Filament Chemical Vapor Deposition Reactor Research Articles

Production and Characterization of BDD/Si Electrodes for Environmental Analysis

Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemical Vapor Deposition reactor (HFCVD) using CH4/H2 gas mixtures. A series of experiments varying the levels of boron doping from 5000 to 25000 ppm were performed. Morphological, structural and electrochemical studies were conducted whose aim was the understanding about the film properties. The morphological and structural characterizations of these materials were made by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The evaluation of the electrodes was performed using cyclic voltammetry. The electrochemical response showed the influence of boron content in the work potential window. The doped diamond films produced and characterized in this work are efficient as an electrode for environmental applications.

Cathodic and anodic pre-treated boron doped diamond with different sp2 content: Morphological, structural, and impedance spectroscopy characterizations

In this work, the influence of cathodic (Red) and anodic (Ox) pre-treatment on boron doped diamond (BDD) films grown with different sp2/sp3 ratios was systematically studied. The sp2/sp3 ratios were controlled by the addition of CH4 of 1,3,5 and 7sccm in the gas inlet during the growth process. The electrodes were treated in 0.5molL−1 H2SO4 at −3 and 3V vs Ag/AgCl, respectively, for 30min. The electrochemical response of BDD films was investigated using electrochemical impedance spectroscopy (EIS) and Mott–Schottky Plot (MSP) measurements. Four film sample sets were produced in a hot filament chemical vapor deposition reactor. During the growth process, an additional H2 line passing through a bubbler containing the B2O3 dissolved in methanol was used to carry the boron. The scanning electron microscopy morphology showed well faced films with a small decrease in their grain size as the CH4 concentration increased. The Raman spectra depicted a pronounced sp2 band, mainly for films with 5 and 7sccm of CH4. MSP showed a decrease in the acceptor concentration as the CH4 increased indicating the CH4 influence on the doping process for Red–BDD and Ox–BDD samples. Nonetheless, an apparent increase in the acceptor concentrations for both Ox–BDD samples was observed compared to that for Red–BDD samples, mainly attributed to the surface conductive layer (SCL) formation after this strong oxidation process. The EIS Nyquist plots for Red–BDD showed a capacitance increase for the films with higher sp2 content (5 and 7sccm). On the other hand, the Nyquist plots for Ox–BDD can be described as semicircles near the origin, at high frequencies, where their charge transfer resistance strongly varied with the sp2 increase in such films.

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.

Simulation of temperature and gas density field distribution in diamond films growth on silicon wafer by hot filament CVD

In the present study, the temperature and gas density field inside the hot filament chemical vapor deposition (HFCVD) reactor, which play a determinate role on the growth rate and quality of as-deposited diamond films, are simulated using the finite volume method, and the influence of the size and arrangement of filaments and inlets are investigated. Firstly, the correctness of the simulation model is verified by comparing the temperature data obtained from the simulation with that measured in an actual depositing process, and the results show that the error between them is less than 3%. Thereafter, the deposition parameters are optimized using this model as N(filament number)=6, r(filament radius)=0.4mm, D(filament separation)=16–18mm, H(substrate–filament distance)=8–9mm, and 25 inlets. Finally, diamond films are deposited on silicon (100) wafers using above parameters and the results of characterization by SEM and Raman spectrum exhibit that the deposited diamond films appear homogeneous surface with fine-faceted crystals.

The influence of working gas on CVD diamond quality

Abstract The effect of the working gas pressure and its composition on diamond quality and particles size was investigated. The diamond layers were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor. A methanol–hydrogen gas mixture was used as the precursor gas. The structure of these films was characterized by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Typically, the diamond's crystallite size decreased with increasing pressure and increasing with methanol concentration. Additionally the admixture of non-diamond (sp2-hybridized carbon) phase also increased with increasing both of deposition pressure and of methanol concentration. It was observed that the deposition pressure has a weaker influence on diamond quality than the methanol concentration.

Diamond/WC bilayer formation mechanism by hot-filament CVD

A method for the growth of Diamond/WC bilayers in a single process is presented with interest for the production of well adhered electrical contacts to diamond surfaces. This process uses a common hot filament chemical vapor deposition (HFCVD) reactor, with W filaments as the source for the deposition of the metallic layer, and H2 and CH4 gasses as the reactive species for the diamond growth. The method begins by vaporizing the filaments in vacuum for a few minutes, followed by the chemical vapor deposition of diamond. The results have shown that by varying the filament vaporization time and temperature it is possible to deposit on the Si substrate tungsten containing coatings of different thicknesses. The process starts by vaporization of naturally oxidized filaments and deposition on the substrate. Afterward, the tungsten oxide carburises to W2C and WC phases. The CVD growth of the diamond layers on these carbide layers is dependent on the CH4/H2 ratios, system pressure and substrate temperature. The seeding of the Si substrates with diamond powder before the CVD process, guarantees that diamond is nucleated inside the metallic carbide layer, anchoring the top nanocrystalline diamond layer.

Hydrogen effect on the morphology and structure of 3D porous titanium in the HFCVD-diamond growth environment

Abstract Titanium hydride was obtained from hydrogenation process on pure titanium (Ti) using a hot filament chemical vapor deposition reactor. The Ti samples were produced from powder metallurgy technique and present three-dimensional porosity. The experimental parameters of the hydrogenation process were controlled in a similar way as those for diamond growth. The pressure inside the reactor was kept at 6.6 kPa for a H 2 flow rate of 100 sccm and hydrogenation time of 1 hour. The distance from the filaments to the Ti surface was kept at 5 mm. Hydrogenation processes were carried out at different temperatures of 773, 873, 973 and 1073 K. The morphology of the titanium hydrides was studied by scanning electron microscopy. The images showed an increase in the roughness titanium surface as well as the formation of cracks due to the hydride titanium precipitation. The structure of these titanium hydrides was analyzed by X-ray diffraction, performed through θ –2 θ scans from 1 to 15° grazing incident angle. The results revealed that the temperature enhanced the titanium hydride concentration in the samples with a predominant precipitation of TiH phase for the four temperatures studied.

Detection of phenol at boron-doped nanocrystalline diamond electrodes

The phenol quantification using boron-doped nanocrystalline diamond (BDND) from electroanalytical technique of square wave voltammetry (SWV) is reported. BDND depositions were performed using Hot Filament Chemical Vapor Deposition reactor, where it was possible to grow films with statics substrate-holder (sample S1) or with spinning substrate-holder (sample S2). The variation of this growth parameter induced significant changes on the electrode properties. For example, the electrode S2 presented smoothness surface with low roughness in relation to that for electrode S1. Besides, Raman spectra showed different features for both electrodes that could be related to boron incorporation. Electrochemical measurements also presented differences between electrodes, showing the advantages of electrode S2, such as, rapid charge transfer, large electrochemical area and excellent phenol detection limit ∼0.1mgL−1. The phenol standard sample of 8.0mgL−1 was used to validate the application of this electrode as a nanosensor. Its concentration calculated from SWV using electrode S2 was 8.2±0.2mgL−1 while from Ion Chromatograph it was 7.9±0.1mgL−1. These results demonstrated the high potential of BDND electrodes for electroanalytical applications.

Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940–1980 °C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 μm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits.

Vapor–solid–solid Si nano-whiskers growth using pure hydrogen as the source gas

This paper describes the growth mechanism and structure of Si whiskers grown on a Si substrate in a tungsten hot filament chemical vapor deposition reactor with pure hydrogen as source gas using a two step process. In the first step, atomic hydrogen etched the silicon surface, forming silicon hydrides that react with tungsten from the filament. The resulting silicide particles deposited on the silicon surface forming a mesh-like pattern. The particles work as an etching mask against hydrogen radical etching of the silicon surface and inverted-pyramids or V-groove-shaped surface texture were obtained. In the second step the filament current was reduced and whiskers grew onto the substrate due to the interaction of the silicon hydrides with the particles and subsequent precipitation of saturated Si. The whiskers were found to have tungsten silicide particles on their tip, suggesting the whisker growth was through the Vapor–Solid–Solid (VSS) mechanism. A balance between the hydrogen radical etching effect and the supply of silicon hydride from the etching reaction on the silicon surface is crucial for the growth of dense silicon whiskers.

Improvements in CVD/CVI processes for optimizing nanocrystalline diamond growth into porous silicon

This paper reports a novel procedure to infiltrate nanocrystalline diamond films (NCD) on porous silicon (PS) substrate. The NCD/PS films resulted in a composite material, with great potential for electrochemical application, mainly due to its high active surface area. The Hot Filament Chemical Vapor Deposition reactor was changed to Hot Filament Chemical Vapor Infiltration reactor in order to grow NCD films infiltrated into deep holes of PS substrate. This procedure allowed the infiltration of the reacting gases into the porous structure where the nucleation takes place, followed by the coalescence and film formation at pore bottoms and walls. In this configuration an additional entrance of CH 4 was located next to the PS substrate using two distinct positions called “underneath” and “above”, with the use of the additional flow accurately underneath or above of the samples. In general, the combination of these two configurations with additional carbon sources provided NCD film infiltration in PS substrate with success with only 60 min of growing time. Particularly, the films obtained from the positions called “above” presented the best morphology, with high quality and crystallinity, confirmed from its scanning electron microscopy, Raman scattering spectroscopy and high resolution X-ray diffraction spectra, respectively.

The effect of tungsten coating on the properties of diamond thick films

According to the physical properties of pure tungsten and tantalum and their carbides, a layer of tungsten thin films coating three tantalum filaments at a current of 750 A was prepared by us for the first time and called tungsten coating. Diamond thick films were deposited in a hot filament chemical vapor deposition (HFCVD) reactor using tantalum filaments before and after tungsten coating, respectively. The success of tungsten coating is verified by scanning electron microscopy examination of these filaments. The remarkable discrepancies in thermal conductivity, colors of diamond thick films, and electron dispersion spectroscopy of the films substantiate the success of tungsten coating, too. The effects of tungsten coating on the quality of diamond films were finally evaluated by Raman spectra.

Controlled synthesis of diamond and carbon nanotubes on Ni-base alloy

A Ni-base alloy Inconel 600 has been used as substrate for growing two typical carbon thin film materials, diamond and carbon nanotubes (CNTs), in a hot filament chemical vapor deposition reactor with methane–hydrogen mixture. Under typical deposition conditions, the deposits formed on the as-polished alloy substrate comprise duplex layers, outer diamond layer and intermediate graphite layer. An Al thin film applied as an interlayer on the Inconel alloy effectively prevented the growth of intermediate graphite, and only a dense, adherent diamond film was deposited. When the substrate was negatively biased, a glow discharge was initiated and aligned carbon nanotubes were exclusively synthesized. No diamond was formed in this case.

Silicon Whisker Growth Using Hot Filament Reactor with Hydrogen as Source Gas

Si whisker growth on a silicon substrate, using only pure hydrogen gas flow in a hot filament chemical vapor deposition reactor, has been studied by scanning and transmission electron microscopy. At the initial stage of the growth, tungsten–silicide particles are formed due to hydrogen radical etching by the filament. Simultanously the Si substrate exhibits a surface texturing. After long residence times of hydrogen gas in the reactor, silicon whiskers, with diameters between 10 and 50 nm, were observed on the textured silicon surface. Each whisker has a silicide particle at its tip. A mechanism of silicon whiskers growth using this method with hydrogen gas is proposed.

Fabrication of a TiO2−BDD Heterojunction and its Application As a Photocatalyst for the Simultaneous Oxidation of an Azo Dye and Reduction of Cr(VI)

A TiO2-boron doped diamond (TiO2-BDD) heterojunction was employed as a photocatalyst to simultaneously oxidize an azo dye C.I. reactive yellow 15 (RY15) and reduce hexavalent chromium (Cr(VI)). This heterojunction was fabricated first by depositing a BDD film on a Ti sheet in a hot filament chemical vapor deposition reactor, followed by covering a layer of TiO2 in a metal-organic chemical vapor deposition system. The morphology of this heterojunction was characterized by using a scanning electron microscope (SEM). X-ray diffraction (XRD), Raman spectroscopy, and current-voltage (I-V) measurement were used to characterize its structures. Additionally, the characterization of surface photovoltage showed that the TiO2-BDD heterojunction exhibited a higher photovoltage response and a better ability for charge separation than the photocatalyst of TiO2 directly deposited on a Ti sheet (TiO2-Ti). The photocatalytic experiments revealed that the kinetic constants for the oxidation of RY15 and the reduction of Cr(VI) were, respectively, increased by 85 and 71% when the photocatalyst of TiO2-Ti was replaced by the TiO2-BDD heterojunction. Meanwhile, a significant synergy was confirmed in the simultaneous oxidation of RY15 and reduction of Cr(VI). The enhanced photocatalytic ability of the TiO2-BDD composite could be attributed to the heterojunction. The possible photocatalytic mechanism was also discussed.

Effect of Water Contained in Acetone on Nanocrystalline Diamond Particles or Film synthesis

This paper describes a series of experiments to grow nanocrystalline diamond (NCD) in a closed system hot filament chemical vapor deposition (HFCVD) reactor using acetone containing various amounts of water. A commercial acetone includes a slight amount of water, so we tried to dehydrate from the acetone. Next, diamond was synthesized under the various type of water content. We investigate about an optimum acetone/water concentration ratio in diamond particle formation and film formation. We clarified the effect of water concentration on the morphology, nucleation density and size. The morphology, and grain size and structure of the diamond were examined with field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. We will refer to the synthesis process in detail about diamond and NCD.

Investigation of conditions for preparation of oriented nanotubes at department of microelectronics in a modified plasma-enhanced hot filament chemical vapor deposition reactor

This paper describes the preparation of nanotubes on copper, iron and on silicon wafers with pre-deposited diffusion barrier and catalyst particles. Experimental results describe the influence of an additional electrode on the growth and orientation of the nanotubes in the hot filament chemical vapor deposition reactor. Implementation of an electrode in the Hot Filament Chemical Vapor Deposition reactor has a considerable influence on the conditions in the reactor and growth of oriented nanotubes. The effect of pressure on the orientation was observed.

Carbon spheres formed by hot filament chemical vapour deposition

We report the formation of carbon spheres on the surface of a tungsten filament used in a hot filament chemical vapour deposition reactor. The concentration of the gas precursors (methane diluted in hydrogen) was varied from 3.5 up to 5 vol.% and the total working pressure from 30 to 35 Torr. The reaction time was varied up to a maximum of 60 min. Analysis of the tungsten filament surface by scanning electron microscopy/energy dispersive X-ray analysis revealed smooth microspheres composed of carbon with diameters up to 25 μm. When increasing methane concentrations, pressure and reaction time, the number density of the spheres and their diameters increased. The mechanism of formation involves adsorption of hydrocarbon species onto the filament surface followed by the formation of tungsten carbide microspheres which act as nucleation centres for the growth of smooth carbon microspheres.

Synthesis and field electron emission characteristics of diamond multilayer films grown by graphite etching

Diamond multilayer film with nanocrystalline diamond film coated on a layer of diamond nanocone film, was synthesized on silicon substrates by using in situ graphite etching in a hot filament chemical vapour deposition reactor. Many small and sharp protrusions on the surface of the multilayer film were observed using scanning electron microscope and atomic force microscope. The multilayer film exhibits lower turn-on field and larger emission current than flat diamond films and diamond nanocone films. Field electron emission measurements at different residual gas pressures indicate that emission current of the multilayer film shows no obvious degradation and the Fowler–Nordheim (F–N) plots parallel to each other when the residual gas pressure is increased from 10−7 to 10−5 Torr. At a higher pressure of 10−3 Torr, obvious degradation of emission current was observed. The slope of the F–N plot becomes larger, indicating that the work function is increased. The possible reason is that the surface of the multilayer film is fully covered by residual gas molecules.

Dependence of diamond nucleation and growth through graphite etching at different temperatures

Diamond films have been grown on silicon substrate from graphite etching as a carbon source with atomic hydrogen instead of using conventional hydrocarbon in the feed gas. A graphite plate was used as sample support in a hot filament chemical vapor deposition reactor. Graphite temperature demonstrated to have a strong dependence with the diamond nucleation and growth rate. Scanning electron microscopy (SEM) images of graphite targets associated with their Raman spectra were used to analyze their graphite morphology and structural properties before and after etching process for each graphite temperature studied. The results showed that chemical erosion intrinsically induces graphite surface changes that influence Raman spectra. The disorder behavior from the I D/ I G ratio presented a maximum value at 900 °C, for 60 min of etching time, when compared with graphite surface at room temperature before atomic hydrogen etching. SEM diamond images were also used to analyze the nucleation rate. Diamonds grown during 15 min at 600 and 700 °C presented the higher nucleation rate. For growth time of 30 min the diamonds are continuous, covering the entire Si substrate surface, with submicrometer grain size. Raman spectra showed good quality diamond coating. Diamond content or diamond purity values, evaluated for growth time of 15, 30 and 60 min increases with the increase of the graphite temperature confirming the high carbon content in the first stage of diamond growth.