Study of the elastically deformed state of thin diamond plates

The development of laboratory technologies for growing high-quality diamond single crystals, as well as low thermal expansion of a diamond, make it possible to consider this material promising as an element of X-ray optics in designing free electron lasers (XFEL). Diamond crystal-spectrometers of various thicknesses and bending radii are also in demand. In this regard, the issues regarding the mechanical parameters of elastically deformed diamond single crystals require clarification, among them critical stresses in a deformed single crystal and the minimum bending radii for plates of certain geometry. The goal of the study is determination of the elastically deformed state of thin diamond plates with the parameters required in spectrometers for non-invasive diagnostics of X-ray free-electron laser (XFEL) spectra. The samples were cut from the IIa -type crystal of the highest quality grown by the temperature gradient method. Diamond plates with (110) and (111) crystallographic orientations were used in the experiments. The dependences of the stresses and bending radii on deformation value were obtained during bending thin diamond plates with a thickness of 20 μm. The experimental deformations did not exceed 1 mm. The minimum bending radii of thin diamond plates were also determined: for (111) direction — 5.6 mm, and for (110) direction — 4.5 mm. The Young’s moduli were 1198 GPa for (111) direction and 1034 GPa for (110) direction. Critical stresses during bending of thin diamond single crystals (resulting in their destruction) exceeded 2.4 GPa. The dependence of the bending radii of crystals on their thickness was calculated at a stress value of 2.0 GPa. The results of the study make it possible to calculate the allowable deformations for thin diamond plates of arbitrary shape and thickness. The data obtained will contribute to the improvement of modeling and the quality of production of curved spectrometers.

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