Hot Filament Chemical Vapor Deposition Research Articles

A Simulation Study on the Effect of Filament Spacing on the Temperature Field Uniformity of an HFCVD System

Hot-filament chemical vapor deposition (HFCVD) has become the most widely used ways of preparing diamond film-coated tools due to the simple equipment used, its convenient operation, and its low cost. In the production process of an actual factory, a large number of coated tools need to be prepared in batches. Factors such as the hot-filament arrangement often affect the uniformity of coating on tools, making the performance of the tools prepared in the same batch unstable. This article uses ANSYS R15.0 software software in the context of computational fluid dynamics (CFD) to calculate the temperature field in the HFCVD system, and study the effect of filament spacing on the uniformity of the temperature field of the surface of the substrate. It was found that when the distance between filaments was 14 mm, 10 mm, 10 mm, 8 mm, 8 mm, the temperature field on the surface of the substrate was the most uniform. The experiments are consistent with the results of the simulation, indicating that simulation research has practical significance.

Effect of boron doping levels on the piezoresistive properties of boron-doped diamond films prepared by HFCVD

The exceptional piezoresistive properties of boron-doped diamond (BDD) films render them highly promising for pressure sensor applications. These properties are closely associated with the doping concentration, crystal structure, and substrate material. In this study, BDD films with varying boron concentrations (B/C=500-8000 ppm) were fabricated on silicon and diamond substrates using hot-filament chemical vapor deposition (HFCVD) equipment. The relationship between surface grain characteristics, grain boundaries, and gauge factor (GF) of BDD films deposited on different substrates was systematically examined. The concentration of boron doping significantly influenced the surface morphology, electrical resistivity, and GF of the BDD films. The grain size of BDD films initially increased as the boron doping concentration was raised from 500 ppm to 2000 ppm; however, it subsequently decreased when the boron doping content exceeded 2000 ppm. Moreover, we found that the piezoresistive impact of a BDD film is strongly correlated to its grain size; larger grain sizes result in higher GF values. Notably, compared to those on silicon substrates, the BDD films deposited on diamond substrates exhibited superior piezoresistive characteristics. Specifically at a doping concentration of 2000 ppm, a GF as high as 284 was achieved for the BDD film on a diamond substrate compared to only 140 for that on a silicon substrate.

Correlation of residual stress on piezoresistive properties of boron-doped diamond films

To investigate the influence of residual stress on the piezoresistive behavior of boron-doped diamond (BDD) films, BDD films with varying doping concentrations were synthesized using a hot-filament chemical vapor deposition (HFCVD) system on silicon and diamond substrates. The relationship between the surface morphology, structural composition, resistivity, and piezoresistive properties of BDD electrodes was examined, along with an in-depth analysis of the impact of boron doping level on these properties. The microstructure and bonding state of the BDD films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. The piezoresistive properties of the BDD films were evaluated employing a cantilever beam bending method. Our findings demonstrate that the level of boron doping not only affects resistivity but also directly influences residual stress in BDD films, both factors having an impact on their piezoresistive properties. Despite significantly larger grain sizes observed in BDD films grown on diamond substrates compared to those grown on silicon substrates at identical boron doping concentrations, they exhibit consistent variations in residual stress and gauge factor (GF) values. With increasing doping levels, the absolute residual stress decreases initially before increasing again; moreover, at 2000 ppm doping level, it transitions from compressive to tensile stress. The GF value is closely associated with both the magnitude and type of residual stress. By utilizing a doping concentration of 2000 ppm for growth on diamond substrates, we achieved a peak GF value of 257 for BDD films which highlights their promising potential for pressure sensor applications.

Preparation, wear resistance, and impact toughness of homoepitaxial diamond film deposited on polycrystalline diamond compact by HFCVD method

To minimize the detrimental effects of cobalt binder on the thermal stability of polycrystalline diamond compact (PDC) under high temperature working conditions and enhance the PDC’s properties. Hot filament chemical vapor deposition diamond coated polycrystalline diamond compact (HFCVD-PDC) was prepared by depositing homogeneous epitaxial diamond film on the polycrystalline diamond layer (PCD layer) treated with cobalt binder removal. The effect of deposition pressure on the microstructure of the diamond film was investigated, and the PDC’s wear resistance was assessed using the abrasion ratio test. The drop hammer impact test was utilized to evaluate the impact toughness of the original PDC, cobalt removal PDC, and HFCVD-PDC. The results showed that a continuous and dense nanodiamond film with a cauliflower-like structure was formed on the PDC surface at the deposition pressure of 3 kPa. The abrasion ratio of the HFCVD-PDC increased by 67.44% compared to the original PDC, and by 33.29% compared to the cobalt removal PDC. Furthermore, filling nanodiamonds into the pores of cobalt removal PDC improved its impact toughness. These findings suggest that the application of homogeneous epitaxial diamond on the PCD layer can significantly improve the PDC’s wear resistance and impact toughness.

Mass production and cutting performance of diamond coated cutting tools for machining titanium alloys

Diamond coated cutting tools are applied for machining difficult-to-machine materials of titanium alloys. However, the temperature field uniformity needs to be further improved for the mass production of diamond coated tools using the hot filament chemical vapor deposition (HFCVD) method. In this paper, the tools temperature distribution is simulated by the finite volume method (FVM) during the deposition of diamond coatings. An optimization method of deposition setting with fine filaments in dense arrangement (FFDA) is proposed, and the temperature distributions of the tools under the coarse filament in sparse arrangement (CFSA) and FFDA are simulated to systematically elucidate the effects of fine filament densification. Subsequently, the different hot filament arrangements are adopted to mass production experiment for deposition of micro/nano composite diamond (MCD/NCD) coatings on WC-6%Co cutting tools. In addition, the cutting experiments on titanium alloys are conducted using diamond coated tools, and the cutting performance of tools at different locations is evaluated. The results indicate that the FFDA method can improve the temperature field uniformity of mass-produced diamond coated cutting tools, and the cutting tools have better consistency in surface morphology, thickness, chemical composition, surface roughness and cutting performance.

Effect of oxygen doping on cutting performance of CVD diamond coated milling cutters in zirconia ceramics machining

Diamond thin films were deposited on WC-Co tools using the hot-filament chemical vapor deposition (HFCVD) technique at varying pressures and oxygen doping levels. As the oxygen doping content increased, the purity of the diamond phase improved, and the density of the <111> crystal plane on the film's surface increased. The growth rate of diamond films initially increased and then decreased under low pressure, with a corresponding decrease in residual compressive stress. Conversely, at high pressure, increased oxygen doping enhanced the diamond phase purity and growth rate while reducing residual compressive stress. Cutting experiments on pre-sintered zirconia ceramics for milling linear slots and engraving dentures demonstrated that diamond-coated milling cutters exhibited superior cutting performance under consistent oxygen and carbon source concentrations and stable air pressure conditions. The oxygen-doped diamond-coated milling cutter grown at a pressure of 1 KPa exhibited the longest service life, attributed to its reduced surface roughness, lower cutting force, and increased density of the <111> crystal plane orientation. This cutter could machine up to 1300 crowns, making it approximately 80% more durable than non‑oxygen-doped diamond-coated milling cutters and about 20 times more durable than uncoated ones.

Correlation between photoluminescence and radiative defects in silicon oxycarbide films due to the growth temperature effect

In this work, the effect of growth temperature (678–988 °C) on silicon oxycarbide (SiCxOy) samples obtained by hot filament chemical vapor deposition (HFCVD) is reported. The samples were deposited on silicon (Si) n-type (100) and quartz substrates for optical and structural studies. At a lower temperature (678 °C), silicon oxycarbide powders were formed on Si substrates due to the homogeneous reaction occurring in the gas phase. However, for temperatures between 804 and 988 °C, silicon oxycarbide films were formed on Si substrates. By changing the temperature from 678 to 988 °C, both carbon (C) concentration (21.2–17.7 wt.%) and the relative percentage of Si–C bond density (%RtSi-C = 11.34–3.47 %) decreased, as demonstrated by EDS and FTIR measurements, respectively. On the other hand, the content of relative Si–O–Si bonds located around 1060 cm−1 remained dominant in all cases, resulting in SiCxOy films with an amorphous SiOx-type structure. These films exhibited strong photoluminescence (PL) centered in the blue region (∼3 eV), where Si–NOVS radiative centers were preferentially responsible for PL emission. At a lower temperature (678 °C), the PL intensity decreased. The determination of optical bandgap energy (Eopt) using Tauc Plots coincided with the emission due to luminescent centers (∼3 and ∼2.7 eV) observed in PL, indicating that the radiative transitions were due to defects. The AFM measurements showed an increase in roughness from 5.01 to 16.20 nm as the growth temperature decreased, as expected according to SEM measurements.

Numerical simulation and experimental researches on different abrasive grain arrangements of monolayer diamond grinding tools fabricated by HFCVD method

The hot filament chemical vapor deposition (HFCVD) method has been used to fabricate monolayer diamond grinding tools, whose abrasive grain arrangements can be achieved by patterned masks. The orderly arrangement pattern of abrasive grains can improve the grinding trajectory density of abrasive grains and reduce the workpiece surface roughness. In this study, the numerical simulation method is used to investigate the effect of abrasive grain pattern arrangements on the grinding trajectories and ground surface topographies, including Archimedes spiral, concentric circular, phyllotactic, disordered, and staggered patterns. The simulation results indicate that the grinding trajectory is most uniform and dense when applying the staggered pattern arrangement, and the workpiece surface roughness is lower than that of the other pattern modes. Then monolayer diamond grinding tools with five types of abrasive grain patterns are fabricated on the SiC substrate by HFCVD method. The grinding tool surface has a complete grain pattern and as-grown diamond film on the substrate is homogeneous in thickness, which is regarded as the bonding layer of the abrasive tools. EDS carbon element mapping and Raman spectra analysis reveal that the as-grown diamonds, both on substrates and seeds, exhibit high quality. Grinding experiments are performed utilizing CVD diamond grinding tools. The ground surface with a staggered pattern exhibits the lowest surface roughness without periodic grinding bands, as is consistent with the simulation results. Besides, the graphitization evaluation and worn feature statistics show that abrasive grains are of low levels of graphitization and high quantity of dynamic active grains as well as have slight abrasive grain wear and large chip space applying staggered pattern, which is the ideal abrasive grain arrangement pattern.

Construction and characteristics of a thermometer in a hot filament CVD reactor for synthesis of nanocomposites based on carbon nanotubes

Construction and characteristics of a thermometer in a hot filament CVD reactor for synthesis of nanocomposites based on carbon nanotubes

Influence of the Incorporation of Nd in ZnO Films Grown by the HFCVD Technique to Enhance Photoluminiscence Due to Defects

In this work, optical–structural and morphological behavior when Nd is incorporated into ZnO is studied. ZnO and Nd-doped ZnO (ZnO-Nd) films were deposited at 900 °C on Silicon n-type substrates (100) by using the Hot Filament Chemical Vapor Deposition (HFCVD) technique. For this, pellets were made by from powders of ZnO(s) and a mixture of ZnO(s):Nd(OH)3(s). The weight percent of the mixture ZnO:Nd(OH)3 in the pellet is 1:3. The gaseous precursor generation was carried out by chemical decomposition of the pellets using atomic hydrogen which was produced by a tungsten filament at 2000 °C. For the ZnO film, diffraction planes (100), (002), (101), (102), (110), and (103) were found by XRD. For the ZnO-Nd film, its planes are displaced, indicating the incorporation of Nd into the ZnO. EDS was used to confirm the Nd in the ZnO-Nd film with an atomic concentration (at%) of Nd = 10.79. An improvement in photoluminescence is observed for the ZnO-Nd film; this improvement is attributed to an increase in oxygen vacancies due to the presence of Nd. The important thing about this study is that by the HFCVD method, ZnO-Nd films can be obtained easily and with very short times; in addition, some oxide compounds can be obtained individually as initial precursors, which reduces the cost compared to other techniques. Something interesting is that the incorporation of Nd into ZnO by this method has not yet been studied, and depending on the method used, the PL of ZnO with Nd can increase or decrease, and by the HFCVD method the PL of the ZnO film, when Nd is incorporated, increases more than 15 times compared to the ZnO film.

Long-lasting BDD/Si3N4–TiN electrodes for sustainable water remediation

Boron-doped diamond (BDD) thin films have the potential to revolutionize water remediation through electrochemical oxidation, converting persistent pollutants into CO2 and water. However, a significant challenge in implementing BDDs on a large scale is the choice of substrate material. Electrode failure typically occurs due to BDD delamination from the substrate. We propose using a ceramic composite of silicon nitride (Si3N4) and titanium nitride (TiN) as a substrate to address this issue. This electroconductive composite combines Si3N4's high wear resistance, chemical stability, and high affinity for diamond film growth with the TiN's metal-like conductivity. In this work, BDD films were grown by Hot Filament Chemical Vapor Deposition (HF-CVD) over Si3N4–TiN substrates containing 30%vol. TiN. The resulting BDD/Si3N4–TiN electrodes were analyzed concerning their microstructure, diamond quality, conductivity, adhesion strength, service life, and electrochemical properties. Phenol was used as a model to test the electrode's ability to oxidize pollutants. We found that the BDD/Si3N4–TiN electrode could eliminate phenol entirely and up to 98.8 % of the model solution's Chemical Oxygen Demand (COD) after 5 h of direct anodic oxidation, with an Average Current Efficiency (ACE) of 14 % and an energy consumption of 138 kW h kgCOD−1. Furthermore, the BDD/Si3N4–TiN electrode could withstand more than 2016 h of accelerated life test without film delamination. Overall, the results demonstrate that BDD/Si3N4–TiN electrodes are a potential long-lasting solution for large-scale water treatment by electrochemical advanced oxidation processes (EAOPs) in a sustainable manner, especially if combined with renewable energy sources.

Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS

Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS

Multimethod cross-sectional characterization approaching the limits of diamond monophase multilayers

Chemical vapour deposited diamond draws significant scientific interest due to its wide range of mechanical and functional properties, which can be easily tuned by the applied deposition conditions. Here, hot filament chemical vapour deposition was used to synthesize four monophase multilayer diamond thin films with individual layer thickness down to ∼ 300 nm. Extensive structural characterization by scanning electron microscopy and Raman spectroscopy on the cross-section confirmed the different diamond morphologies originating from the different applied process parameters of the individual sublayers, where Raman spectroscopy could give a clear distinction between nano- and microcrystalline diamond down to a layer thickness of ∼ 1 μm. Cross-sectional X-ray nanodiffraction identified exclusively the diamond crystal structure throughout the cross-section of the multilayered diamond thin films. Cross-sectional phase and FWHM analysis allowed to discriminate between the diamond morphologies down to ∼ 500 nm, thus identifying the limitations of monophase diamond multilayers. While the microcrystalline diamond sublayers all exhibit pronounced structural gradients expressed in (i) increasing intensity of the 111 Debye-Scherrer ring, (ii) ⟨110⟩ fibre texture, and periodic variations of (iii) grain size and (iv) residual stress, the nanocrystalline diamond sublayers showed no pronounced cross-sectional variations. In summary, the experimental results provide insights into the cross-sectional evolution of microstructure and residual stress and the limitations of monophase multilayered diamond thin films.

Hydrogenated graphene systems: A novel growth and hydrogenation process

Octadecylphosphonic acid self-assembled monolayers were used as a combined carbon and hydrogen source to grow graphene films on sapphire substrates via hot filament chemical vapor deposition. The functionalized substrates were sealed with a thin Cu film and heated to 950°C under Ar flow. After synthesis, the Cu was etched away. The graphene samples then underwent a hydrogenation treatment in the same reactor setup, exposed to a CH4/H2 gas mixture at 820°C for 2 hours. The structure and properties of the graphene films before and after hydrogenation were characterized. Raman spectroscopy was employed to probe the defect-related bands and C-H bonding. X-ray diffraction provided insights into the crystalline structure and interlayer spacing. The ferromagnetic response was measured using a PPMS system across a range of temperatures and magnetic fields. XPS was used to assess the chemical composition and bonding. This multi-step process enabled a detailed evaluation of the novel synthesis protocol and its effects on the resulting hydrogenated graphene material.

Corrosion resistance of diamond films with different grain sizes

Titanium alloys are widely used in the aerospace industry due to their excellent comprehensive properties. However, as the application becomes more and more extensive, higher requirements are put forward for the corrosion resistance of titanium alloys. Due to its natural chemical stability, diamond has become a good corrosion-resistant material. Diamond films with three different grain sizes were prepared on the surface of titanium alloy by hot-filament chemical vapor deposition (HFCVD). The protective efficiency of the three kinds of films to the substrate is above 90 %. The corrosion resistance of the nanocrystalline diamond (NCD) films is obviously better than that of the microcrystalline diamond (MCD) films. For NCD films, as the diamond grain size decreases, a cluster structure of particle stacking is formed, which hinders the arrival of corrosive substances to the substrate and further improves the corrosion resistance.

Tribological properties of HFCVD diamond coatings over wide temperature range

Single and gradient multilayered diamond coatings, deposited on silicon nitride (Si3N4), were prepared by hot filament chemical vapour deposition. The tribological properties were evaluated in a wide temperature range (26 °C–300 °C), against Si3N4 ceramic balls, as the friction counterpart. The results showed that with the increase of temperature from 26 °C to 300 °C, the wear rate of NCD (nanocrystalline diamond) and GCD (gradient diamond) coatings rapidly increases. When the temperature reaches 300 °C, obvious cracks and detachment appear on the surface of the NCD coatings. Due to the special interlayer, the wear rate of the GCD coatings is lower than that of the NCD coatings. In the range of 26 °C to 100 °C, GCD exhibits excellent wear resistance and low friction coefficient due to its special gradient structure. When the temperature increases to 200 °C, NCD films with smaller grain sizes exhibit higher wear rates. From the wear morphology, it can be seen that cracks are generated in the NCD film, and as the temperature increases, the cracks continue to expand until the film spalling. GCD shows relatively good wear resistance at high temperatures. This study found that gradient multilayered diamond coatings exhibited superior wear resistance at high temperatures, compared with single-layer coatings tested in identical conditions.

Nanostructured boron-doped diamond electrodes for two-electron water oxidation to produce hydrogen peroxide

Boron-doped diamond (BDD) electrodes have been widely used in water treatment, e.g., degradation of antibiotics and pigments for water purification. Hydrogen peroxide production by two-electron electrochemical oxidation of water is a green and attractive method that has the potential to replace the conventional anthraquinone autoxidation (AO) process. In this study, BDD films were prepared on single-crystal silicon wafers by using hot-filament chemical vapor deposition (HFCVD) technique. Then, dense tubular nanostructure (nanotubes) arrays were prepared on the BDD films employing inductively coupled plasma (ICP) etching. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) proved the formation of oxygen-terminated nanostructures, which was ascribed to the oxygen plasma and the self-masking. The length of diamond nanotubes as well as the root diameter increased gradually and non-linearly with the increase of etching time. It was indicated by cyclic voltammetry (CV) analysis that the effective active area of the electrodes increased after etching, and variations of resulting reaction performance were observed. The oxygen-terminated and nanostructured BDD electrode obtained by etching with the optimized parameters features better electrocatalytic performance, with reduced oxidation potential and 46.8 % higher Faraday Efficiency (FE) for hydrogen peroxide production, compared to the original BDD sample. Therefore, the manufacturing of nanostructures is an effective method to improve the efficiency of BDD water oxidation for the production of hydrogen peroxide.

Fabrication of diamond film under low methane concentration by hot filament chemical vapor deposition with magnetic field assistance

This study focused on improving diamond film growth through hot filament chemical vapor deposition (HFCVD) with an innovative method, magnetic field assistance. The effects on diamond films were thoroughly investigated using a combination of experiments and simulations. The results of scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) all showed significant improvements in nucleation rates, film thickness, and grain size, particularly for grains with (111) orientation, when exposed to a 400 mT magnetic field during HFCVD compared to non-magnetic conditions. Magnetic field application in HFCVD was found to promote the formation of larger diamond grains and increase the film growth rate by nearly 45 %. Concurrent Finite Element Method simulations confirmed that the magnetic field improved reactive gas flow and temperature distribution across the substrate, which was consistent with experimental results. These findings suggest that magnetic field assistance in HFCVD may mitigate the limitations of bias assistance, such as the antenna effect, overheating, and stress imbalance. This approach is especially useful for substrates with complex geometries, such as the sharp edges of cutting tools, as it promotes even film growth.

Effect of CH4 concentration on the early growth stage of patterned diamond using high seeding density and hot filament chemical vapor deposition

Effect of CH4 concentration on the early growth stage of patterned diamond using high seeding density and hot filament chemical vapor deposition

Fabrication of Tungsten Oxide Nanowalls through HFCVD for Improved Electrochemical Detection of Methylamine.

In this study, well-defined tungsten oxide (WO3) nanowall (NW) thin films were synthesized via a controlled hot filament chemical vapor deposition (HFCVD) technique and applied for electrochemical detection of methylamine toxic substances. Herein, for the thin-film growth by HFCVD, the temperature of tungsten (W) wire was held constant at ~1450 °C and gasification was performed by heating of W wire using varied substrate temperatures ranging from 350 °C to 450 °C. At an optimized growth temperature of 400 °C, well-defined and extremely dense WO3 nanowall-like structures were developed on a Si substrate. Structural, crystallographic, and compositional characterizations confirmed that the deposited WO3 thin films possessed monoclinic crystal structures of high crystal quality. For electrochemical sensing applications, WO3 NW thin film was used as an electrode, and cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were measured with a wide concentration range of 20 μM~1 mM of methylamine. The fabricated electrochemical sensor achieved a sensitivity of ~183.65 μA mM-1 cm-2, a limit of detection (LOD) of ~20 μM and a quick response time of 10 s. Thus, the fabricated electrochemical sensor exhibited promising detection of methylamine with considerable stability and reproducibility.