Hot-filament Chemical Vapor Deposition Method Research Articles

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.

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.

The Effect of Boron Doping Concentration on the Electrochemical Oxidation of Chlorine Using BDD Electrode

Boron-doped diamond (BDD) electrode is an excellent candidate for anodic electrochemical oxidation of wastewater. However, higher concentrations of ClO3 − and ClO4 − of biotoxicity was found during chloride electrolysis using BDD electrodes compared to other electrode materials. In this study, BDD electrodes with five different boron doping concentrations were fabricated on silicon substrates using hot-filament chemical vapor deposition (HFCVD) method. The physical and electrochemical characterisation were conducted, which confirmed that with the decrease of boron concentration, the crystal size of the diamond decreased, oxygen evolution potential decreased, charge transfer resistance decreased while the electro-active surface area (EASA) increased. The electrochemical oxidation experiments of NaCl solution were carried out with these five BDD electrodes and time-dependent traces of product concentrations, current efficiencies and energy consumptions were compared and discussed. When the boron concentration increased, the minimum energy required to produce unit active chlorine (AC) decreased initially then increased, the same tendency was found in the yields of ClO3 − and ClO4 −. The lightly doped BDD (1.23 × 1020 cm−3) showed low energy consumption and high yield of AC, and low yields of ClO3 − and ClO4 −. Electrolysis of chlorine-containing organic wastewater was studied which further demonstrated the good performance of lightly doped BDD electrode.

Gas-jet HFCVD synthesis of diamonds from mixtures of hydrogen with ethylene and methane

The gas-jet deposition method (a modification of the Hot Filament Chemical Vapor Deposition method (HFCVD)) was used to deposit some diamond structures on a molybdenum substrate from a hydrogen-ethylene mixture activated on hot tungsten. The experiments were performed for two lengths of activation reactors at different ethylene flow rates. For comparison, some diamond structures were synthesized from a hydrogen-methane mixture under similar conditions. The resulting structures were studied with the scanning electron microscopy and Raman spectroscopy methods. The reacting mixture flow through the heated catalytic channel was simulated by solving the Navier-Stokes equations accounting for homogeneous and heterogeneous chemical reactions. The reactor (hot tungsten tube) length and diameter effects as well as carbonaceous admixture supply effects were analyzed. The main diamond precursor's formation pathways were analyzed and the reaction chains' complexity was demonstrated. The simulation results are in good agreement with the experimental data. The numerical experiments made it possible to reveal the growth process key driving parameters.

Study of deposition diamond to fill pores on cobalt removal surface adopting HFCVD method

While the presence of cobalt in conventional PCD tools had a detrimental effect on their cutting performance throughout the cutting process, cobalt removal PCD likewise had the issue of poor performance improvement. To address the issue of PCD's poor cutting performance, the pores remaining on the PCD surface after cobalt removal were filled using hot filament chemical vapor deposition (HFCVD). This relatively simple and effective approach was estimated to increase the cutting performance of PCD tools. For deposition, the carbon concentration was limited to 1%, 2%, 3%, 4%, and 5%, denoted by the numbers 1#, 2#, 3#, 4#, and 5#, respectively. SEM was used to observe the surficial and cross-sectional morphologies of the deposited PCD. The porosity of the deposited PCD surface was quantified using ImageJ software. X-ray diffraction and Raman spectroscopy were used to evaluate the diamond particle size and purity. The abrasion rate of the samples was determined using an abrasive rate tester. The flank wear of tools was then determined using a digital microscope, and the abrasion morphologies of tools were studied using an optical microscope following cutting. The results suggest that when the carbon concentration increases, the pores filling effect becomes superior and eventually inferior. The surface porosity of 2# is only 6.52%, which reaches the minimum, and that means 2# possesses the best pore filling effect. At the same time, 2# diamond grain size is the smallest, with relatively good purity and the smallest internal stress. When morphology and flank wear measures of cutting tools are compared, the tool life of 2# is almost double that of a general PCD tool. Thus, maintaining a carbon concentration of about 2% efficiently fills the pores of cobalt removal PCD, significantly improving the wear resistance and durability of the tools. In general, this study used HFCVD to deposit diamond to fill pores on the cobalt removal surface of the PCD tools. It was found that maintaining not too high carbon concentration can enhance the quality of diamond and filling ration, therefore improving the wearing performance of PCD tools. This experiment attempted to demonstrate the concept of utilizing diamond as a dense cover layer to deposit diamond grains into PCD tool pores. Then, carbon concentration was included as a significant factor in the deposition process in order to investigate the propensity of diamond pore nucleation and growth in order to fill the pores on the surface with the greatest possible quality. Finally, when the results of pore filling were compared to the results of real cutting, it was found that the cutting performance of PCD tools with improved filling was superior to that of conventional PCD tools.

Single-Crystal Diamond Needle Fabrication Using Hot-Filament Chemical Vapor Deposition.

Single-crystal diamonds in the form of micrometer-scale pyramids were produced using a combination of hot-filament (HF) chemical vapor deposition (CVD) and thermal oxidation processes. The diamond pyramids were compared here with similar ones that were manufactured using plasma-enhanced (PE) CVD. The similarities revealed in the morphology, Raman, and photoluminescent characteristics of the needles obtained using the hot-filament and plasma-enhanced CVD are discussed in connection with the diamond film growth mechanism. This work demonstrated that the HF CVD method has convincing potential for the fabrication of single-crystal diamond needles in the form of regularly shaped pyramids on a large surface area, even on non-conducting substrates. The experimental results demonstrated the ability for the mass production of the single-crystal needle-like diamonds, which is important for their practical application.

Characterization of Micro-Crystalline Diamond Tools Synthesized by HFCVD Process with Different Seeding Powders

Synthesis of diamond films on carbide insert is a recent area of research in surface engineering. This research is carryout to know the effect of different seeding powders on diamond coating of WC tool by Hot Filament Chemical Vapor Deposition (HFCVD) method. Here, the formation of microcrystalline diamond (MCD) on SPUN tungsten carbide (WC-Co) cutting tool insert is carried out. Basically, before coating in HFCVD method, the substrate cobalt content should minimize by ultra-sonic etching. The uncoated tools are seeded ultrasonically by Diamond, Iridium, Platinum and Tungsten powder at the same coating condition to observe the growth of diamond crystals. X- ray diffraction gives clear results of diamond plane and adhesion of coating. The purity of diamond crystal after coating can be clear by observing the Raman shift in Raman spectroscopy (RS). The tool is seeded with diamond powder gives more nucleation density due to the presence of more sp3 bond as compared with sp2. Use of diamond and platinum powder as a seeding material gives fully developed crystal and uniform coating during diamond film deposition by HFCVD technique, rather in case of other powder coating the discrete crystals were formed.

Influence of substrate bias on performance of diamond coating on WC cutting inserts for machining of aluminium by HFCVD process

The most important factors during deposition on different carbide base cutting tool inserts by using hot filament chemical vapour deposition (HFCVD) method are nucleation and growth of diamond. The negative dc biasing is the most outstanding technique in HFCVD method for improving the nucleation on the substrate surface. In the present investigation, the main objective is to analyse the influence of bias voltage on the WC substrate for nucleation, growth, adhesion and quality of diamond coating along with evaluation of machining performance in dry environment. Finally it has been confirmed that higher nucleation density including good quality diamond coatings along with reduced cutting force and better work surface finish were achieved under a definite reaction pressure with negative substrate bias.

Comparative investigations of the selective Co etching from hardmetal support layer of diamond coating

Selective cobalt etching from WC–Co composite usually carry out prior diamond deposition was investigated. Diluted Caro’s acid as primarily utilized etching reagent was used. The cobalt and tungsten dissolution from hardmetals (HM) were determined as a function of time and a comparison were done in case of different grade hardmetals. For comparison beside the hardmetals the pure metallic cobalt and binderless, plasma sprayed tungsten carbide dissolution also has been tested. Hot filament chemical vapor deposition (HFCVD) technic was used to investigate the diamond nucleation on the differently pre-treated samples. The investigation highlighted for that: a) the selective cobalt etching can due to the different rate of dissolution of the two components, however the dissolution of the WC was not zero, b) the dissolution rate governed by the composite substance structure by the pore size which has formed during the selective dissolution process, therefore the dissolution rate of both components was found to be influenced by the grain size of WC and the cobalt content of the hardmetal. c) The removed cobalt quantity from the hardmetal surface has strong effect on the diamond nucleation during HFCVD method. Based on this research a better understanding of the mechanism of the pre-treatment and a chance for optimizing the selective cobalt etching from hardmetals prior diamond deposition will be achieved.

Diamond Thin Film Coating on WC Substrate by HFCVD Method using Different Seeding Powders and Its Characterization

The formation of diamond thin solid film is studied by Hot Filament Chemical Vapor Deposition (HFCVD) by using different seeding powders on WC substrate. Here, we have deposited microcrystalline diamond (MCD) on SPUN cemented carbide (WC-Co) cutting tool insert using conventional HFCVD technique. The substrates were ultrasonically seeded with titanium, tungsten, molybdenum, diamond, combined diamond and tungsten powder at the same operation parameters to observe the difference in the growth of diamond by different seeding. Nucleation of diamond coating was studied after 40 minutes of coating with seeded substrate. The physical characteristics were studied by X-ray Diffraction (XRD).The Scanning Electron Microscope (SEM) was used to study the surface morphology. The diamond purity was studied with the help of Raman spectroscopy (RS). Reduction of cobalt percentage before and after pretreatment was studied by Energy Dispersive Spectroscopy (EDS). A very dense and uniform coating was deposited on the diamond powder seeded substrate. The nucleation density was found to be highest in diamond powder when compared with molybdenum and tungsten powder individually, because in initial stage the deposited material contains more sp2 content as compared to sp3 content. By using diamond and tungsten mixed powder the coating was uniform rather in case of only tungsten powder coating the discrete crystals were formed.

Effect of deposition pressure on the properties of amorphous carbon films by hot-filament chemical vapor deposition

Deposition pressure is an important factor for the preparation of amorphous carbon (a-C) films through vacuum method. However, researches about the properties, especially optical and electrical properties of a-C films influenced by deposition pressure are still rare. In this work, hot-filament chemical vapor deposition (HFCVD) was used to deposit conductive a-C films under different deposition pressure conditions. As deposition pressure raised from 5 to 160 Pa, a structural transition from a-C to nanocrystalline graphite that led to the increase of cluster size, sp2 content and crystalline quality of a-C films was observed. The hybrid structure composed of amorphous and nanocrystalline phases was also revealed by high-resolution transmittance electron microscope. The mobility, transmittance and conductivity of films increased while the optical gap and carrier concentration decreased by elevating the deposition pressure. As a result, a-C films prepared at 160 Pa showed the best property with a roughness of 0.412 nm, a transmittance of 67%, an optical bandgap of 1.25 eV, a resistivity of 75 μΩ m and a mobility of 3.17 cm2 V−1 s−1, which is comparable to those prepared through other methods. The small roughness, good transmittance and low resistivity implied that high quality a-C films can be prepared through HFCVD method by adjusting the deposition pressure.

Boron-Doped Graphene Directly Grown on Boron-Doped Diamond for High-Voltage Aqueous Supercapacitors

Boron-doped graphene/boron-doped diamond (BG/BDD) is synthesized by an electron-assisted hot-filament chemical vapor deposition (EA-HFCVD) method. Boron atoms are effectively doped into the graphen...

Effect of sub‐layer temperature during HFCVD process on morphology and corrosion behavior of tungsten carbide coating

AbstractWC coating was deposited on the polished and cleaned 316L stainless steel by Hot Filament Chemical Vapor Deposition (HFCVD) technique at 400°C and 500°C. Field Emission Gun Scanning Electron Microscope (FEG‐SEM) was used to study the corrosion morphology of the WC coatings. Energy dispersive spectroscopy (EDS) was used to analyze the chemical composition of the coatings. Coating porosity was measured by immersion in water. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of the coating in the solution of 1 mol/L H2SO4. Results showed that the WC coatings have a honeycomb microstructure where its porosity was increased at higher temperature of the sub‐layer. Also, the WC coating significantly increases the corrosion resistance of 316L stainless steel. And increasing the sub‐layer temperature in the HFCVD method reduces the corrosion resistance of the WC coating. Corrosion morphology was indicative of pitting corrosion of the WC coating.

Fast growth of conductive amorphous carbon films by HFCVD with filament temperature control

Amorphous carbon (a-C) films were synthesized on quartz substrates through a hot-filament chemical vapor deposition (HFCVD) method. Effect of filament temperature on the thickness, structural, morphological and electrical properties of a-C films was investigated. Both the crystalline quality and sp2 content of a-C films increased by raising the filament temperature from 1800 °C to 2000 °C. Sharp increase of the surface roughness was observed as the filament temperature increased from 2000 °C to 2100 °C. The a-C films deposited at the filament temperature of 2000 °C with a high growth rate of 35 nm/min exhibited the optimal quality with a small roughness of 0.546 nm and a low resistivity of 1.67 × 10−2 Ω·cm. These results indicated that HFCVD is a good method to prepare conductive a-C films rapidly and effectively.

THE ABRASION RESISTANCE AND ADHESION OF HFCVD BORON AND SILICON-DOPED DIAMOND FILMS ON WC–Co DRAWING DIES

Diamond films have been deposited on the interior hole surface of cobalt-cemented tungsten carbide (WC–Co) drawing dies from acetone, trimethyl borate (C3H9BO3), tetraethoxysilane (C8H[Formula: see text]O4Si, TEOS) and hydrogen mixture by hot-filament chemical vapor deposition (HFCVD) method. The structures and quality of as-deposited diamond films are characterized with field-emission scanning electron microscopy (FESEM) and Raman spectroscopy. The abrasion ratio and the adhesive strength of as-deposited diamond films are evaluated by copper wire drawing tests and ultrasonic lapping tests, respectively. The results suggest that diamond films with small grain size and high growth rate can be obtained due to the mutual effects of boron and silicon impurities in the gas phases. The results of ultrasonic lapping tests show that diamond films doped with boron and/or silicon can bear the severe erosion of the large diamond powder. Diamond films peeling off within the reduction zone of the drawing dies cannot be observed after testing of 2[Formula: see text]h. The abrasion ratio of boron and silicon-added diamond films is five times that of diamond films without any addition. Adding boron and/or silicon in the diamond films is proved to be an efficient way to obtain high-adhesive-strength and high-abrasion-resistance diamond-coated drawing dies.

The Effect of Deposition Parameters on the Growth Rate of Microcrystalline Diamond Powders Synthesized by HFCVD Method

Conventional diamond powders (<10 μm) are generally produced from crushing large-sized diamonds synthesized by high-pressure and high-temperature (HPHT) technique, whereas they have many morphological imperfections. In the present work, these powders are served as diamond seeds and regrown by hot filament chemical vapor deposition (HFCVD). Deposition parameters—such as the carbon concentration, substrate temperature, and bias current—which play a determined role in the homoepitaxial growth rate of micron diamonds, are investigated in their respective usual ranges. As shown in the experimental results, under the preconditions of maintaining the good morphology of crystals and inhibiting polycrystal growth, the growth rate of isolated diamond crystals can be controlled at 0.9 μm/h. Besides, the final improved powders have a wide range of particle sizes, which could fail to meet the requirements for commercial powders without the post-process of sieving.

Controlled growth of high-quality graphene using hot-filament chemical vapor deposition

High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm x 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, microRaman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I-2D/I-G ratio = 2 confirmed the presence of the monolayer graphene and the absence of `D' peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene.

Synthesis and investigation of silicon carbide nanowires by HFCVD method

Silicon carbide (SiC) nanowire has been fabricated by hot filament chemical vapour deposition (HFCVD) mechanism in the temperature range of 600–800°C. Synthesis is performed under vacuum in the atmospheres of hexamethyldisiloxane/alcohol (HMDSO/C2H5OH) vapour and hydrogen (H2) gas mixture. In this research dependence of SiC properties on temperature is discussed. Morphology and structural properties of SiC nanowire grown on glass substrate were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy diffraction spectrometer (EDX), and four-point probe (4PP). Also Mountains Map Premium (64-bit version) software is used to investigate morphological features of samples. In this context, the analysis of the motifs, depth histograms, statistical parameters, texture direction, fractal, and the peak count histograms of the nanostructure surface of samples are carried out. According to analysis, SiC films had a good crystal quality without defects or low residual stress. We found that increasing substrate temperature increases silicon and oxygen doping amount. We also found that electrical resistivity and surface roughness increased by increasing substrate temperature. This study showed that SiC nanowires with high density grew on the free catalyst glass substrate, and the alignment of SiC nanowires decreased.

Fractal features and surface micromorphology of diamond nanocrystals.

This paper analyses the three-dimensional (3-D) surface texture of growing diamond nanocrystals on Au thin films as catalyst on p-type Si substrate using hot filament chemical vapour deposition (HFCVD). Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), Raman, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were applied also to characterize the 3-D surface texture data in connection with the statistical, and fractal analyses. This type of 3-D morphology allows a deeper understanding of structure/property relationships and surface defects in prepared samples. Our results indicate a promising way for preparing high-quality diamond nanocrystals on Au thin films as catalyst on p-type Si substrate via HFCVD method.

The synthesis of size-controlled 3C-SiC nanoflakes and their photoluminescent properties

Size-controlled and high-purity 3C-SiC nanoflakes (NFs) are synthesized on the tips of vertically aligned carbon nanotube (VA-CNT) carpets with a hot-filament chemical vapor deposition (HF-CVD) method. The average diameter and height of SiC NFs can be tuned by changing the thickness of per-deposited Si and growth conditions. The growth process of the SiC NFs is suggested to be dominated by a vapor–solid (VS) mechanism. The prepared SiC NFs exhibit quantum-confinement effects, emitting strong violet-blue photoluminescence (PL) under ultraviolet excitation. The PL peak position changes from 410 to 416 nm as the excitation line increases from 290 to 400 nm. This result opens the possibility for the application of the luminescent solid-state freestanding 3C-SiC NFs in photonics as well as photonics/electronics integration.