crystal diamond plates was measured in the Laue geometry in the double-crystal non-dispersive setting with an asymmetric Si beam-conditioner crystal. The measurements were supplemented by rocking-curve topography. The measured reflectivity curves are examined in the framework of the Darwin-Hamilton approach using a set of two independent parameters: the characteristic thickness of mosaic blocks and their average angular misorientation. Owing to strong extinction effects, the width of the reflectivity curves does not directly represent the average misorientation of the blocks. Two different sets of parameters were found for the 111 asymmetric reflection in the two different scattering configurations (beam compression and beam expansion). Analysis of the rocking-curve topographs shows that this discrepancy can be attributed to inhomogeneity of the diamond crystal microstructure.

Side-bounce beamlines using single-reflection diamond monochromators at Cornell High Energy Synchrotron Source

“…The dislocation density was greater than what conventional X-ray topography techniques can resolve (Bowen & Tanner, 1998), as confirmed in our prior study (Stoupin et al, 2019a), which included white-beam Laue X-ray topography. This resulted in an increase in the reflection intensities due to the enhancement of the effective intrinsic energy bandwidth (Stoupin et al, 2018(Stoupin et al, , 2019b. The CVD plates were of two distinct crystallographic orientations: plates of the first type had a nominal 110 Rocking-curve topographs for the large diamond plate, which was chosen as the 111 Bragg reflector in the high-heat-load monochromator of beamline 3B.…”

“…As a result, the size of the beam profile inevitably increases in both dimensions. At the same time, the integrated reflectivity of the CVD crystal can be greater by an order of magnitude or more (Stoupin et al, 2018). For those experiments which do not require the high energy resolution provided by perfect crystals (ÁE/E ' 10 À4 ), an increase in the total available size of the beam can be considered an advantage provided that the flux per unit area (flux density) is not reduced.…”

Selection of CVD Diamond Crystals for X-ray Monochromator Applications Using X-ray Diffraction Imaging

“…The benefits are a relatively low cost of the element and a reduction in the monochromator operational expenses (possible use of water cooling as opposed to cryogenic cooling under conditions of high incident X-ray power density). In the previous study we described substantial broadening of X-ray rocking curves in sc-CVD diamond plates while retaining high reflectivity in the Laue geometry for hard X-rays [9]. The challenge for the application of sc-CVD diamond crystals as X-ray monochromator elements at synchrotrons originates from distortion of the radiation wavefront of the reflected X-rays due to imperfections of the crystal lattice.…”