Filament Chemical Vapor Deposition Method Research Articles

Cutting Performances of Diamond Coated Milling Tools in Machining Aluminum Alloy

CVD diamond films are deposited on cobalt cemented tungsten carbide (WC-Co) endmills using hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM) and Raman spectroscopy are used to characterize the as-deposited diamond films. To evaluate the cutting performances of as-fabricated CVD diamond coated endmills, dry milling tests are conducted using aluminum alloy as the workpiece material. The uncoated WC-Co endmills are also adopted in the milling tests for the sake of comparability. The experimental results show that the build-up edge formed on the uncoated WC-Co endmills at very early stage of the cutting tests. Comparatively, CVD diamond coated endmills present an excellent anti-adhering property. The result suggests that depositing diamond coating on WC-Co endmills is a viable way to improve their cutting performances in machining of aluminum alloy materials

Studies on distribution of element contents in transient layer at interface between boron-doped diamond film electrode and tantalum substrate

The boron-doped diamond film (BDD) grown on tantalum (Ta) substrate as an electrode (BDD/Ta) was prepared by hot filament chemical vapor deposition method. The experimental results demonstrated that our BDD/Ta had high current efficiency, strong ability to degrade wastewater, good corrosion stability and long lifetime. These excellent characteristics of BDD/Ta have been explained in terms of Rutherford backscattering (RBS) experiments. RBS investigation revealed that the continuous transient layer at the interface between boron-doped diamond film and Ta-substrate was formed and the microstructure of the continuous transient layer given by the continuous distribution of all element contents at the interface was obtained. The thicknesses of boron-doped diamond film and the continuous transient layer were about equal to 8000 × 10 15 atoms/cm 2 and 5800 × 10 15 atoms/cm 2, respectively. The formation of the continuous transient layer at the interface can eliminate the mismatch of thermal expansion coefficients (TEC) at the interface and only lead to the slow change of TEC because of the continuous distribution of element contents of the film and substrate in the transient layer at the interface. Thus, there is no residual stress to concentrate on the interface and the stress-corrosion delamination of the film disappears. Therefore, the corrosion stability and lifetime of BDD/Ta increase and last well, that have been verified by X-ray diffraction (XRD) experiments.

Selective synthesis of diamond and CNT nanostructures directly on stainless steel substrates

Without surface pretreatment or applying additional interlayer, diamond films have been directly synthesized on an Fe–25Cr–5Al steel substrate by a hot filament chemical vapor deposition method from an H 2-1vol.% CH 4 gas mixture. Due to an effective removal of intermediate graphite phase from the diamond–steel interface, the coated diamond films were continuous and adherent well to the steel substrate. Aligned conical diamond structures were also achieved on this steel substrate by negatively biasing the substrate holder and inducing a glow discharge. The deposition behavior of carbon on Fe–Cr–Ni steel substrate was different. A graphite-rich carbon film incorporated with diamond particles grew in the absence of biasing, then aligned carbon nanotube bundles were formed in the presence of negative biasing and glow discharge. The different deposition behavior of carbon on the two kinds of steel substrates was addressed in terms of the effect of their chemical compositions.

Growth of Nano Crystalline Diamond on Silicon Substrate Using Different Etching Gases by HFCVD

We investigate the effects of etching gases on the synthesis of nano crystalline diamonds grown on silicon substrate at the substrate temperature of 550°C and the reaction pressure of 4 kPa by hot filament chemical vapor deposition method, in which CH4 and H2 act as a source and diluting gases, respectively. N2, H2, and NH3 were used as the etching gases, respectively. Results show that the optimum conditions can be obtained only for the case of H2 gas. The crystal morphology and crystallinity of the samples have been examined by scanning electron microscopy and X-ray diffraction, respectively.

Frictional Characteristics of Ultra–Thin Polytetrafluoroethylene (PTFE) Films Deposited by Hot Filament–Chemical Vapor Deposition (HFCVD)

Frictional characteristics of polytetrafluoroethylene (PTFE) films deposited by a hot filament chemical vapor deposition (HFCVD) method on glass substrates was investigated. A universal micro-tribotester (UMT) was used in the ball-on-flat configuration to examine the effect of coefficient of friction (COF). The effects of normal force (2.5–15 N), sliding speed (1.4 × 10−3 to 14 mm/s) and film thickness (0.3, 1, 5, 10 μm) on the frictional behavior of the PTFE film were tested. Optical microscopy was used to examine the wear tracks of the PTFE films. In addition, durability of the PTFE films was examined by monitoring the change of COF in ball-on-disk tests. The COF values of the tested PTFE films were found to be in the range 0.03–0.18 depending on the measurement conditions. In particular, PTFE exhibits a low COF at slow speeds and high normal forces compared to a high COF at high speeds and small normal forces. Modified Hertzian contact equations and finite element analysis were used to analyze the indentation process. Comparison with the width of the experimental wear tracks indicates that the PTFE layer has a small contribution in carrying the normal load yet provides good protection against tangential forces.

Properties of ZnO/Diamond Film Heterojunction

High quality boron-doped p-type freestanding diamond (FSD) films with smooth nucleation surface were prepared by hot filament chemical vapor deposition (HFCVD) method. The effects of B/C ratios on the electrical properties of FSD films were investigated by Hall effect measurement system. N-type Al-doped ZnO films were prepared on p-type FSD films by radio-frequency (RF) magnetron sputtering method to fabricate heterojunction. The I-V characteristic of the heterojunction was examined. The results showed a rectifying behavior of this structure.

Diamond film growth on the Mo–Re alloy foil

Nanocrystalline diamond film was deposited on the substrate of Mo–Re alloy foil by using a hot filament chemical vapor deposition (HFCVD) method. The morphology, band structures and crystalline structure of the film were analysed by scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The results show that the thickness of the diamond film is about 300 nm after 1 h deposition. There is a 2H-Mo 2C layer between the diamond film and the Mo–Re substrate. The values of a and the ratio c/ a of Mo 2C are 3.003 and 1.579 Å, respectively. This Mo 2C layer might be formed due to carbon atoms in the gas phase diffusing into the Mo–Re alloy.

Study on the Cutting Performance of HFCVD Diamond Coated Silicon Nitride Inserts in Dry Turning Aluminum Silicon Alloy

To evaluate the cutting performance of CVD diamond coated silicon nitride insert, two kinds of CVD diamond films, namely microcrystalline diamond (MCD) and composite diamond films, are deposited on silicon nitride (Si3N4) inserts using the hot filament chemical vapor deposition (HFCVD) method. The characterization of as-deposited diamond films is conducted using the scanning electron microscope (SEM), optical interferometric profiler, X –ray diffraction (XRD) and Raman spectrum. The turning tests for as-fabricated MCD and composite diamond coated insert, as well as uncoated silicon nitride insert, are performed in dry turning aluminum silicon alloy, where the cutting speed, feed rate and depth of cut are fixed as ν = 2000 r/min, f=0.1 mm/r and ap=1 mm. The results demonstrate that the main tool failure is the tool wear. As compared with the uncoated silicon nitride insert, the woking life time of the diamond coated insert can be increased by a factor of above 7.

Study of the synthesis of tungsten trioxide nanostructured arrays by tungsten hot filament chemical vapor deposition method and their field emission properties

Tungsten trioxides (WO3) nanorod arrays had been fabricated at different substrate temperatures by hot filament chemical vapor deposition. The morphology of the WO3 nanorod array is significantly dependent on the substrate temperature in a relatively narrow range (600–800 °C). Through the x-ray diffraction pattern, different preference growth directions of WO3 nanorods at different substrate temperatures were observed. A discussion of the possible growth mechanism is given. Furthermore, the substrate temperature during the growth was also found to be closely related with the morphologies of the nanorod arrays and their field emission properties.

Study on the Fabrication and Cutting Performance of HFCVD Diamond Coated Silicon Nitride Inserts

Microcrystalline diamond (MCD) and fine-grained diamond (FGD) films are deposited on silicon nitride (Si3N4) inserts using the hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM), X –ray diffraction (XRD) and Raman spectrum are employed to characterize these as-deposited diamond films. Cutting performance of as-fabricated CVD diamond coated Si3N4 inserts is examined in dry turning glass fiber reinforced plastics (GFRP) material, comparing with the uncoated Si3N4 inserts. The results indicate that the tool failure is mainly attributed to its severe flank wear, which is caused by continuous friction and impact brought by many hard SiO2 particles distributed in the GFPR work piece. The lifetime of Si3N4 inserts can be prolonged by depositing MCD or FGD films on them and the FGD coated insert shows better wear resistance than the MCD coated one.

Growth and characterization of diamond micro and nano crystals obtained using different methane concentration in argon-rich gas mixture

Diamond with different grain sizes and nanographite films were grown on silicon and diamond substrate using 90 vol.% argon in hydrogen and methane gas mixtures by hot filament chemical vapor deposition method (HFCVD). In current study, the methane volume concentration was varied from 0.125 to 2 vol. % in order to estimate its effect on film morphology. The substrate temperature was varied from 550 to 850 °C by external heating independently of other CVD parameters, in order to estimate the activation energy. Characterization techniques have involved Raman spectroscopy, high resolution X-ray difractometry and scanning electron microscopy. The CHEMKIN computer package has also been used to simulate the experiments. The results obtained here indicate a single mechanism for diamond growth but with a high competition with sp 2 phase's growth.

Carbon monoxide sensing at room temperature via electron donation in boron doped diamond films

Abstract We report room temperature detection of carbon monoxide (CO) below 100 parts per million in air using boron doped diamond films prepared by hot filament chemical vapor deposition method. Gas sensing characteristics are observed to be improved with larger grain size in the films. Sensing characteristics for 100 ppm CO with response time of 30 s and recovery times of ∼50 s at room temperature show the excellence of boron doped diamond as CO sensor material. The lowest values of response time ∼5 s and recovery time ∼20 s were observed for BDD with grain size of 1 μm for 1000 ppm of CO in air. The carbon monoxide sensing mechanism is attributed to electron donation to p-type boron doped diamond as a result of CO oxidation on its surface.

Hot filament CVD of Fe–Cr catalyst for thermal CVD carbon nanotube growth from liquid petroleum gas

A hot filament chemical vapor deposition (HFCVD) method was used to prepare Fe–Cr thin film on Si substrate. The produced layers were used as catalysts for growing carbon nanotubes (CNTs) from liquid petroleum gas (LPG) at 825 °C by thermal CVD (TCVD) method. To characterize the obtained catalysts or CNTs, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman spectroscopy were used. CNTs were grown on HFCVD derived Fe–Cr catalyst with the LPG as carbon source successfully. It was found that an annealing process on catalysts enhances the surface concentration of Cr atoms and reduces the sizes of catalyst particles. The grown CNTs on annealed sample were morphologically denser with smaller diameters compared to the as deposited one. In addition, the effect of filament temperature on CNTs was investigated. By increasing the filament temperature from 850 to 1050 °C the surface density and diameters of CNTs were improved.

Fabrication of Boron-Doped Diamond Nanorod Forest Electrodes and Their Application in Nonenzymatic Amperometric Glucose Biosensing

A boron-doped diamond nanorod forest (BDDNF) electrode has been fabricated by hot filament chemical vapor deposition (HFCVD) method. This BDDNF electrode exhibits very attractive electrochemical performance compared to conventional planar boron-doped diamond (BDD) electrodes, notably improved sensitivity and selectivity for biomolecule detection. The BDDNF electrode, with the possibility of fabricating a sensitive biosensor for glucose without any catalyst or mediators, shows good activity toward direct detection of glucose by simply putting the bare BDDNF electrode into the glucose solution. Furthermore, the marked selectivity of the BDDNF electrode is very favorable for the determination of glucose in the presence of ascorbic acid (AA) and uric acid (UA). The robust sensitive and selective responses of this nanostructure indicate the promise of this kind of diamond electrode for real applications.

Bias enhanced nucleation of diamond thin films in a modified HFCVD reactor

In this study we investigated the nucleation of synthetic diamond thin films on Si substrates by double bias enhanced Hot Filament Chemical Vapour Deposition (HFCVD) method. First, we investigated the influence of the bias voltage and secondly the influence of the nucleation time under different bias voltages. The bias voltage was varied from −120 V up to −220 V as well as the nucleation time was changed from 30 up to 120 min in order to obtain the optimized nucleation conditions for following growth of continuous diamond layer. Samples were analyzed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. SEM was used for determination of cluster sizes and their distribution on the Si surface, while Raman Spectroscopy for determination and analysis of carbon phases.

Effect of surface morphology on the frictional behaviour of hot filament chemical vapour deposition diamond films

A novel deposition method combining the conventional hot filament chemical vapour deposition method and the polishing technique is proposed for fabricating ultra-smooth composite diamond (USCD) films onto cobalt cemented tungsten carbide substrates. SEM and AFM investigations show that the deposited USCD films have ultra-smooth and uniform surface, and their surface roughness values are measured by using an AFM and a surface profilometer as Ra∼ 59 and ∼88.8 nm, respectively. The tribological properties of USCD films are examined in comparative friction tests with a microcrystalline diamond (MCD), fine-grained diamond, and polished MCD films, and the effect of surface morphology on the friction behaviour of diamond films is highlighted. Friction tests show that the polished MCD and USCD films exhibit very low friction coefficients of approximately 0.08, 0.12, and 0.17, while dry sliding against counterfaces of alumina ceramic, ball-bearing steel, and copper materials. Intensive interactions between two surfaces of the mating parts result in gradual blunting of the sharp tips of diamond crystallites and accumulation of wear debris on the worn surface of diamond films. Adhered wear debris on the diamond films are supposed to have a significant influence on their frictional behaviour because they will cause increasing adhesive strength between the mating surfaces, and thus a higher friction coefficient for the contact.

Metallic electrical transport in inter-graphitic planes of an individual tubular carbonnanocone

Tubular carbon cones (TCCs) with a herring-bone-like graphitic structure are synthesizedon gold wire via the bias-assisted hot filament chemical vapor deposition (HFCVD)method. The electrical transport properties of an individual TCC are studied in thetemperature range from 300 to 500 K by using a double probe scanning electronmicroscopy (DPSEM) in situ electrical measurement system. The high-resistanceI–V characteristics of W–TCC–Au back-to-back double junctions show that electrons tunnelthrough the W–TCC junction, while thermoionic transport through the Au–TCC junctioncontributes to low-resistance properties. Temperature dependence of the electricalcharacteristics indicates that inter-graphitic-plane electrical transport in TCC is metallic.

Experimental and Molecular Dynamics Investigation on Tribological Properties of Nanocrystalline Diamond Films

Nanocrystalline diamond films were deposited on cemented tungsten carbide substrates using hot filament chemical vapor deposition (HFCVD) method, and their tribological properties were investigated by friction experiments and classical molecular dynamics simulations. The friction tests were performed on a ball-on-plate type reciprocating friction tester under various normal loads and sliding velocities conditions; the experimental results suggested that the friction coefficient of diamond films showed increasing tendency with the growing normal load and sliding velocity. Furthermore, classical molecular dynamics simulations were conducted to investigate the changes in atomic scale friction behaviors of diamond films under extremely high normal load and sliding velocity conditions, the atomistic sliding mechanism was also discussed in this study.

Combined model for growing mechanism of carbon nanotubes using HFCVD: effect of temperature and molecule gas diffusion

Growth of a dense forest of vertically-aligned carbon-nanotubes (VA-CNTs) by a hot filament chemical vapor deposition (HFCVD) method was investigated. The growth of very pure VA-CNTs via the bottom growth mechanism was extremely fast during the initial few minutes, but it slowed down and reached the terminal height of a couple of millimeters. The different temporal variations of the VA-CNT height and growth rates corresponding to different growth stages indicated that a temperature-mediated thermodynamic model, precursor diffusion, and catalyst deactivation were responsible for the VA-CNT growth in respective stages.

Two-step growth of HFCVD diamond films over large areas

This paper reports the results of a two-step hot filament chemical vapor deposition method to improve the quality of diamond films. Diamond films were deposited on a Si(100) substrate having an area of 45 cm 2 and a thickness of 60 μm, employing a HFCVD system. The first step is the growth of CVD diamond in the HFCVD reactor. In the second step, the samples were treated in a saturated solution of H 2SO 4:CrO 3 and rinsed in a (1:1) solution of H 2O 2:NH 4OH. After this procedure, a second diamond layer was deposited. The diamond films were analyzed by Raman scattering spectroscopy (RSS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The films showed a high degree of purity with a thickness of 60 μm, presenting uniform characteristics over a large area.