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Optical diamond materials are essential for infrared optical windows, microwave windows, and laser windows due to their exceptional properties. However, dark features inside the diamond are significant factors limiting optical properties, particularly at high deposition rates. This work focuses on adjusting crystallographic parameters to prepare (110) oriented optical-grade polycrystalline diamond films, aiming to mitigate dark features. Diamond films deposited via microwave plasma chemical vapor deposition (MPCVD) exhibit discernible quality stratification. Characterization analysis of diamond film samples with varying levels of black defects reveals a correlation: films with higher dark feature content tend to exhibit a preference for the (111) orientation, accompanied by a significant presence of penetration twins and interstitial voids. Conversely, transparent diamond films demonstrate a prominent (110) orientation, featuring numerous contact twins that alleviate competition from penetration twins and original grains during growth. Electron backscatter diffraction (EBSD) and scanning electron microscope (SEM) results reveal that transparent diamond films cultivated with a pronounced preference for the (110) orientation manifest consistent and seamless contact twins, leading to fewer dark features and improved optical transmittance. In contrast, (111) oriented diamond film exhibits numerous penetration twins, and holes form between them. Based on the analysis, 5-inch optical polycrystalline diamond films with (110) orientation were achieved successfully by suppressing dark features. [ABSTRACT FROM AUTHOR]

The demand of small-angle x-ray scattering (SAXS) windows for in-situ characterization of materials nano-structures in a heated vacuum environment has been increased dramatically. High-quality diamond prepared by chemical vapor deposition (CVD) has become the preferred window material due to its excellent optical and mechanical properties. However, impurities and defects in diamonds may lead to the strong X-ray scattering especially in the heating process, affecting the testing accuracy of the object. In this work, single-crystal diamond (SCD) and polycrystalline diamond (PCD) films with different quality were prepared, and their SAXS properties were investigated at room temperature and heating under vacuum. The results show that the scattering intensity of the undoped high-quality SCD is small and uniform, while that of the SCD window doped with a small amount of nitrogen increases, mainly due to the nitrogen atoms and vacancy clusters scattering. While for the PCDs, the grain boundaries and the dark features lead to strong scattering background. As the temperature rises from room temperature to 280 °C, although the phonon vibration of diamonds exhibits the obvious temperature dependence, the coherent scattering of diamonds with X-ray hardly changes, indicating no new scatterers with the changed gyration radius were generated in the heating process. SCD and PCD windows were successfully applied in an in-situ heating SAXS cell. [ABSTRACT FROM AUTHOR]

With its excellent properties such as high thermal conductivity, strong radiation resistance and high electron mobility, diamond has become one of the most suitable materials for radiation detectors. Detector-grade diamond requires low impurity content, low dislocation density and other defects. However, it is very difficult to keep low impurities and low dislocations simultaneously in the actual crystal growth process. In this study, microwave plasma chemical vapor deposition (MPCVD) method was used to grow diamond layer on two high-quality HPHT diamond substrates with the previously optimized process conditions. The nitrogen impurity content and structure of the HPHT substrate and growth layer were characterized and analyzed. The results show that, the content of nitrogen impurity on two HPHT substrates are 7. 1 x 10-6% and 4. 04 x 10-8%, respectively, whereas in their epitaxial diamond layers, the nitrogen impurity content are 2. 1 x 10-7% and 5 x 10-8%, respectively. The full width at half-maximum of the rocking curve shows that the dislocation density of the MPCVD growth layer is comparable to the HPHT substrate, though some dislocations were introduced into the MPCVD growth layer, which increases the stress. Overall, the dislocations in the HPHT substrate and epitaxial layer of single crystal diamond are in the same order of magnitude. The high-purity single crystal diamond prepared in this work may be used in nuclear radiation detection and semiconductor fields. [ABSTRACT FROM AUTHOR]

In order to realize the practical use of diamond as a semiconductor material, large-area single-crystal diamond wafers with uniform quality are required. Mosaic growth is an effective method to produce inch-grade single-crystal diamonds. However, the quality of the wafer is limited by the junction interface seriously, because cracking occurs easily due to the high internal stress. In this paper, the repetition growth method was adopted to grow mosaic splicing single-crystal diamond without polycrystalline diamond interface. The high-quality single crystal diamond slices were reduplicated by microwave plasma chemical vapor deposition (MPCVD). The substrates were obtained by cutting a piece of CVD diamond along a plane perpendicular to 〈001〉 (with a (100)-oriented surface). The evolution of the growth characteristics around the junction of the substrates at different stages was studied. The results show that the surface of the epitaxial layers gradually evolves from blurry terraces to a regular well-ordered step flow. When the substrates have the same deviation direction and the off-direction angles are within 3°, the junction of the substrates can connect smoothly. Raman mapping shows that there is a mixture of tensile stress and compressive stress near the junction. As the thickness of the epitaxial layer increases from 280 μm to 560 μm, the range of tensile stress near the joint area expands from 85 μm to 150 μm, the maximum tensile stress increases from 0.08 GPa to 0.16 GPa. In addition, the value of FWHM in the X-ray rocking curve is less than 2.80 cm−1 around the junction, which indicates good crystal quality. [Display omitted] • The evolution of growth characteristics around the junction in the mosaic diamond was studied. • The mosaic boundary evolved from blurry terraces to a well-ordered step flow and finally connected. • The lowest value of tensile stress near the joint area was reported as the film thickness increased. • The larger FWHM of Raman peak around the junction is caused by the increased tensile stress. • The "inherit" effect of NV content of the epitaxial layer was observed for the corresponding substrate. [ABSTRACT FROM AUTHOR]