A natural diamond plate of thickness 0.55 mm, polished parallel to (110), contained a dislocation-free and unusually distortion-free area into which a beam of fluorine ions of 17 MeV energy had been injected. The beam, the diameter of which was pinhole-limited to ∼3/4 mm, produced a radiation-damaged layer at ∼5 µm depth and uplifted the crystal above to form an optically detectable mesa. Conventional X-ray topography registered lattice distortion strongly at the mesa periphery, but did not disclose the deformation of near-surface lattice layers at the mesa centre. In contrast, reticulography showed directly that the central surface lattice layers were slightly domed outwards. (In reticulography, a fine-scale X-ray absorbing mesh placed between a Laue-reflecting crystal and the topograph-recording plate splits the diffracted beam into individually trackable microbeams, the direction differences of which are measured by recording them at different mesh-to-plate distances.) Reticulographs were recorded in back-reflection, 2θB= 135°, using both symmetric reflection from the (110) surface, reflection 440 dominant, with λ = 0.116 nm, and reflection 331¯, with λ = 0.151 nm. The metrological procedures and geometrical analysis applied are described. The central surface curvature was derived from ten reticulographs recorded under different conditions, which tested the reproducibility of the method. Deviations of individual radius values from the mean were ∼4% for both curvature in (001) and orthogonally in (1¯10), the overall mean being 5 m. Two-beam optical interferometry failed to measure this curvature.
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