HPHT System for Near Dislocation Free Diamond Elements 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. Diamond is the most promising, if not only candidate, due to its high thermal conductivity, small thermal expansion, and low X-ray absorption. Unfortunately, the availability of large size, high-crystallinity, and low-defect density diamond substrates is very limited. Presently, there are no suppliers of high-quality diamonds with low defect concentrations in the United States to support this rapidly developing field of diamond X-ray optics applications for the next generation sources. We will develop the modified High-Pressure High-Temperature (HPHT) temperature gradient growth technology that will allow growing the highest crystalline quality large diamond crystals, with dislocation density less than 10 cm-2. Among two synthetic diamond lab-grown technologies, the HPHT approach is superior over CVD for X-ray applications due to its near-equilibrium growth nature that allows for large crystals with almost three orders of magnitude fewer defect densities than CVD-grown plates. The main prerequisite for the near dislocation-free HPHT diamond growth is a reduction of nitrogen impurities to less than 1 ppm-level. Unique total environmental control of all processing steps will be utilized to achieve required diamond crystal purity and structure perfection. In Phase I, an extensive process of modeling and optimization of TGG HPHT reactor geometry and growth parameters was conducted. We modeled temperature field distribution inside the HP chamber at different stages of diamond crystal growth. We identify conditions of cell geometry and ambient parameters necessary for increasing the crystal size. Despite COVID-19 obstacles, we were able to conduct two testing runs of HPHT crystal growth, optimized for reduced nitrogen contamination. In tight collaboration with the APS ANL team, the materials were characterized using several X-ray techniques. In addition, we performed optical cross-polarizer analysis, UV-light, and micro- Raman characterization of selected samples. We achieved very encouraging results: the grown crystals had already surpassed the sizes specified in the topic. The largest diamond plate cut from these crystals has dimensions 6.5x6.5x0.5 mm3. White-beam x-ray topography demonstrated near dislocation free quality, and analysis of spatial variations in the Bragg angle from the ideal direction was within 300 nrad/mm2 for the best sample. In Phase II, we will address the remaining HP cell design and technological questions and build a custom HPHT diamond reactor system. Multiple optimization trials will be performed to identify the best growth conditions for large size high-quality diamonds. X-ray and other characterizations will be conducted and analyzed after each test. At the end of Phase II, we will be well prepared to scale up and commercialize high-quality diamond substrates for scientific applications. This project's long-term goal is to establish the first USA-based HPHT diamond growth facility capable of producing the highest quality large SC diamonds matching X-ray optics requirements. The technology developed here is required to utilize X-ray beams at fourth generation light sources to maximum potential. High-quality diamond is virtually the only material that can withstand the next- generation light sources' heat load. If a manufacturing technology for large size HPHT diamond substrate is established, diamond-based optical elements will supersede the current silicon and beryllium alternatives, which have lower performance and severe health and safety concerns. High-quality diamond material will also benefit quantum computing, industrial, medical, and other industrial applications.