HPHT Growth of High-Quality Diffraction Grade Diamond Substrates for X-Ray Optics

Next-generation of synchrotron and Free-Electron Laser X-ray sources will increase the peak power by several orders of magnitude. In these conditions, X-ray intensity will become too severe for the existing materials. Large, single-crystal diamond is one of the few materials, if not the only one, suitable for high-power X-ray optical applications due to its unique combination of high thermal conductivity, low thermal expansion, and low X-ray absorptivity. We developed the modified High-Pressure High-Temperature (HPHT) temperature gradient growth technology that allows for growing the highest crystalline quality large diamond crystals, with dislocation density of less than 10 cm^-2. This near-equilibrium process is carried out under extreme conditions, where diamond single crystals are grown from a molten metal solvent (Fe, Ni, and Co and their alloys) under pressures in excess of 5 GPa and temperatures of 1,600 K and higher. Since there are no available diagnostics to monitor crystal growth in the HPHT cell directly, both indirect experimental growth monitoring and faithful models are needed to connect experimental outcomes to system design and process conditions. We present initial results from a collaboration that includes experimental growth carried out at the Euclid Beamlabs and two modeling efforts by the University of Minnesota and Fraunhofer. X-ray white beam topography of grown crystals is also discussed. This two-fold approach provides rigorous tools to both understand growth in this system and to perform subsequent optimization of growth conditions. In particular, we aim to more fully understand fundamental aspects of diamond nucleation and growth and identify process conditions that will achieve the highest crystalline quality in large diamond crystals.