Abstract
Wavefront-preserving X-ray diamond crystal optics are essential for numerous applications in X-ray science. Perfect crystals with flat Bragg planes are a prerequisite for wavefront preservation in Bragg diffraction. However, this condition is difficult to realize in practice because of inevitable crystal imperfections. Here, X-ray rocking curve imaging is used to study the smallest achievable Bragg-plane slope errors in the best presently available synthetic diamond crystals and how they compare with those of perfect silicon crystals. It is shown that the smallest specific slope errors in the best diamond crystals are about 0.08 (3) µrad mm-2. These errors are only 50% larger than the 0.05 (2) µrad mm-2 specific slope errors measured in perfect silicon crystals. High-temperature annealing at 1450°C of almost flawless diamond crystals reduces the slope errors very close to those of silicon. Further investigations are in progress to establish the wavefront-preservation properties of these crystals.
Highlights
Diamond features a unique combination of outstanding physical properties perfect for numerous X-ray crystal optics applications where traditional materials such as silicon fail to perform
Perfect crystals with flat Bragg planes are a prerequisite for wavefront preservation in Bragg diffraction
The numbers in brackets represent the last-digit variation range for the provided numbers over 16 selected 1 mm  1 mm crystal regions of interest (ROIs). They show that the and ÆÁ values in particular ROIs of diamond can approach those measured in the reference silicon crystal
Summary
Diamond features a unique combination of outstanding physical properties perfect for numerous X-ray crystal optics applications where traditional materials such as silicon fail to perform. In the studies presented here, Bragg-plane slope errors are measured using X-ray Bragg diffraction rocking curve imaging (RCI), known as sequential topography (Lubbert et al, 2000). This technique is applied to best-available diamond crystals featuring relatively large areas ($4 mm  4 mm) almost free of dislocations, stacking faults, inclusions and other defects detectable by white-beam X-ray topography (Tuomi et al, 1974; Bowen & Tanner, 1998; Tran Thi et al, 2017), which is used to prescreen the diamond crystals. The Bragg-plane slope errors in diamond crystals are compared with those in the highest quality reference silicon crystals.
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