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Diamond exhibits large application potential in the field of power electronics, owing to its excellent and desirable electronic properties. However, the main obstacles to its development originate from the small‐sized single‐crystal wafers and the instability of the electrical conductivity. This work presents a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) on a diamond substrate derived from a five‐inch (110) highly preferred polycrystalline diamond film. The MOSFETs with excellent performance are fabricated by combining an H‐terminated channel and an epitaxially grown boron‐doped layer as the source/drain contacts of the diamond devices. According to the electrical statistical results of ≈110 devices on the polycrystalline diamond substrate, 44% of devices show normally‐off operation with a maximum current density of 400 mA mm−1, while 56% of devices demonstrate normally‐on operation with a maximum current density of 525 mA mm−1. The normally‐off characteristics are more related to the higher amounts of nitrogen concentration than the grain boundaries. The stable boron‐doped source and drain provide a high concentration of holes, which facilitate transport in the surface p‐type channel induced by the H‐termination. The characteristics of the MOSFETs are inspiring for the fabrication of complementary inverter circuits on large diamond wafers. [ABSTRACT FROM AUTHOR]

In this study, standard diamond bars were prepared using an ultra-thick diamond plate, and the bars had sizes consistent with the International Organization for Standardization (ISO) 14704:2016(E) three-point bending method for measuring the fracture strength. Ultra-thick diamond plate with dimensions of 125 mm (diameter) × 6.5 mm (thickness) were deposited using direct current arc plasma jet chemical vapour deposition. After cutting, grinding, and polishing, 12 diamond bars meeting the requirements of the ISO standard were prepared (36 mm × 4 mm × 3 mm) and tested for fracture strength using the cited ISO standard and elastic modulus using deflection measurements. The fracture strength of the ultra-thick diamond plate was found to be 580 ± 66 MPa. In addition, for comparison, the fracture strengths of standard ZnS, sapphire, and alumina were also analysed. Crucially, this is the first report of the fracture strength of standard-sized diamond plate. The effects of the defects and grain size on the crack formation and failure of the diamond film were analysed. The diamond's fracture strength was affected by the sample thickness, which caused the gradual accumulation of defects as this dimension increased, but not by its length and width. The elastic moduli of sapphire and alumina were compared. Overall, the measurement of the fracture strengths of ultra-thick diamond plate via the ISO standard is important for industrial applications. [ABSTRACT FROM AUTHOR]

The direct-current arc plasma jet method is advantageous for the rapid deposition of large-area self-supporting diamond films. However, dark defects tend to be generated during the growth process, significantly affecting the performance of the diamond. In this study, we use the direct-current arc plasma jet method to prepare transparent and translucent samples. Subsequently, we compare their optical, thermal, and mechanical properties and analyze the differences in their performances via microstructure and defect analyses. The results indicate that the transparent diamond samples exhibit excellent optical and thermal properties, with a transmittance of 68.4 % at a wavelength of 10.6 μm and a thermal conductivity similar to that of type-IIa single crystal diamond (i.e. 2002 W/(m·K)). Meanwhile, the translucent diamond exhibits outstanding mechanical properties, with a fracture strength of 984 MPa. Characterization results based on electron backscatter diffraction and X-ray computed tomography suggest that a preferred orientation along the (220) planes is conducive to the densification growth of the samples, thereby enhancing their optical and thermal properties. However, the generation of numerous twins results in interlocking between grains, which improves sample's mechanical properties but introduces porosity and impurities, thus deteriorating its optical and thermal performance. [Display omitted] • Optical and thermal diamond films were deposited by DC-arc plasma jet CVD with growth rates >6 μm/h. • Strong (220) texture and numerous twins can improve optical transmittance and fracture strength, respectively. • X-ray CT was used to reveal defects distribution and content within diamond samples. [ABSTRACT FROM AUTHOR]

Electronic and mechanical properties, and their biocompatibility, make diamond-based materials promising biomedical applications. The cost required to produce high quality single crystalline diamond films is still a hurdle to prevent them from commercial applications, but the emergence of polycrystalline diamond (PCD) films grown by chemical vapour deposition (CVD) method has provided an affordable strategy. PCD films grown on silicon wafer have been used throughout and were fully characterised by SEM, XPS, Raman spectroscopy and FTIR. The samples contain nearly pure carbon, with impurities originated from the CVD growth and the silicon etching process. Raman spectroscopy revealed it contained tetrahedral amorphous carbon with small tensile stress. The sp2 carbon content, comprised between 16.1 and 18.8%, is attributed to the diamond grain boundaries and iron-catalysed graphitisation. Antibacterial properties of PCD films were performed with two model bacteria, i.e. Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using direct contact and shaking flask methods. The samples showed strong bacteriostatic properties against S. aureus and E. coli with the direct contact method and no influence on planktonic bacterial growth. These results suggest that the bacteriostatic mechanism of PCD films is linked to their surface functional groups (carbon radicals and –NH 2 and –COOH groups) and that no diffusible molecules or components were involved. [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]

Polycrystalline CVD diamond films were subjected to transient heat treatment at the temperature range of 1500–1900 °C in the Ar/H 2 plasma arc environment. The structural changes of the diamond grain boundaries (GB) were indirectly investigated by employing IR optical absorption, Raman spectroscopy, X-ray diffraction (XRD), and fractographic scanning electron microscopy (SEM). The graphitization difference between near-nucleation side and near-growth side is mainly due to the difference in the GBs' content. It is proposed that the bonded‑hydrogen atoms, of which a large amount remained in the diamond GBs, play an active role in the process of graphitization. We recognized the intensity evolution of a peak in Raman spectra located at 1470 cm−1, which was attributed to the trans -polyacetylene at diamond GBs. This result suggests the likelihood that the long-chain hydrocarbon precursor is involved in a mechanism for the sp3-to-sp2 transformation. As the propagation of the graphitization from diamond GB to grain interior, sp2 carbon with compressed state forms in its place due to the limited space for expansion. The graphite along GBs affects the fracture mode of the diamond films, which causes partial GBs to tear, while transgranular fracture occurs instead of directly intergranular fracture. [Display omitted] • A transient heat treatment method was employed to effectively keep the GB graphitization at an early stage. • The Graphitization model demonstrated the long-chain hydrocarbon precursor was involved in the sp3-to-sp2 transformation. • The fracture of annealed diamond was completed between transgranular and intergranular crack propagation. [ABSTRACT FROM AUTHOR]