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Y 2 O 3 anti-reflection films were deposited on freestanding chemical vapor deposited (CVD) diamond substrates by radio frequency magnetron sputtering. The effects of oxygen–argon ratio on microstructure, composition, optical property and mechanical property were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transformed infrared spectroscopy, and nanoindentation. The results showed that the crystal structure of Y 2 O 3 films transformed from cubic to monoclinic with the increase of oxygen–argon ratio. Meanwhile, the degree of non-stoichiometry of the film with the monoclinic phase was higher than the film with the cubic phase. Both monoclinic and cubic Y 2 O 3 film had an anti-reflection effect on diamond in the 8–12 μm long-wavelength infrared (LWIR) range. However, the maximum transmittance of the Y 2 O 3 film-coated diamond was shifted to lower wavelengths, which were mainly attributed to the reflective indexes of the Y 2 O 3 film that decreased with the increase of the oxygen–argon ratio. The Y 2 O 3 film with a cubic phase had high resistance to abrasion and plastic deformation. Therefore, the Y 2 O 3 film with a cubic phase was much more suitable for long-wave infrared application. [ABSTRACT FROM AUTHOR]

Abstract: Highly c-axis oriented ZnO film is often deposited on diamond substrates by RF magnetron sputtering and widely used for high frequency surface acoustic wave (SAW) devices. Deposition temperature is a key factor affecting the quality of the ZnO film. Different quality polished free-standing diamond films prepared by DC Arc Plasma Jet were used as the substrates to deposit ZnO films at different temperatures. Effect of the deposition temperature and the quality of the diamond films on the properties of the ZnO films were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that highly c-axis oriented ZnO films can be much easier deposited on the optical-grade diamond films with <111> preferred orientation than the tool-grade diamond films with <220> preferred orientation. The optimal deposition temperature is 200°C for highly c-axis oriented and lower roughness ZnO films. Acoustic phase velocity of more than 10,000m/s for the SAW devices based on the ZnO/optical-grade free-standing diamond films was obtained. [Copyright &y& Elsevier]

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]

Abstract: A destroyable Ti interlayer on graphite substrate was used for fabrication of crack-free free-standing diamond films by high-power DC Arc Plasma Jet. Ti interlayer was arc ion plated on the polycrystalline graphite substrate. The thickness, morphology and composite phase of the Ti interlayer were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Titanium carbide (TiC) was detected in both sides of the interlayer, which played an important role with respect to reasonable adhesion and diamond nucleation. Semi-translucent and crack-free diamond films were obtained and characterized by SEM and Raman spectroscopy. It is shown that the diamond films so obtained have excellent Raman signature. The overall results suggest that plating Ti interlayer on graphite substrate is an effective way to obtain potentially crack-free free-standing diamond films. [Copyright &y& Elsevier]

Diamond radiation detector is an ideal choice for the next-generation radiation detection in harsh environments, due to its small size, high irradiation resistance and fast response. However, high-purity single crystal diamond is hard to be prepared at the high growth rate due to the inevitable impurity incorporation. In this paper, based on the high-quality high-temperature/high-pressure (HPHT) single crystal diamond substrate, detector-grade single crystal diamonds material with high purity and low defect density were epitaxially grown at growth rate of about 4 μm/h by using plasma environment purification technology. It showed that the full width at half maximum of X-ray rocking curve of high-quality single crystal diamond could reach 0.007°, there was no nitrogen related impurity in PL spectrum, and the substitutional nitrogen content estimated by UV absorption spectrum was less than 10 ppb. After metallization and packaging process, the diamond detectors were prepared and the detector response under irradiation with 241Am α-particles was realized. For the sample with fewer dislocations, the charge collection efficiency and energy resolution of this detector were 86.8 % and 7.85 % for electrons, and 96.7 % and 2.48 % for holes. The product of mobility and lifetime of electrons and holes were 1.7 × 10−4 cm2V−1 and 3.7 × 10−4 cm2V−1, respectively. The high performances of the detector indicate that the current diamond detector can meet the application requirements of commercial diamond detectors. [Display omitted] • Detector-grade diamond was prepared by plasma environment purification technology. • The high-purity single crystal diamond was grown at growth rate of about 4 μm/h. • The diamond detector with charge collection efficiency of 96.7 % was realized. • The products of mobility and lifetime of electrons and holes were 1.7 × 10−4 and 3.7 × 10−4 cm2V−1. [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]

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]

In-situ micro-area analysis of precisely polished polycrystalline diamond (PCD) film by high-speed three-dimensional dynamic friction polishing (3DM-DFP) is carried out in this work, continuing from the previous works focusing on the subsurface cleavage and polishing mechanism. Multi-orientational grains with variable hardness anisotropy are generally considered the reason for the surface irregularity of PCD after smoothing. The unreached surface ultra-smoothness in local region after polishing is mainly resulted from the height difference at grain boundary (GB) area (e.g. , a selected GB micro-region is of around Ra roughness of 5.7 nm and altitude intercept of 6.6 nm). However, different individual grains nearby showing (100), (110), (111) orientations are all of roughness <0.5 nm, demonstrating these places are contiguously polished. The observed local roughening at GBs region after mechanical sliding accompanying with friction heat is the major factor to cause the surface irregularity, which is affected by the inhomogeneity of crystal thermal expansion and contraction associated with the defects in multi-orientational crystals generated by mechanical process. Among multi-crystals the low-position (110) region has a Ra roughness of 0.1 nm but with great tensile stress and relatively weak distortion compared with other orientational areas. An insight of the inhomogeneous volume change associated with thermal expansion and contraction affected by defects condition was proposed to straightforwardly illuminate the rationale of GB effects on the ultra-smoothing of PCD by 3DM-DFP. [Display omitted] • A phenomenon deteriorating ultra-smoothing of PCD by high-speed 3DM-DFP was found. • In-situ micro-area analysis of PCD before and after 3DM-DFP was carried out. • The height difference at GBs is resulted from the CTE inhomogeneity associated with defects. [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]

To unfold the promise of diamond as an advanced technical material, single-crystal diamonds (SCDs) and polycrystalline diamonds (PCDs) were smoothed by high-precision three-dimensional movement dynamic friction polishing (3DM-DFP) to achieve the ultra-smooth surface with roughness <5 nm (even 1 nm) more effectively. However, this inevitably leads to subsurface damage growth, i.e., subsurface defects evolved from nearly damage free to partial defects, and to cleavage faults beneath the SCD surface, resulting from mechanical fatigue and/or the rate of energy input by increasing the linear polishing velocity (from 12 m s−1 to 60 m s−1). In this study it was elucidated, for the first time, the subsurface uniform tile-roof-like cleavage faults and its formation mechanism of diamond after 3DM-DFP at the superhigh speed of linear sliding velocity of 60 m s−1. And the generated subsurface damage would be extended to about 10 μm in depth of the (100) SCD and manifested as micro-cleavage fault region, transition area and compressive zone. Meanwhile, two Raman peaks of 1425 cm−1 (first-order) and 2200 cm−1 (second-order) are assigned to the subsurface damage, which is the amorphous carbon (quasi sp 3 + sp 2) resulting from the cleavage along (111) crystal planes, based on the fine analysis of Raman spectroscopy and the study of subsurface defect evolution in different types of diamonds. Moreover, the assignment of concomitant peaks of 1750 cm−1 (localized defects) and 2100 cm−1 (sp 1 chains) were revealed. Unlabelled Image • SCDs and PCDs with roughness <5 nm (even 1 nm) were smoothed by 3DM-DFP. • Uniform subsurface cleavage was generated in SCD after 3DM-DFP at linear velocity of 60 m s−1. • Mechanical damage beneath the SCD (100) surface would be extended to 10 μm in depth. • Heavy subsurface damage comprises cleavage, transition and compressive regions. • Subsurface a -C consisting of quasi sp 3 + sp 2, sp 1 and C V was revealed after 3DM-DFP. [ABSTRACT FROM AUTHOR]