Diamond exhibits highly promising properties for next-generation high-efficiency, high-frequency, and highpower electronic devices, while its practical implementation is severely hindered by high ionization energies of dopants, resulting in low room-temperature carrier densities and excessive resistivity. Recent studies have suggested that uniaxial strain can modulate diamond's band structure, narrow the bandgap and potentially inducing an indirect-to-direct transition, while it is not useful to reduce the ionization energy in N-doped diamond. Here, we applied biaxial strain, which is more compatible with practical device fabrication, on X-doped diamond (X = B, P, O, and N) and systematically investigated the effects of biaxial strain on the ionization energy of X-doped diamond using first-principles calculations. The results reveal that biaxial tensile strain significantly reduces ionization energies for all studied dopants. Even under a 3% biaxial tension, ionization energies decrease to 0.12 eV for B (64% reduction), 0.35 eV for P (37%), 2.21 eV for O (20%), and 1.24 eV for N (28%). These findings underscore the strong potential of biaxial strain engineering as a viable strategy for enhanced doping efficiency and improving electrical activation in diamond semiconductors. This work provides crucial theoretical insights to support the design and development of advanced diamond-based electronic devices.

It is very difficult to prepare vertical nanodiamond (VND) dominated sheets compared with vertical graphene (VG) sheets. Here, we describe the preparation of VNDs by phase transformation from Ta-loaded VGs via argon/oxygen plasma treatment with varied oxygen percentage. As the oxygen percentage increases to 5%, the height of VGs decreases, accompanied by high capacitance and low Hall mobility. When the oxygen percentage increases to 10%, the VGs transform to nanocrystalline diamond (NCD) grains with trans-polyacetylene (TPA) contents in grain boundaries increasing significantly. These VNDs exhibit both high capacitance (1452 μF cm-2) and n-type Hall mobility (846 cm2 V-1s-1). With the oxygen percentage increasing to 20%, NCD grains grow larger and the TPA content reduces, while the capacitance decreases considerably, but Hall mobility remaining high, suggesting that the performance improvement results from the synergistic effect of NCDs and TPA. These exhibit significant applications of VNDs in energy storage, high performance sensors, high-frequency and high-power electronic devices.

Free-standing diamond films have important applications in the fields of heat dissipation and optics. Conventional methods face challenges in efficiently separating high-quality and low-stress diamond films from common substrates such as Si and SiC while minimizing damage. This study introduces an electrochemical separation method for fabricating low-stress free-standing diamond films via ultrasonic-assisted thermal electrolysis of graphite substrates. Leveraging the excellent thermal expansion coefficient match with diamond, a three-step process has been developed: first, a uniform Ta2O5 intermediate layer was deposited on graphite via atomic layer deposition to ensure high-quality diamond growth; second, diamond films were grown by microwave plasma chemical vapor deposition; finally, the graphite substrate was selectively removed by ultrasonic-assisted thermal electrolysis in (NH4)2SO4 solution. Optimized electrolysis conditions (0.5 M (NH4)2SO4, 0.30 A (0.195 A/cm2), 3 h) more than 95% of the graphite substrate was removed while maintaining the structural integrity of the diamond film. Raman mapping performed over a 4 × 4 mm2 region revealed a relatively uniform residual stress distribution without pronounced macroscopic stress concentration, and the average residual stress was as low as −0.2327 GPa, indicating that the diamond film remained predominantly under compressive residual stress. This work presents a nondestructive pathway to produce large-area freestanding diamond films, advancing applications in high-power electronics and extreme optics.

Currently, Al2O3-based thermal interface materials (TIMs) have the most extensive industrial application for the thermal management of modern electronic devices. These TIMs are characterized by their low cost, ease of processing, high electrical insulation, but are limited by their thermal conductivity. The thermal performance bottleneck of Al2O3-based TIMs primarily stems from the extremely high interfacial thermal resistance at the micro/nano-scale interfaces between adjoining alumina fillers, a phenomenon resulting from the "point to point" dry contact established by the nature of solid spherical particles. To address this issue, herein, we have successfully developed a well-designed hybrid filler system, utilizing Al2O3 as the main thermally conductive filler and incorporating hexagonal boron nitride (h-BN) flakes and gallium-based liquid metal (LM), to significantly improve the through-plane thermal conductivity of the targeted TIMs. Specifically, a mechanochemical grinding process was utilized to promote the anchoring and spreading of LM on the Al2O3 surface, followed by a vertical compression that forced the h-BN flakes into good coverage and tight adhesion on the LM-modified alumina. As a result, not only did the contact mode between the fillers change from "point-to-point" to "face-to-face," but the "dry" contact also evolved into "liquid-solid" interface configurations with extremely low contact thermal resistance, thanks to the surface-anchored LM. Moreover, the h-BN flakes can also form a highly oriented arrangement during the pressing, thereby creating additional thermal conductive pathways that boast high heat transfer efficiency. Compared to the pure Al2O3-based composite, the TIM comprising 50 wt% Al2O3, 20 wt% h-BN, and 10 wt% LM, with soft polydimethylsiloxane (PDMS) as the matrix, demonstrates an impressive through-plane thermal conductivity of 7.2 +/- 0.30 W m-1 K-1, marking a significant improvement of 133 %. In the TIM performance test, the cooling efficiency of our sample is similar to 1.67 times that of the advanced commercial thermal pad. Additionally, it possesses a high volume resistivity of 5.6 x 1011 Q cm, a low dielectric constant of 2.15 at 106 Hz, and a low dielectric loss tangent of 0.0058 at 106 Hz. Our finding is believed to inspire others to prepare advanced TIMs with comprehensive properties via purposeful filler hybridization. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The filament pitch, a critical parameter in the hot-filament chemical vapor deposition of boron-doped diamond film electrodes, remains insufficiently studied. This work systematically investigates the influence of filament pitch (varied from 10 to 25 mm) on the microstructure, phase composition, and electrochemical properties of BDD films. The results demonstrate a non-monotonic relationship between electrode performance and filament pitch. As the pitch increases from 10 to 20 mm, grain refinement occurs, which significantly enlarges the electrochemically active surface area. Simultaneously, the films maintain a high sp3-carbon content and a wide potential window, synergistically resulting in a high oxygen evolution potential and low charge transfer resistance. However, an excessively large pitch of 25 mm introduces sp2-carbon phases. Although the specific surface area is further increased, this introduction of sp2 carbon severely compromises the film's electrochemical stability and catalytic activity. This work identifies an optimal filament pitch range of 15-20 mm, which achieves an optimal balance between grain refinement and phase purity. This finding provides crucial guidance for fabricating high-performance BDD anodes for electrochemical oxidation technologies.

The direct deposition of diamond coatings on zirconia substrates is hindered by a significant mismatch in thermal expansion coefficients (CTE). This study applied laser surface texturing to create microgrid structures on zirconia to relieve interfacial stress and enhance coating adhesion. Microcrystalline diamond (MCD) coatings were deposited by hot-filament chemical vapor deposition (HFCVD) on textured substrates with varying grid sizes. Through performance comparison, the optimal grid size of 0.2 mm was identified and used to fabricate microcrystalline, nanocrystalline (NCD), and ultrananocrystalline (UNCD) diamond coatings. The coatings were characterized and their tribological properties evaluated. Results show that textured zirconia with a 0.2 mm grid enabled crack-free, well-adhered diamond coatings. The microcrystalline diamond coating exhibited the highest wear resistance with a wear rate of 1.44 x 10- 6 mm3/N center dot m but a higher friction coefficient of 0.24. In contrast, the ultrananocrystalline diamond coating showed the lowest friction coefficient of 0.19 with a wear rate of 2.35 x 10-6 mm3/N center dot m. This study provides a viable strategy for designing diamond-coated zirconia components for marine wear applications.

The substantial thermal mismatch between zirconia and diamond poses a formidable challenge for the direct deposition of diamond film. In this study, we introduce a novel approach involving a carbonized transition layer, which enables the controllable and uniform growth of diamond film on the surface of zirconia substrates. First, a Si transition layer was deposited on the surface of a zirconia substrate using magnetron sputtering to improve the bonding strength between the diamond and the substrate. Subsequently, carbonization heat treatment was carried out to enhance the nucleation ability of the diamond film on the surface of the Si transition layer, thereby achieving the homogeneous and stable growth of the diamond film on the Si layer. Finally, time-resolved experiments revealed that diamond film evolve from homogeneous nucleation to island growth and coalescence, ultimately forming a continuous layered film.

Here, we reported a novel Y2O3/Si/diamond/Y2O3 composite material with high infrared (IR) transmittance and thermal-resistant performance. Diamonds on Si substrates were synthesized by microwave plasma chemical vapor deposition (MPCVD) method. The effects of nucleation density and diamond thickness on the optical transmittances were studied. Under the optimal seed density (1:3 dilution), the fabricated Si/diamond samples showed transmittance up to 59.5 %, very close to the theoretical value. After coating on both sides, the peak transmittance of the obtained Y2O3/Si/diamond/Y2O3 composites reached 95.6 % in the IR band (3-5 mu m). High transmittance was benefited from precise controlling the microstructural interface of Si/diamond, the thickness of diamond (below 100 mu m) and anti-reflective Y2O3 films (-600 nm). The sample showed no obvious crack or depression on the optical properties after rapid heating to 500 degrees C repeatedly. It therefore demonstrated the excellent optical property and heat-resistant performance. The present work supports the feasibility of applying the Y2O3/Si/diamond/Y2O3 composites as IR window under harsh conditions.

CO2 transforming into diamond enables a high-value conversion, while diamond growth is inhibited when the oxygen-to-carbon ratio exceeds 0.3. Here, we add Ar to improve the dissociation efficiency of CO2 and use optical emission spectroscopy (OES) to measure the intensity of C2 and H alpha species in a CO2-CH4-H2-Ar atmosphere and correlate their contents with diamond growth rate, diagnosing the indicator of rapid diamond growth and corresponding process parameters. The results show that in the case of O/C ratio of 0.5, with the Ar flow increasing to 70 sccm, both IC2/IH alpha value and the growth rate attain to the maximum, with the growth rate increasing from 2.1 mu m/h (without Ar) to 14.3 mu m/h. This discovers IC2/IH alpha as the indicator of rapid diamond growth. Subsequently, under this Ar flow, the OES were used to directly measure IC2 and IH alpha values under different process parameters without performing the real diamond growth. It indicates that the IC2/IH alpha value initially increased and then decreased with rising power, resulting in the maximum of IC2/IH alpha(max) appearing at a relatively low power (around 3000 W). Using the process parameters corresponding to the IC2/IH alpha(max) to grow diamond further increases the growth rate from 14.3 to 20 mu m/h at O/C ratio of 0.5, and in the case of O/C ratio reaching 0.917, the growth rate increased from nearly negligible to 3.1 mu m/h. All samples exhibit high quality with small diamond Raman FWHM value (less than 3 cm-1). This work holds significant importance for the industrialization of converting CO2 into diamond.

An Al-doped chromium nitride (Cr2N) film has demonstrated excellent interlayer properties in depositing high-adhesion diamond film on stainless steel due to high bonding strength which is ascribed to easy diamond nucleation and good mechanical properties and thermodynamic properties. However, the effect of Al addition on the properties and the underlying cause are unknown. In this work, the influence of Al contents on the structural stability, elastic, thermodynamic properties and electronic structure of Cr2N were studied by first principles calculations. The results show that the Young's modulus (E), bulk modulus (B) and shear modulus (G) of Cr2-xAlxN material all show a decreasing trend when Al content x is from 0 to 0.167, indicating that the deformation resistance decreases. At the same time, Poisson's ratio, Pugh criteria and Cauchy pressure all suggest that the brittleness of Cr2-xAlxN is reduced as x increases. The thermodynamic performance shows that the thermal stability of Cr2-xAlxN improves and thermal expansion coefficient rises as Al content increases. Debye temperature analysis shows that thermal stability and thermal conductivity of Cr2-xAlxN first decrease as x increases from 0 to 0.167, then increase with x larger than 0.167. The electronic structure reveals that the addition of Al increases the metallicity of Cr2N, thereby improving its toughness and adhesion of diamond film on stainless steel using Cr2-xAlxN interlayer. The work contributes to understanding an excellent interlayer property of Cr2-xAlxN film.

AbstractThe transformation of graphite into diamond (2–10 nm) at ordinary pressure by monodispersed Ta atoms was recently reported, while the effects of Ta concentration on the transition process remain obscure. Here, by regulating the Ta wire treatment time, as well as the annealing time and temperature, larger diamond grians (5–20 nm) are successfully synthesized, and the transition process of graphite to diamond is revealed to vary with Ta concentration. Specifically, short Ta wire treatments (5–10 min) induce graphite to form a “circle” structure and transforms into diamond directly after annealing. Long Ta wire treatments (15–25 min) produce larger and more “circle” structures, containing an increased number of graphite layers. After annealing at 1100 °C for 30–120 min, graphite first transforms into amorphous carbon, then to i‐Carbon and n‐Diamond, and finally to diamond. Notably, a large amount of n‐Diamond and diamond are formed after 120 min annealing. By modulating the annealing temperature from 500 to 1200 °C for 30 min, diamond is already obtained at 500 °C, and hexagonal diamond up to 20 nm in size at 1200 °C. This provides a fresh insight into the graphite/diamond transition process and an approach for diamond synthesis.

Transition metal carbides (TMCs) are frequently present alongside diamond during chemical vapor deposition processes and play a significant role in diamond formation. Inspired by this, we explore the potential of TMCs to promote the transition of bilayer graphene to diamane. Using first-principles calculations, we investigate the combined effects of pressure and surface chemistry on the conversion of bilayer graphene into two-dimensional diamond films, employing helium, TaC, and TiC as surface mediators. Our results reveal that TaC significantly enhances the phase transition to a diamane structure by promoting interlayer bonding in graphene, which stabilizes the dangling spa bonds. Specifically, TaC reduces the required conversion pressure to only 22.2 % of that needed without a chemical mediator, highlighting its substantial catalytic effect. Upon reducing the pressure to 0 GPa, the TaC-mediated system retains a stable diamane structure, with only a small amount of residual sp2 carbon remaining. In contrast, TiC forms weaker bonds with the graphene, leading to a diamane structure primarily stabilized by external pressure. Upon pressure release, this structure reverts to graphene. These findings highlight TaC as a highly effective catalyst for both the conversion and stabilization of graphene to diamane, while TiC, although aiding initial conversion, fails to maintain the diamane structure under decompression. Our study provides new insights into the role of catalytic surfaces and pressure in carbon phase transformations, offering potential strategies for the efficient fabrication of ultrathin diamond films.

The design of efficient heterojunctions for solar energy applications remains a significant challenge, particularly in optimizing charge separation and material stability for long-term performance. Here, we explore covalent Type-II heterojunctions formed by integrating diamond with graphene nanoribbons (GNRs), where electron density is modulated within the pi-bonds of graphene's six-membered rings. By tuning the GNR width and edge termination, the electronic structures of the heterojunctions can be systematically tailored. The resulting diamond-supported GNR (DS-GNR) heterojunctions generate a built-in electric field at the interface, enabling efficient separation of photogenerated electrons and holes and promoting interfacial charge transfer. Optical property analysis reveals strong visible-light absorption (similar to 105 cm-1), a broad absorption edge, effective charge separation, and light carrier effective masses, all of which are advantageous for photovoltaic applications. Furthermore, band alignment calculations demonstrate that several DS-GNR configurations meet the energy-level criteria for photocatalytic water splitting, highlighting their potential for solar-driven hydrogen production. Particularly, three-layer sp2-carbon GNRs form the desired Type-II alignment, with hydrogen-, hydroxyl-, and dihydrogen-terminated edges exhibiting suitable band positions for photocatalytic hydrogen evolution. These findings establish DS-GNR heterojunctions as promising candidates for both photovoltaic and photocatalytic energy conversion, offering design strategies for next-generation carbon-based materials in renewable energy technologies.

It is a key challenge to prepare two-dimensional diamond(2D-diamond).Herein,we develop a method for synthesiz-ing 2D-diamond by depositing monodisperse tantalum(Ta)atoms onto graphene substrates using a hot-filament chemical vapor deposition setup,followed by annealing treatment under different temperatures at ambient pressure.The results in-dicate that when the annealing temperature increases from 700 ℃ to 1000 ℃,the size of the 2D-diamond found in the samples gradually increases from close to 20 nm to around 30 nm.Meanwhile,the size and number of amorphous car-bon spheres and Ta-containing compounds between the graphene layers gradually increase.As the annealing temperature continues to rise to 1100 ℃,a significant aggregation of Ta-containing compounds is observed in the samples,with no dia-mond structure detected.This further confirms that monodisperse Ta atoms play a key role in graphene phase transition into 2D-diamond.This study provides a novel method for the ambient-pressure phase transition of graphene into 2D-diamond.

Traditional methods of transforming graphite into diamond, such as high-pressure, high-temperature techniques, require expensive equipment and conditions. Here, we present a novel method for synthesizing diamond from graphite at atmospheric pressure by employing magnetron sputtering to deposit tantalum (Ta) atoms onto graphite flakes, followed by hydrogen plasma treatment and annealing. Secondary ion mass spectrometry measurements confirm that the hydrogen plasma treatment incorporates hydrogen atoms into the graphite matrix and the content of tantalum oxide formed during the transfer from the sputter equipment to plasma treatment dramatically decreases after annealing. The x-ray photoelectron spectroscopy analysis reveals that the annealing process effectively reduces tantalum oxide in graphite to monodisperse tantalum atoms. As the annealing time increases, both the content of monodisperse Ta and the proportion of sp3 carbon structures rise. Transmission electron microscopy results show the formation of diamond grains with sizes ranging from 10 to 30 nm. This indicates that the increase in monodisperse Ta atoms facilitates the graphite-to-diamond transformation, suggesting that hydrogen-reduced Ta atoms play a key role in enhancing the efficiency of this phase transition. Our method offers a promising and cost-effective route for synthesizing diamond from graphite under atmospheric pressure.

Boron-doped diamond (BDD) electrodes are highly promising candidates for electrochemical CO2 reduction reactions (eCO2RR). However, the specific active sites responsible for eCO2RR on BDD electrodes remain contentious, primarily due to the limitations of traditional computational models, which overlook surface charge effects and explicit water molecules. These limitations impede the accurate characterization of the complex dynamics at the solid-liquid interface between the BDD surface and the electrolyte, presenting a significant challenge in optimizing the efficiency and selectivity of value-added product formation on BDD electrodes. In this study, we develop a BDD-H2O explicit solvent model by substituting B atoms at surface, sub-surface, and deeply embedded C atom sites, to elucidate the nature and underlying mechanisms of the active sites in eCO2RR on BDD electrodes under practical electrode potentials. Our computational results elucidate the reaction mechanism of formic acid formation on BDD surfaces and confirm that formic acid is the predominant reduction product under practical temperatures and potentials, consistent with previous reports. Our findings reveal that surface and subsurface B atoms in BDD are indispensable for CO2 reduction, while deeply embedded B atoms remain essentially inactive catalytically. Furthermore, our analysis reveals that the CO produced on BDD electrodes originates from the dissociation of carboxyl groups at the surface C atoms, while formaldehyde is more likely a secondary reduction product derived from surface-adsorbed CO. This study provides crucial mechanistic insights into eCO2RR on BDD electrodes and offers a foundation for their rational optimization, contributing to advancements in CO2 resource utilization.

The development of effective and robust electrochemical catalysts for the nitrogen reduction reaction (NRR) remains a substantial challenge for ammonia synthesis under mild conditions. In this study, we investigate the potential of single-atom d-block transition metals embedded within ZrO2 monolayers as catalysts for the NRR. Through advanced ab initio calculations, we elucidate a straightforward yet effective principle for describing the limiting potential of the NRR. Additionally, we identify two previously unreported and highly efficient electrocatalysts, Nb@ZrO2 and V@ZrO2, both of which demonstrate notably low limiting potentials of -0.3 V. Furthermore, these catalysts exhibit excellent selectivity and commendable stability. These results offer valuable insights for advancing research on high-performance NRR catalysts.