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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]

Ultra-nanocrystalline diamond (UNCD) films exhibit excellent mechanical properties because of their unique structure, such as small grain size and high grain boundary ratio. The effect of nitrogen atoms in nitrogen-doped UNCD films on their structure and mechanical properties deserves in-depth study. In this study, we focus on the microstructure control of UNCD films and its effect on the mechanical properties. Ultra-nanocrystalline diamond films were prepared using microwave plasma chemical vapor deposition under varying nitrogen flow rates. It was observed that the hardness and elastic modulus of UNCD films initially increased and then decreased with the increase of nitrogen flow rate. The structure of UNCD films was characterized using transmission electron microscopy and the crystal quality was analyzed through Raman spectroscopy. Nitrogen-interstitial atom defects were identified in the photoluminescence spectra. These defects contribute to shorter interatomic bonds and enhance the covalent bonds in the crystalline structure, resulting in an increase in hardness. The sp2/sp3 ratio and effective nitrogen atom concentration in the UNCD film were analyzed by X-ray photoelectron spectroscopy. The results indicate that an increase in the effective nitrogen atom concentration corresponds with a notable reduction in grain size, which is simultaneously accompanied by a rise in the number of grain boundaries. Meanwhile, the increase of sp2 content in the UNCD leads to the increase of grain boundary width and density, resulting in the increase of hardness and elastic modulus. This work provides theoretical basis and experimental guidance for the development of high performance UNCD films through precisely regulating the microstructure. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is critical in water splitting for green hydrogen gas production due to its sluggish kinetics; however, commercial OER catalysts commonly suffer from high cost, low catalytic activity and poor stability. Herein, we developed a C+ ion implantation method to modify single crystal diamond, and the resultant surface amorphous layer not only raised the active site number but also increased the content of the C=O group, thus significantly improving the OER activity. The C+ ion implanted high-temperature and high-pressure (C+-HTHP) and chemical vapor deposition (C+-CVD) diamonds both exhibit low OER overpotential with η 10 of 317 mV and 325 mV respectively, superior to those of HTHP diamond (360 mV), CVD diamond (395 mV) and RuO 2 (364 mV). The potentiostatic testing shows that the C+ implanted diamonds almost didn't undergo the rise of OER overpotential upon catalysis for more than 12 h at a current density of 10 mA cm−2, suggesting a high catalytic stability, owing to the strong bonding between single crystal diamond and amorphous carbon layer. For the first time, we utilized carbon ion implantation to prepare diamond-based high-performance OER catalyst, which broadens the understanding of carbon-based materials in OER catalysis. [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]

Lift-off is a promising method to prepare thin, high-finish, and freestanding large-area single crystal and polycrystalline diamonds. However, accurate control of the damage layer characteristic to achieve both stress release and lift-off process is difficult. In this work, high-energy C+ was implanted in single crystal diamond and polycrystalline diamond to create subsurface damage. The defect behavior and structural transformation of the ion implantation and annealing process were investigated. The homoepitaxial growth was subsequently carried out and the epitaxial layer was lifted off from the substrate by selectively etching the damaged layer. The results show that the cap layer and the substrate (below the damage layer) keep the sp3 carbon structure before and after annealing, which is confirmed by the atomic-scale electron energy loss spectroscopy (EELS). The high-resolution transmission electron microscopy (HRTEM) images show that after annealing at 1000 °C for 1 h, the damaged layer was transformed from amorphous carbon to a mixture of graphite and amorphous carbon, providing the damaged layer that could be removed by electrochemical solution. Meanwhile, the distorted diamond area was changed to a sharp interface, which ensures the low roughness of the substrate surface after the lift-off process. After etching for 30 h, a freestanding polycrystalline diamond film with a thickness of 100 μm and a surface roughness of 1.68 nm was obtained. The roughness of the lift-off substrate surface is 1.10 nm, indicating the epitaxial growth can be repeated directly without polishing. [Display omitted] • The defect behavior and structural transformation of the high-energy C+ implanted diamonds were investigated. • The stress state of the diamonds before and after ion implantation and after lift-off process were evaluated. • A 100 μm-thick freestanding polycrystalline diamond film with a surface roughness of 1.68 nm was successful obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high channel hole mobility of 200 cm2V−1s−1 was achieved in C-Si interface (1 1 1) diamond MOSFETs. • The C-Si interface provides the MOSFETs with an excellent normally-off operation. • The advantage of boron doping in (1 1 1) diamond provides a large maximum current density. • The anatomically flat and strain-free interface between the (1 1 1) diamond and SiO 2 film was confirmed by HRTEM. • The existence of C-Si bonds at the interface was proved by EELS and XPS. In this paper, a diamond-silicon (C-Si) interface was constructed on a (1 1 1) diamond substrate by annealing the SiO 2 gate insulator in a reductive atmosphere. Corresponding metal-oxide-semiconductor field effect transistors (MOSFETs) with a C-Si conductive channel were fabricated. The MOSFETs demonstrate excellent normally-off operation with a high threshold voltage (V th) of −16 V and a high current density of −167 mA/mm, with a gate length (L G) of 4 μm. The channel hole mobility (μ FE) reaches 200 cm2V−1s−1 with a L G of 10 μm, and the interface state density (D it) is as low as 3.8 × 1011 cm−2 eV−1. The high-resolution transmission electron microscopy (HRTEM) image displays a coherent and strain-free interface between the SiO 2 film and (1 1 1) diamond, which ensures a high μ FE and low D it in the MOSFETs. The interface is dominated by C-Si bonds, which are confirmed by atomic-scale electron energy loss (EELS) quantification, spectroscopic characterization, and X-ray photoelectron spectroscopy (XPS). These results demonstrate that diamond, directly combined with SiO 2 , is ideal for implementation in power devices. [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]

The surface conductivity on the H-terminated diamond is still an interesting topic in the field of diamond electronics. Until now, the carrier mobility in the conductive channel has been limited to below 200cm2/Vs due to the various surface scattering mechanisms. In this paper, a high mobility conductive channel on the H-terminated diamond surface was reported. Firstly, the high quality diamond films were deposited on the commercial CVD diamond substrates. After polishing, the H-termination was obtained by hydrogen plasma treatment. The surface morphology of the H-terminated diamond was observed by atomic force microscope (AFM) and scanning electron microscope (SEM). The crystal quality on the diamond surface was characterized by Raman spectroscopy. The impurities in the crystals were tested by photoluminescence spectroscopy. The surface conductivity of H-terminated diamond was monitored comprehensively by Hall test. It can be found that the sheet resistance decreases much and the carrier mobility increases dramatically after the hydrogen plasma treatment and mechanical cleaning. The maximum mobility value is up to 365cm2/Vs with carrier density of 2.9 × 1012 cm−2, which is the highest value reported. Raman spectra of diamond surface show that a peak appears at 1121.4 cm−2 after the hydrogen plasma treatment, which corresponds to the nanocrystal diamond or carbon clusters of sp3 bonded material. The corresponding mobility enhancement mechanism on the H-terminated diamond surface was proposed. Unlabelled Image • The carrier mobility enhancement on the H-terminated diamond surface was found. • A thin carbon film on the diamond surface was observed with Raman peak at 1121 cm−1. • The H-terminated diamond surface showed high carrier mobility of 365cm2/Vs. • The corresponding mobility enhancement mechanism was proposed. [ABSTRACT FROM AUTHOR]