Hot-filament Chemical Vapor Deposition System 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.

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.

Nitrogen-doping effect on single-crystal diamond synthesis by HFCVD

Nitrogen-doped homoepitaxial single-crystal diamond (SCD) films were grown on an SCD substrate by hot filament chemical vapor deposition (HFCVD) to confirm the potential that can yield high-quality single-crystal diamonds. The SCD films doped with 50 sccm nitrogen, grown by HFCVD, showed excellent surface properties based on optical microscopy, with a growth rate of 3.4 [Formula: see text]m/h, and a Raman peak around 1332 cm[Formula: see text] with a full width at maximum (FWHM) of 5.8 cm[Formula: see text], indicating high crystallinity. The FWHM of the (004) peak in the rocking curve was 392 arcsec for the nitrogen-doped SCD film, and that of the SCD substrate was 489 arcsec. Therefore, the crystalline properties and growth rates of the SCD films grown in the HFCVD system were improved, and the effect of nitrogen doping was verified.

Nanostructured boron-doped diamond electrode for degradation of the simulation wastewater of phenol

The applications of a boron-doped diamond (BDD) used in electrode application for toxic and refractory organic degradation have attracted much attention, and its efficiency is considered to be an important factor for its practical application. In this study, BDD thin films were prepared on Ti plates by double bias-assisted hot filament chemical vapor deposition (HFCVD) technique. A reactive ion etching process was introduced by a positive grid bias and a negative substrate bias which can generate an electric field in HFCVD system. Then a novel structure of BDD electrode with nanocone arrays was successfully etched from a flat diamond thin film by this system. The addition of the bias greatly improved the etching efficiency and promoted the formation of nanocones structures. The cyclic voltammograms (CV) test showed nanostructured BDD (NBDD) electrodes had excellent electrochemical performance almost the same as that of the electrodes with untreated surfaces. It had a large effective electroactive surface area (EASA), which was 31.0% greater than the unetched electrode. As a result, the NBDD electrode exhibited improved electrocatalytic performance as compared with the untreated one, i.e., an about 24.3% increase of chemical oxygen demand (COD) removal efficiency. Among them, the superiority of NBDD electrode was obvious in the initial stage due to its highest concentration in the initial stage. In addition, the NBDD electrode achieved higher average current efficiency (ACE) as compared with the untreated one.

Effect of magnetic and electric coupling fields on micro- and nano- structure of carbon films in the CVD diamond process and their electron field emission property

In this paper, both electric field and magnetic field were used to assist the hot filament chemical vapor deposition (HFCVD) and we systematically investigated the effects of which on the (1) phase composition, (2) grain size, (3) thickness and (4) preferred orientation of diamond films through SEM, Raman and XRD. The application of magnetic field in electric field, so called ‘the magnetic and electric coupling fields’, enhanced the graphitization and refinement of diamond crystals, slowed down the decrease of film thickness along with the increase of bias current, and suppressed diamond (100) orientation. During the deposition process, the electric field provided additional energy to HFCVD system and generated large number of energetic particles which might annihilate at the substrate and lose kinetic energy, while the Lorentz force, provided by magnetic field, could constrict charged particles (including electrons) to do spiral movement, which prolonged their moving path and life, thus the system energy increased. With the graphitization of diamond films intensified, the preferred orientation of diamond films completely evolved from (110) to (100), until the orientation and diamond phase disappeared, which can be attributed to (I) the distribution and concentration ratio of carbon precursors (C2H2 and CH3) and (II) graphitization sequence of diamond crystal facets. Since the electron field emission property of carbon film is sensitive to the phase composition, thickness and preferred orientation, nano- carbon cones, prepared by the negative bias current of 20 mA and magnetic field strength of 80 Gauss, exhibited the lowest turn-on field of 6.1 V −1 μm−1.

Plasma-enhanced synthesis of carbon nanocone arrays by magnetic and electric fields coupling HFCVD

In this paper, magnetic and electric fields coupling hot filament chemical vapor deposition (HFCVD) was used to fabricate a series of carbon films varying from nanocrystalline diamonds (NCD) to carbon nanocone arrays. The surface morphology and composition of the film were examined by scanning electron microscopy and Raman spectroscopy. After adding magnetic field, the morphology of the as-grown NCD film was a serried form instead of a rugged topography obtained under the absence of magnetic field. As electric field intensity increased, the etching degree of NCD films enhanced and the structural transformation of NCD to microcrystalline graphite occurred. We proposed that magnetic and electric fields can effectively introduce plasma into HFCVD system to optimize the film deposition process and studied the impact of magnetic and electric fields. The presence of electric field promoted ionization of reactive gas, and magnetic field made these ionic gases bound to a certain area around the sample, increasing the regional density of plasma. Specially, unique carbon nanocone arrays were obtained by synergistic effect of magnetic and electric fields, which exhibited optimal electron field emission properties, showing the lowest turn-on field of 5.65V/μm.

Raman and Photoluminescence Spectroscopy of Nanocrystalline Diamond Films Grown by Hot Filament CVD

Nanocrystalline diamond films were grown by hot filament chemical vapour deposition (HFCVD) in a mixture of methane and hydrogen gases. Three straight parallel wires filament configuration were used in the HFCVD system for the deposition of the films studied in this work. The deposition pressure for the growth of diamond films in this hot filament chemical vapour deposition (HFCVD) reactor have been optimized to be at 20 torr with the methane and hydrogen flow-rates fixed at 2 and 200 sccm respectively. The films studied in this work were grown at low deposition pressures of 2 and 5 torr using the same gas flow-rates used for the optimized diamond film growth including an additional film grown at pressure of 5 mbar with the methane flow-rate reduced to 1 sccm. The morphology showed the formation of closed packed diamond grains for the film grown at 5 torr with methane and hydrogen flow-rates fixed at 2 and 200 sccm. Decrease in pressure and methane flow-rate produced significant changes to the morphology of the diamond grains formed. X-ray diffraction showed that diamond phase phases were dominant in the films deposited at higher pressure. Raman and photoluminescence (PL) spectral analysis were performed using spectra acquired at 325 and 514 nm excitation energies. Raman analysis revealed that increase in deposition pressure from 2 to 5 Torr resulted in the transformation of the film structure from diamond-like-carbon to nanocrystalline diamond structure. UV excitation produced high PL emission intensity at 2.1 eV and the PL intensity was highest for the films deposited at the lowest pressure. Visible excitation on the other hand produced low intensity broad PL emission for all the films between 1.2 and 2.5 eV and the PL intensity was high for the films deposited at the highest deposition pressure.

The valuable role of renucleation rate in ultrananocrystalline diamond growth

This is a comprehensive study of the ultrananocrystalline diamond renucleation rate. The films deposited in a hot-filament chemical vapor deposition system (HFCVD) used an argon rich environment (90vol.%), known as ideal for ultrananocrystalline diamond deposition. Substrate temperature (750°C), total pressure (30Torr) argon flow rate (180sccm) were constant in all experiments. Methane concentrations of 0.25, 0.5, 1, 1.5 and 2vol.% balanced with hydrogen to a total flow rate of 20sccm. Scanning electron microscopy (SEM) let morphology inspection. Visible-Raman scattering leaded to estimating relative influence of sp2 bonds. X-ray photoelectron spectroscopy (XPS) measured the chemical bonds distribution. X-ray diffraction assessed crystallinity and diamond renucleation rates. The increase in methane content in the gas mixture promotes morphology changes from micro (faceted), to nano (cauliflower), and to ultrananocrystalline (ballas-like) diamond. It reaches a lamellar graphitic structure at the higher methane concentration. This transition is concurrent with: a decrease of film specific mass, an increase of diamond renucleation rate, an increase of sp2 phase content, as seen by Raman spectroscopy and, an increase of C–H bond associated with C–C bond, as measured by x-ray photoelectron spectroscopy. Renucleation shows up as a very important process that presents a quadratic correlation with [CH4] in the feed gas. This new result may help bridging MCD, NCD and UNCD into a single understanding of diamond growth.

Room-temperature photoluminescence from nitrogenated carbon nanotips grown by plasma-enhanced hot filament chemical vapor deposition

Nitrogenated carbon nanotips with a low atomic concentration of nitrogen have been synthesized by using a custom-designed plasma-enhanced hot-filament plasma chemical vapor deposition system. The properties (including morphology, structure, composition, photoluminescence, etc.) of the synthesized nitrogenated carbon nanotips are investigated using advanced characterization tools. The room-temperature photoluminescence measurements show that the nitrogenated carbon nanotips can generate two distinct broad emissions located at ∼405 and ∼507 nm, respectively. Through the detailed analysis, it is shown that these two emission bands are attributed to the transition between the lone pair valence and σ* bands, which are related to the sp3 and sp2 C–N bonds, respectively. These results are highly relevant to advanced applications of nitrogenated carbon nanotips in light emitting optoelectronic devices.

Influence of process parameters on growth of diamond crystal on cemented carbide substrates by HFCVD system

The synthesis of diamond at low pressure using Hot Filament Chemical Vapor Deposition (HFCVD) method has received significant attention in recent years for the unique characteristics of diamond. Among various input parameters, chamber pressure plays an important role in controlling nucleation, growth and morphology of coating. In this investigation, the morphology of diamond was analyzed after (1) pretreatment with acid, (2) pretreatment with acid and without diamond seeding and (3) pretreatment with acid and seeding. Keeping other input parameters constant the chamber pressure varied from low pressure (0.133kPa) to high pressure (6.666kPa). The variation of the crystal size with different input parameters were studied with Scanning Electron Microscope (SEM) micrographs and Raman spectroscopy. It was observed that cobalt inhibited diamond growth on the received carbide insert. Pretreatment with acid without seeding has improved diamond morphology. The pretreatment with acid and diamond powder seeding has improved diamond coating significantly.

Comparative Study of Nanocrystalline Diamond Deposition on WC–Ni and WC–Co Substrates

Tungsten carbide alloys possess a large number of applications, due to its high hardness, high resistance to heat and to wear, which makes it ideal to be used in wear parts of machinery or on surfaces liable to corrosion, abrasion or high temperatures. For practical applications, it is alloyed with cobalt (Co) or nickel (Ni) in order to improve its properties. The increasing demand of broadening the operation limits of some components, impose the need to improve its life time. Coating these parts with hard and smooth diamond thin film may improve the wear performance and decrease their roughness and friction coefficient. In this work, a comparative study of nanodiamond films deposit onto WC-Co and WC-Ni, by means of a hot-filament Chemical Vapour Deposition (HFCVD) system, is presented. The study was accomplished by varying the CH4/H2/Ar gas ratio of the deposition process. The substrate temperature was kept low (< 700 degrees C) to minimize the thermal stress in the coating-substrate system. The microstructure of the deposited diamond film was characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy and X-ray diffraction spectroscopy. Roughness of the working surfaces were also accessed prior and after the depositions.

Surface morphology, growth rate and quality of diamond films synthesized in hot filament CVD system under various methane concentrations

Hot filament chemical vapor deposition (CVD) technique has been used to deposit diamond films on silicon substrate. In the present study, diamond films were grown at various vol.% CH 4 in H 2 from 0.5% to 3.5%, at substrate temperature and pressure of 850 °C and 80 torr, respectively. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were employed to analyze the properties of deposited films. The formation of methyl radicals as a function of vol.% CH 4 not only changes film morphology but also increase film growth rate. At low, intermediate and high vol.% CH 4, cluster, faceted cubes and pyramidal features growth, were dominant. By increasing vol.% CH 4 from 0.5% to 3.5%, as the growth rate improved from ∼0.25 μm/h to ∼2.0 μm/h. Raman studies features revealed high purity diamond films at intermediate range of vol.% CH 4 and grain density increased by increasing CH 4 concentration. The present study represents experimentally surface morphology, growth rate and quality of diamond films grown in hot filament CVD system at various CH 4 concentrations.

Influence of periodic magnetic field on the growth of CVD diamond films at lower temperature

A periodic magnetic field (PMF) of B= B 0 sin ωt, where B 0=106 Guass and ω=40,000 rpm, was designed and first applied in a special hot-filament chemical vapor deposition (HFCVD) system for diamond synthesis. Different to the conventional HFCVD, an external PMF was introduced for diamond thin film deposition on a Si (1 1 1) substrate. The morphology and cross-section of the film were analyzed by field emission scanning electron microscopy (FESEM) while the bond structure was investigated using Raman spectroscopy. Compared with the conventional HFCVD, the growth rate of diamond film defined as the ratio of film thickness vs deposition time increases by about 7 times at 520 °C with PMF. The I Dia/ I G ratio in Raman spectra indicates that the quality of the diamond film grown with PMF is much higher than that of the film grown by conventional HFCVD. The research shows that the novel technology using PMF may have great practical application potentiality in CVD diamond growth at low temperature and in some relevant fields.

Local electrical properties of hydrogenated (001) and (111) surfaces of single crystalline diamond

The hydrogenation of Ib-type single crystalline diamond with grain size of several tens of micrometers, synthesized by high-pressure and high-temperature (HPHT) sintering, was carried out by hydrogen plasma treatment in a hot-filament chemical vapor deposition (HFCVD) system. After exposure to air, the surface conductivity of (001) and (111) facets of HPHT single crystalline diamond was measured. The influences of hydrogenation duration, temperature and gas pressure on the surface conductivity of (001) and (111) facets have been investigated. The measurement results show that the variation of hydrogenation conditions has a noticeable effect on the surface conductivity of single crystalline diamond, which is closely related to the formation of a chemical vapor deposition (CVD) regrowth layer on the facets induced by hydrogen plasma treatment process. In addition, (001) surface exhibits higher electrical conductivity than (111) surface, which is mainly attributed to less nitrogen concentration on the (001) surface than on the (111) surface.

Selective Growth of Vertically Aligned Carbon Nanotubes by Double Plasma Chemical Vapour Deposition Technique

The selective growth of vertically aligned carbon nanotubes (VACNTs) on large area copper substrates was carried out using a double plasma hot-filament chemical vapour deposition system. Three independent power supplies were used to produce two glow discharges within the vacuum reactor. The generation of two glow discharges and the efficient utilization of the electric fields, by controlling the key process parameters, enabled the production of VACNTs. Morphology, density and structure of carbon nanotubes were characterized using Scanning Electron Microscopy and Raman Spectroscopy.

Highly (111)-textured diamond film growth with high nucleation density

In a traditional hot-filament chemical vapor deposition (HF-CVD) system, highly (111)-textured diamond film was deposited on Si (111) substrate treated by diamond powder ultrasonic scratching or other methods. The relationship between the (111)-textured diamond film growth and the nucleation density has been discussed. The morphologies and structures of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy.

Chemical gases sensing properties of diamond nanocone arrays formed by plasma etching

A uniform diamond nanocone array was formed by plasma etching of diamond film in a hot filament chemical vapor deposition (HFCVD) system. A surface amorphous carbon coating layer, which is formed during CH4/H2 plasma-etching process, was removed by Ar plasma in a reactive ion etching system. The hydrogenation of diamond nanocones was performed in H2 ambience by using the same HFCVD system. The air-diluted NH3 and NO2 gases sensing properties of the diamond cone arrays had been studied by using electric current versus measurement time characteristics at room temperature. The repeatable chemical sensing properties of the hydrogenated diamond cone array sensor are enhanced, in comparison with as-formed diamond film. Surface two-dimensional hole gas structure and greatly increased surface-to-volume ratio both play a key role for the excellent detection performance. As-formed diamond nanocone arrays show a promising prospect for applications as chemical sensor for both reducing (NH3) and oxidizing (NO2) gases.

Synthesis of unstrained failure-resistant nanocrystalline diamond films

Nanocrystalline diamond films are highly strained materials, in general. This situation precludes from taking advantage of the many superlative properties of diamond that make it suitable for protective and tribological coatings (i.e. chemical inertness, hardness). Unstrained failure-resistant nanocrystalline diamond films were obtained by performing bias-enhanced nucleation in a microwave chemical vapor deposition system followed by nanocrystalline diamond deposition in a hot-filament chemical vapor deposition system. Thermal-shock tests showed that the bias-seeded films return to their initial unstrained state after differentially contracting and expanding, unlike nanocrystalline diamond films deposited on standard abrasion-seeded substrates, which undergo substantial stress changes that indicate the rupture of interfacial bonds. These results are discussed in terms of the nanocomposite interfacial structure induced by bias-seeding that enhances the nanocrystalline diamond film's tolerance to failure.

Fabrication of diamond tubes in bias-enhanced hot-filament chemical vapor deposition system

Deposition of diamond thin films on tungsten wire substrate with the gas mixture of ace- tone and hydrogen by using bias-enhanced hot filament chemical vapor deposition(CVD)with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are ob- tained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope(SEM)and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H_2O_2 and NH_4 OH.There is no residual stress in diamond tube after substrate removal.

Optical and structural properties of Diamond/GaN films

We report on the successful deposition of continuous boron-doped diamond films on p-GaN substrate in a hot-filament chemical vapor deposition (HFCVD) system. The Raman spectrum observed at 1331 cm − 1 is a distinctive, asymmetric Fano line shape, which shows that the films under the present growth condition are heavily doped. The photoluminescence spectra for GaN (the diamond is taken away from the Diamond/GaN sample) are characterized by significant spectral peak located at 3.358 eV. After annealing at 700 °C, a sharp PL line located at 358 nm (3.468 eV) is then observed. Additionally, the zero phonon line is located at 3.27 eV. However, this line has a blueshift of 0.25 eV in comparison with PL spectra for p-type GaN:Mg. This blueshift, which may be accounted for a by large lattice relaxation is associated with the dissociation of C diffusion into GaN.