Hot-filament chemical vapor deposition (HFCVD) facilitates the realization of industrial mass production owing to its simple synthesis device, facile control of process conditions, and low preparation cost. Reactive pressure is one of the deposition parameters that exert a profound influence on the growth of HFCVD diamond films on polycrystalline diamond (PCD) substrates, primarily affecting the growth rate and grain size of the deposited diamond coating. A univariate experimental approach was employed to investigate the effects of reactive pressure (2 kPa, 3 kPa, 4 kPa, 5 kPa) on the properties of as-deposited diamond films. The results show that with the increase in reactive pressure, the growth rate increased first and then decreased, peaking at 5.366 μm/h at 3 kPa. The fractal dimension and grain size follow a similar variation trend, both decreasing first and then increasing. The grain size drops to 15.8 nm when the reactive pressure is 3 kPa, at which point the adhesive strength of the film is maximized. This phenomenon can be attributed to the fact that excessively low reactive pressure extends the mean free path of particles and active species, endowing them with higher kinetic energy and reducing collision-induced energy loss. This in turn significantly promotes diamond nucleation, secondary nucleation and grain refinement, thus facilitating the growth of nanocrystalline diamond. In contrast, an excessively high pressure yields the opposite effect, inhibiting nucleation and promoting grain coarsening.

Abstract This study explores the structural, chemical, and tribological behavior of boron-doped diamond coatings deposited on Ti-6Al-4V alloy substrates using hot filament chemical vapor deposition. The coatings were developed under optimized plasma-enhanced chemical vapor deposition conditions. Their characteristics were assessed through a combination of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and linear reciprocating tribological testing using silicon carbide (SiC) ball counter faces. XRD patterns confirmed the formation of nanocrystalline diamond layers, with prominent reflections corresponding to the (111), (220), and (311) planes. The suppression of diffraction signals from the underlying titanium alloy suggested uniform and complete coating coverage. Raman spectra showed a sharp sp3 carbon peak at 1332 cm−1, along with D and G bands typical of graphitic structures, indicating the presence of structural changes associated with boron doping. Friction and wear testing demonstrated a notably low coefficient of friction (∼0.0189) and a reduced wear-rate (∼4.02 × 10−5 mm3/N · min), marking a sixfold improvement over the uncoated alloy. Post-test SEM analysis revealed a dense, crack-free surface without signs of delamination. EDX analysis supported this observation, showing high carbon content (∼91.8%) and minimal detection of substrate elements. Furthermore, the wear track depth (110.4 µm) and SiC ball scar diameter (∼810 µm) were both significantly reduced in coated samples. These findings highlight the potential of boron-doped diamond coatings to enhance the surface durability, wear resistance, and mechanical stability of titanium-based materials, particularly for demanding applications such as biomedical implants.

Hot filament CVD growth of diamond sub-microcrystals with luminescent GeV− and SiV− color centers: parallel versus sequential doping with Ge and Si atoms

Diamond coatings with three distinct surface textures, namely spherical, pyramidal, and prismatic morphologies, were fabricated using the hot-filament chemical-vapor deposition (HFCVD) method. Scanning electron microscopy (SEM) was employed to analyze the surface morphological characteristics and differences among the coatings. Raman spectroscopic analysis further confirmed that all three diamond films exhibited excellent deposition uniformity and high crystalline quality. A three-dimensional optical microscopy system was used to measure the surface roughness values, which were determined to be Ra 0.423 μm, Ra 0.515 μm, and Ra 0.809 μm, respectively. An HFCVD diamond-coated tool was innovatively employed for the lapping of sapphire wafers, enabling a systematic investigation of the tribological behavior during the lapping process. Based on the experimental results, three morphological material removal models were established. The study demonstrates that the spherical diamond coating achieves a superior surface finish (Ra 0.22 μm) due to its continuous multi-point contact geometry, governed by the agglomerated nanocrystalline structure. Sample 3 had the highest removal rate of 24.3 μm/min. This is related to its surface morphology characteristics and is also due to the two-body contact between the diamond-coated tool and sapphire, offering a high-efficiency alternative for precision machining.

The integration of high-thermal-conductivity diamond films onto silicon carbide (SiC) substrates offers a promising pathway for thermal management in high-power electronic devices. Here, we investigate the depth-dependent thermal conductivity of a ∼5 μm-thick diamond film grown on SiC by hot filament chemical vapor deposition (HFCVD) using square-pulsed source thermometry. Electron backscatter diffraction and transmission electron microscopy reveal pronounced grain coarsening from the nucleation interface to the film surface. By combining frequency-dependent thermal penetration with a depth-resolved thermal transport model, we quantitatively reconstruct the thermal conductivity profile. The thermal conductivity increases sharply from ∼60 W m−1 K−1 near the nucleation region to ∼200 W m−1 K−1 at the surface, directly reflecting the underlying microstructural evolution. These results provide a physically grounded understanding of graded heat transport in HFCVD diamond and offer practical guidance for engineering diamond-based thermal management layers for next-generation power devices.

Aiming at the key problems of the material removal rate and surface integrity of existing tools in the lapping of sapphire hard and brittle crystals, an efficient lapping tool has been developed to explore a new process for HFVCD (hot filament chemical vapor deposition) diamond tools to efficiently lap sapphire wafers. With the premise of ensuring the surface roughness of the wafer is Ra ≤ 0.5 μm, the material removal rate is increased to more than 1 μm/h. To explore a high-efficiency lapping process for sapphire wafers using HFCVD diamond tools. The influence of key preparation parameters on the surface characteristics of CVD (chemical vapor deposition) diamond films was systematically investigated. Three types of CVD diamond coating tools with distinct surface morphologies were fabricated. These tools were subsequently employed to conduct lapping experiments on sapphire wafers in order to evaluate their processing performance. The experimental results demonstrate that the gas pressure, methane concentration, and substrate temperature collectively influenced the surface morphology of the diamond coatings. The fabricated coatings exhibited well-defined grain boundaries and displayed pyramidal, prismatic and spherical features, corresponding to high-quality microcrystalline and nanocrystalline diamond layers. In the lapping experiments, the prismatic CVD diamond coating tool exhibited the highest material removal rate, reaching approximately 1.7 μm/min once stabilized. The spherical diamond coating tool produced the lowest surface roughness on the lapped sapphire wafers, with a value of about 0.35 μm. Surface morphology-controllable diamond tools were used for the lapping processing of the sapphire wafers. This achieved a good surface quality and high removal rate and provided new ideas for the precision machining of brittle hard materials in the plane or even in the curved surface.

Seaweed-like carbon micro-nano structure on Ni foam by hot filament chemical vapor deposition in an Ar/CH4/H2 gas mixture

Cathodoluminescence of n-type diamond films grown by hot-filament chemical vapor deposition: Effects of hydrogen concentration

Polycrystalline diamond is a promising material for MEMS resonators due to its remarkable mechanical and electrical properties and compatibility with standard semiconductor manufacturing processes. However, the growth on non-diamond substrates is challenging, and a seeding process is needed to grow closed thin films. Hot filament chemical vapor deposition and reactive ion etching are powerful tools to deposit and micromachine diamond thin films on silicon substrates. In this paper, a polycrystalline diamond thin film with micrometer-sized grains is used to fabricate MEMS resonator devices, and quality factors are measured using laser Doppler vibrometry. The resonator’s bottom and top sides, as well as the cross sections, are investigated, and a substrate-near region with an elevated amount of non-diamond carbon bonds is identified with TEM in the energy-filtered transmission electron microscopy mode. By monitoring the quality factors of several resonance modes of 142 MEMS resonator devices, while a reactive ion etching treatment is performed at the bottom side of the resonators, we find an initial increase in the mean quality factor of all out-of-plane modes in the frequency spectrum from 20 to 500 kHz by nearly a factor of 3 after 28 min of back thinning of an initially 2.2 μm thick polycrystalline diamond thin film due to the reduction of the defect-rich substrate-near region. Even more, we find no correlation between surface roughness and quality factor, indicating losses at structural defects, such as grain boundaries and non-diamond carbon clusters, as dominant for energy dissipation.

A significant development in material science is thin film deposition based on hot wire techniques, commonly referred to as Hot-Wire Chemical Vapour Deposition (HWCVD) or Hot-Filament Chemical Vapour Deposition (HFCVD). This process creates high-quality thin films on a variety of substrates by effectively breaking down precursor gases using heated filaments. It is an essential tool for a wide range of applications, from innovative microelectronics to sophisticated solar cell technologies and durable protective coatings, its special qualities, which include plasma-free functioning and low substrate temperature requirements. Plasma-Free Precision Because HWCVD does not use plasma, bombardment is reduced, and complex film structures and delicate substrates are shielded from harm a crucial benefit for sensitive applications. Versatile Material Spectrum is extensive applicability demonstrated by its ability to deposit a variety of materials, such as silicon-based films (amorphous, nanocrystalline), silicon nitride, different polymers, diamond-like carbon, and even graphene. Industrial Scalability and Efficiency of HWCVD provides an economically viable and scalable alternative for industrial manufacturing, frequently outperforming conventional methods in efficiency thanks to its high deposition rates and capacity for large-area and roll-to-roll processing.

Boron-doped diamond (BDD) is an excellent electrode material for electrochemical sensors and both high sp3/sp2 carbon component ratios and high boron concentrations are significant factors for specific applications. Hot-filament chemical vapour deposition (HFCVD), which is a conventional technique for synthesising large and uniform BDD electrodes for industrial applications, presents challenges when synthesising films with the above characteristics. In this study, we demonstrate the stable long-term synthesis of heavily boron-doped polycrystalline diamond with a high sp3/sp2 ratio by adding CO2 gas and adjusting the H2/CH4/B(CH3)3/CO2 gas ratio during HFCVD. Adding an appropriate amount of CO2 gas not only reduces the sp2 carbon component but also improves crystallinity and increases growth rate while maintaining metallic conductivity despite a moderate decrease in boron concentration. Electrochemical measurements reveal that our BDD electrodes exhibit excellent characteristics comparable to those of high-standard BDD electrodes synthesised using microwave plasma-assisted CVD.

Nanocrystalline diamond (NCD) films deposited through chemical vapor deposition (CVD) possess exceptional properties, making them highly useful in various technological applications, including tribology in extreme conditions. The research starts with the deposition of CrN interlayer coatings on an M50 steel substrate using an RF magnetron sputtering followed by NCD film deposition on a steel M50 using Hot-Filament CVD (HFCVD). The resulting coatings were evaluated for their tribological, mechanical, and corrosion resistant properties. Results indicate that the H/E (coating’s ability against elastic deformation) and H 3 /E 2 (resistance to plastic deformation) ratio increases with applied load. The NCD coating demonstrated exceptional corrosion protection, achieving an efficiency of 82.4%. These findings suggest that NCD coated M50 steel offers a reliable solution for complex tribological applications, particularly in the aerospace and marine sectors.

Conductivity sensors play a vital role in monitoring production data in oil wells to ensure efficient oilfield operations, and their service performance depends on the durability of Invar alloy electrodes. The alloy electrodes are susceptible to damage from abrasive solid particles, corrosive media, and oil fluids in downhole environments. The degradation of the alloy electrodes directly compromises the signal stability of conductivity sensors, resulting in inaccurate monitoring data. Inspired by the intrinsic oleophobic properties of fish scales, we developed a fluorinated boron-doped diamond (FBDD) film with biomimetic micro–nano structures to enhance the wear resistance, corrosion resistance, and amphiphobicity of Invar alloy electrodes. The fish scale architecture was fabricated through argon-rich hot-filament chemical vapor deposition (90% Ar, 8 h) followed by fluorination. FBDD-coated electrodes surpass industrial benchmarks, exhibiting a friction coefficient of 0.08, wear rate of 5.1 × 10−7 mm3/(N·mm), corrosion rate of 3.581 × 10−3 mm/a, and oil/water contact angles of 95.32°/106.47°. The following underlying improvement mechanisms of FBDD films are proposed: (i) the wear-resistant matrix preserves the oleophobic nanostructures during abrasive contact; (ii) the corrosion barrier maintains electrical conductivity by preventing surface oxidation; (iii) the oil-repellent surface minimizes fouling that could mask corrosion or wear damage.

• Successful immobilization of ASNase on boron-doped diamond (BDD) surfaces was achieved. • Functionalized surfaces boost ASNase immobilization yields to 68% vs. 17% untreated. • Amine-terminated BDD surfaces retain 54% enzyme activity after 3 cycles. L-asparaginase is an enzyme with diverse and significant applications, such as reducing acrylamide formation in starchy food processing and as a biopharmaceutical for treating acute lymphoblastic leukaemia. However, the free enzyme is susceptible to external factors, leading to reduced stability compared to its immobilized forms. L-asparaginase was adsorbed onto both amine- and oxygen-terminated boron-doped diamond surfaces under controlled conditions (pH 8, 37 °C, 0.06 mg/mL ASNase, and 1 h immobilization on 5 × 5 mm boron-doped diamond surfaces). Boron-doped diamond surfaces were grown from hot-filament chemical vapor deposition. The results show a successful enzyme immobilization, with the amine- and oxygen-terminated surfaces exhibiting an enhanced immobilization yield of up to 68%, compared to just 17% on untreated as-grown boron-doped diamond. Notably, amine-terminated boron-doped diamond surface maintained 54% of its initial relative activity after three cycles of reaction, outperforming other diamond surfaces. This work demonstrates the potential of boron-doped diamond surfaces for immobilizing and reuse of L-asparaginase through simple adsorption, which could be valuable for future biosensing applications.

ABSTRACT Hot Filament Chemical Vapour Deposition (HFCVD) is a promising method for producing low-pressure diamond coatings, offering simplicity, scalability, and cost-effectiveness. These studies examine the effect of chamber pressure, filament temperature, and pre-treatment on nucleation, morphology, and wear performance of CVD diamond coatings on tungsten carbide (WC) tool inserts. SEM (Scanning Electron Microscope) micrographs showed that crystal size and uniformity depend on deposition temperature and pressure. XRD (X-ray Diffraction) confirmed crystalline diamond deposition through a sharp (111) reflection diamond peak. µ-RS (Micro Raman Spectroscopy) confirmed a high-quality diamond phase with negligible graphitic contamination. Acid pre-treatment and diamond seeding were essential for successful nucleation and film integrity. Optimal deposition occurred at 2050°C filament temperature and 30 Torr chamber pressure, resulting in a homogeneous coating. CVD-diamond coated tools exhibited highest VHN (Vickers microhardness number) and least abrasive wear when machining aluminium versus uncoated tools under identical machining conditions (parameters such as feed rate, cutting speed, and depth of cut were taken the same for both the tools). These findings demonstrate HFCVD diamond coatings’ effectiveness for improving cutting tool durability, particularly in non-ferrous metal machining.

A method is reported to produce patterns of diamond using electron-beam lithography, polymer-assisted seeding, and hot filament chemical vapor deposition (HFCVD). Seeded stripes range from 200 nm to 9 µm in width. Separation is varied to examine isolated and merged lateral growth. Scanning transmission electron microscopy (STEM) images confirm the growth of micron-scale polycrystals that grow vertically over the seeded areas and extend laterally over unseeded regions. The resulting diamond was studied using scanning electron and atomic force microscopies. The vertical diamond growth rates range between 0.46 and 0.56 µm/h. Lateral growth rates show decreasing trend, from 0.48 to 0.20 µm/h, as initial seeding stripe widths increase. The results show that decreasing the initial seeding stripe width increases the lateral growth rate with comparable crystal quality. The effect of the gap between seeding stripes on the growth rates has been investigated in the range where separations are “large” for producing substrate coverage that is primarily direct growth on the unseeded substrate area. Ultraviolet (UV) micro-Raman line scans were used to examine the diamond grown directly on the seeded regions and the lateral growth over the unseeded substrate. Micro-Raman stress maps confirm the grown diamond to be directly bonded to the substrate where lateral overgrowth has taken place.

There are two conventional methods for growing synthetic diamonds on a scale of one centimeter or larger. One is the chemical vapor deposition (CVD) method, which includes plasma-assisted and hot-filament CVD and is used to create diamond films. The other method is high-pressure high-temperature (HPHT) growth, which accounts for approximately 99% of the synthetic diamonds produced annually[1]. In the HPHT method, carbon dissolved in liquid metals forms diamonds under pressures of 5-10 GPa and at temperatures ranging from 1300-1600 °C.There is a prevailing paradigm that diamond can be formed in liquid metals only under HPHT conditions because diamond is thermodynamically stable in this regime. It's worth noting that the diamonds produced using HPHT are usually limited to sizes of about one cubic centimeter due to the components involved. Discovering alternative methods to make diamonds in liquid metals under lower pressures is an intriguing basic science challenge that, if achieved, could revolutionize diamond manufacturing.In this talk, I would like to present our recent results on growing diamonds using liquid metals. We developed a liquid metal alloy composed of 77.75/11.00/11.00/0.25 atomic percentages of Ga/Ni/Fe/Si, which facilitates the growth of diamond crystals (hundreds of nanometers in size) and polycrystalline diamond films (a few millimeters in lateral size) using methane at 1 atm pressure and 1025 °C. This challenges the traditional growth model of diamonds[2]. The diamonds were observed growing within the subsurface regions of the liquid metal. We found that carbon becomes 'supersaturated' in the subsurface, leading to the nucleation and growth of diamonds, and that Si atoms play a critical role in stabilizing sp3-bonded carbon clusters, which triggers nucleation.Our growth method offers significant flexibility in the composition of liquid metals; for example, diamonds can also be grown using Ga/Co/Fe/Si and Ga/In/Ni/Fe/Si liquid alloys. It is likely that liquid metal alloys of other compositions would also work for growing diamonds.

Influence of the crystal size and chemical composition on the optical properties of diamond films grown by hot filament chemical vapor deposition

This study synthesized boron-doped diamond (BDD) thin films using hot-filament chemical vapor deposition at different carbon-to-hydrogen (C/H) ratios in the range of 0.3-0.9%. The C/H ratio influence, a key parameter controlling the balance between diamond growth and hydrogen-assisted etching, was systematically investigated while maintaining other deposition parameters constant. Microstructural and electrochemical analysis revealed that increasing the C/H ratio from 0.3% to 0.7% led to a reduction in sp2-bonded carbon and enhanced the crystallinity of the diamond films. The improved conductivity under these conditions can be attributed to effective substitutional boron doping. Notably, the film deposited at a C/H ratio of 0.7% exhibited the highest electrical conductivity and the widest electrochemical potential window (2.88 V), thereby indicating excellent electrochemical stability. By contrast, at a C/H ratio of 0.9%, the excessively supplied carbon degraded the film quality and electrical and electrochemical performance, which was owing to the increased formation of sp2 carbon. In addition, this led to an elevated background current and a narrowed potential window. These results reveal that precise control of the C/H ratio is critical for optimizing the BDD electrode performance. Therefore, a C/H ratio of 0.7% provides the most favorable conditions for applications in advanced oxidation processes.

Effects of substrate temperature on the characteristics of boron- doped single crystal diamond epilayers grown by hot filament chemical vapor deposition