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  • Abstract：In this study, a single-crystal diamond (SCD) MEMS cantilever was fabricated using a buried graphite sacrificial-layer process. A region containing nitrogen-vacancy (NV) centers formed near the ion-implantation-induced defective layer was directly utilized as the stress-sensing region of the released cantilever, enabling dynamic stress sensing without the use of externally attached nanodiamonds. We investigated the relationship between the stress induced by the cantilever vibration and the peak shift of the fluorescence intensity of the optically detected magnetic resonance (ODMR) spectrum. By approximately aligning the static magnetic field with one of the four NV-center crystallographic axes, we were able to evaluate the dependence of the peak shift on stress. Our findings revealed that the peak shift can effectively detect uniaxial stress due to normal vibration. In addition, as the vibration amplitude increased, the magnitude of the ODMR peak shift also increased, showing a trend consistent with previously reported NV-center stress responses. Furthermore, the ODMR shift exhibited periodic modulation corresponding to the cantilever’s vibration phase. These results indicate that NV centers in micromachined SCD cantilevers can be used to detect vibration-induced dynamic bending stress.  

    Yuta Ochiai, Vu Xuan Tung Duong, Zilong Zhang, Takahito Ono, Meiyong Liao, Masaya Toda

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  • Abstract：Diamond surfaces terminated with a silicon layer (C–Si) can induce a two-dimensional hole gas (2DHG) layer at the insulator/diamond interface, enabling the realization of p-channel metal–oxide-semiconductor field-effect transistors (MOSFETs). Through two primary fabrication routes—namely, SiO2 annealing in a reducing atmosphere and silicon molecular beam deposition (MBD) at high temperatures—stable oxidized silicon-terminated (C–Si–O) and C–Si diamond channels have been realized. These channels facilitate normally-off p-channel FETs with threshold voltages (VTH) ranging from −3 to −16 V and hole mobilities between 100 and 200 cm2/V·s. For instance, a (111)-oriented C–Si–O MOSFET with a VTH of −5.6 V delivers an output current density of −311 mA/mm, whereas another MBD C–Si–O MOSFET with a varying source-to-drain distance (LSD) shows a ΔVTH shift whose magnitude is less than 0.2 V. This review provides a critical overview of the chemical structures, the formation methods, and operational mechanisms of C–Si–O diamond surfaces. It also summarizes recent progress in C–Si–O diamond electronic devices, with emphasis on device architectures, fabrication techniques, and electrical characteristics. Finally, key challenges and potential pathways toward the industrial adoption of this emerging technology are discussed.  

    Yu Fu, Ze Peng, Jinfeng Zhang, Zeyang Ren, Kai Su, Hiroshi Kawarada, Yue Hao, Jincheng Zhang

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  • Abstract：Diamond possesses excellent physical and electronic properties, and demonstrates great application potential in the next-generation high-power and high-frequency power electronic devices. In recent years, significant progress has been made in the research on diamond diodes and field-effect transistors (FETs). This paper summarizes the effects of channel types, gate dielectrics, substrate types and device structures on the performance of diamond FETs and diodes. The hydrogen-terminated surface provides a high-performance channel for FETs through the formation of a two-dimensional hole gas, while Al2O3 and h-BN and other gate dielectric materials play a key role in reducing interface state density and improving the high-temperature stability of the devices. The development of high-quality 2-inch sapphire heteroepitaxial diamond substrates effectively alleviated the problem of size limitations of diamond substrates, providing a feasible solution for the fabrication of large-area and low-cost diamond devices. The article analyzes the factors that affect the core performance of diamond devices, including breakdown voltage, on-resistance, current density and threshold voltage. The field plate structure can alleviate the edge electric field concentration effect of the Schottky metal, effectively increase the breakdown voltage of the diamond Schottky diode, and does not sacrifice its forward characteristics. We discuss the main bottlenecks and challenges that currently restrict the development of diamond devices. We propose effective strategies to enhance the overall performance of diamond electronic devices from perspectives such as material growth, interface engineering, and structural design. This article aims to provide scientific references for the design and development of high-performance diamond electronic devices.  

    Cheng Wang, Chuang Wang, Gengyou Zhao, Bo Feng, Liangxue Gu, Kun Tang, Shunming Zhu, Jiandong Ye, Shulin Gu

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  • Abstract：Polycrystalline diamond films and coatings are widely used in optical components, thermal management, and cutting tools. Chemical vapor deposition (CVD) is widely used for their synthesis, while the initial nucleation stage largely determines the continuity and morphology of the diamond layer. Conventional nucleation is achieved by surface seeding with nanodiamond particles. An alternative approach is chemical nucleation, extensively studied for carbon-containing precursors and polymers, whereas nucleation on non-carbon particles remains comparatively unexplored. Here, lithium fluoride (LiF) particles were used as a model non-carbon system to study diamond nucleation and subsequent growth in CH4–H2 microwave plasma CVD. Surface morphology and Raman spectroscopy showed that LiF promotes localized formation of well-faceted diamond crystallites without conventional nanodiamond seeding. Increasing the substrate temperature to 900°C produced a nearly linear increase in nucleation density and enabled the formation of nearly continuous polycrystalline films, whereas further heating to 950°C promoted island-like growth despite increasing growth rate. Methane concentration mainly affected the growth regime: at CH4 contents of 10% and higher, secondary nucleation became pronounced, suppressing crystallite enlargement and promoting the transition from microcrystalline to nanocrystalline diamond. Raman analysis showed that substrate temperature had little effect on the sp3/sp2 ratio, although the diamond Raman line broadened at higher temperatures, whereas elevated methane concentrations increased the contribution of non-diamond carbon phases. These findings suggest that non-carbon chemical nucleation can provide a new perspective on diamond formation during CVD, including the emergence of diamond nuclei under conditions where diamond remains thermodynamically metastable.  

    Ivan A. Tiazhelov, Artem K. Martyanov, Sergey V. Kuznetsov, Sergey S. Savin, Alexander A. Zhivopistsev, Victor G. Ralchenko, Vitaly I. Konov, Vadim S. Sedov

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  • Abstract：Boron and nitrogen co-doped diamond (BNDD) has attracted extensive research attention owing to its promising potential for n-type conductivity. However, boron–nitrogen (B–N)-related complexes in BNDD lead to highly complex optoelectronic properties, which hinders its practical applications. In this study, we present a systematic investigation of the electrical and optical properties of BNDDs with graded nitrogen doping, both in the as-grown state and after high-pressure high-temperature (HPHT) annealing. Nitrogen incorporation is found to sharply increase the resistivity of boron-doped diamond, dominated by enhanced hole scattering from nitrogen-associated defects and impurities. Following HPHT annealing, all BNDDs maintain stable p-type conduction with an elevated hole concentration, which benefits from the combined effects of neutral boron acceptor activation and intrinsic B–N complex dissociation. Strikingly, donor–acceptor pair (DAP) recombination luminescence appears concurrently with a drop in hole concentration in high-nitrogen BNDDs annealed above 2000 °C, directly confirming neutral nitrogen donor activation under HPHT conditions. This work provides a practical strategy for the performance modulation and optimization of BNDD, and reveals the activation effect of HPHT annealing on nitrogen impurities, providing a feasible path toward the realization of n-type diamond.  

    Liangxue Gu, Jiaqi Xia, Shuang Ye, Chuang Wang, Shulong Zhang, Zhonghao Ye, Man Ye, Chengchun Zhao, Yin Hang, Shulin Gu

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  • Abstract：Homoepitaxial single-crystal diamond grown by MPCVD is increasingly recognised as the optimal substrate for NV centre-based quantum sensors. Establishing eligibility for quantum applications requires evaluating four properties that exceed standard semiconductor criteria: crystal orientation, bulk crystallinity, epilayer–substrate misalignment, and surface roughness. X-ray techniques are uniquely suited to this task, being non-destructive, quantitative, requiring minimal preparation, and spanning laboratory and synchrotron facilities bridging wafer-scale screening and device-region certification. This review critically surveys X-ray methods addressing all four properties: high-resolution X-ray diffraction (HRXRD) rocking curve analysis, synchrotron and laboratory topography, reciprocal space mapping (RSM), X-ray reflectometry (XRR), grazing incidence diffraction (GIXRD), pole figure analysis, and Bragg diffraction imaging. Reported HRXRD (004) rocking curve FWHM values reach 0.0027° (9.7 arcsec) for the best CVD films, approaching the theoretical Darwin width. Synchrotron topography enables Burgers vector identification and dislocation density mapping below 10⁵ cm–²; RSM separates lattice tilt from strain; XRR resolves the sub-nanometre roughness required for shallow NV implantation. We examine how MPCVD growth parameters like substrate misorientation, nitrogen addition, temperature, and methane concentration imprint on X-ray signatures, and establish quality thresholds linking X-ray metrics to NV coherence (T₂ up to 2.4 ms in ¹²C-enriched, phosphorus-doped n-type CVD diamond), distinguishing T₂ from T₂*. Critically, X-ray observables are necessary-but-not-sufficient structural proxies: they certify the host lattice, while spin-bath-limited T₂, zero-phonon-line homogeneity, charge-state stability, and charge-collection efficiency require EPR, SIMS/FTIR, photoluminescence, ODMR, and device-level metrology. We present a “ready reckoner” cross-mapping each X-ray observable to the metrics it can and cannot predict and recommend a standardised HRXRD/XRT–RCI/RSM/XRR protocol with defined pass/fail thresholds for community-wide quantum-grade qualification.  

    Luke Chia Wei Min, Siu Hon Tsang, Apoorva Chaturvedi, Edwin Hang Tong Teo

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  • Abstract：lumina (Al2O3) ceramics with complex geometry are widely used in aerospace thermal components, cutting tools, and catalyst supports because of their excellent thermal stability, corrosion resistance, and wear resistance. However, low ductility problem existed in such brittle material and influences its long-term stable service in extreme environments, especially under load-bearing conditions. Adding carbon material were considered as an effective method to improve mechanical properties of ceramics. In this work, diamond/Al2O3 composites were fabricated using digital light processing (DLP) additive manufacturing technology. Meanwhile, their microstructure, phase composition, and compressive properties were systematically investigated here. After sintering treatment, Al2O3 particles retained a well-defined morphology and unchanged phase composition, which had an average particle size of 6 μm. Diamond particles had an average particle size of 1 μm and transformed obviously from a crystalline structure to an amorphous state, accompanied by characteristic graphitization peaks. From mechanical properties testing results of DLP composites, the specimens exhibited elastic modulus of 331.23 ± 8.69 MPa and compressive strength of 46.19 ± 1.07 MPa. Specially, diamond/Al2O3 composites specimens had an increasing in elongation (27.26 ± 0.17%) compared with pure Al2O3 specimens. This indicated carbonized diamond particles had a positive effect on enhancing the ductility of Al2O3 ceramics. These scientific finding will provided an important reference for investigating additive manufacturing high-performance ceramics.  

    Tingting Li, Jiong Zhao, Jing Li, Yangli Xu, Zeling Yang, Xiaopeng Jiang, Luying Chen, Guangyao Han, Zihan Wang, Xuanyang Cao

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  • Abstract：Reliable n-type doping, defined here as dopant incorporation that provides a shallow donor ionization energy, sufficient electron activation at room temperature (approximately 300 K), structural stability, and compatibility with chemical vapor deposition/microwave plasma chemical vapor deposition (CVD/MPCVD) growth, remains a central obstacle to the implementation of diamond electronics. In this work, density functional theory calculations are used to examine the formation, stability, and electronic properties of BN2 defect complexes in diamond, with emphasis on feasible defect reaction pathways rather than experimental synthesis. Substitutional B–N complexes were evaluated in 64-, 216-, and 512-atom supercells, and the effect of residual strain was examined over the range from −0.10% to +0.10%. The BN2 complex exhibits a donor ionization energy of 0.132 eV based on charge-state total-energy analysis, consistent with its potential to support electron activation at approximately 300 K. Precursor-referenced reaction-energy analysis indicates that nitrogen-related precursor defects lower the energetic cost of BNx formation, while dissociation reaction-energy calculations show that BN and BN2 are thermodynamically more resistant to the considered neutral decomposition channels than nitrogen-rich BN3 and BN4 complexes. Strain modulates local B–N and B–C bonding and changes the dissociation energetics of BN2. The most favorable neutral route to BN2 formation is the reaction between BN and substitutional N defects, with a reaction energy of −1.04 eV in the 216-atom model. These results identify thermodynamically plausible routes for incorporating BN2 into diamond and provide guidance for precursor-, strain-, and temperature-controlled CVD/MPCVD growth of n-type diamond.  

    Zhang Dongliang, Hanyang Xu, Xiang Sun, Zhiyin Gan, Sheng Liu

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