Filament Chemical Vapor Deposition Reactor Research Articles

Customized boron-doped diamond electrodes for efficient water treatment via HF-CVD parameter optimization

Among the Design of Experiments (DoE) approaches available, the Taguchi method offers a methodical and effective way to optimize designs with fewer experimental trials. The effects of deposition conditions on the final properties of boron-doped diamond (BDD) films for water treatment applications deposited in a Hot Filament Chemical Vapor Deposition (HF-CVD) reactor were evaluated by applying a Taguchi Matrix. Methane to hydrogen (CH4/H2) ratio, argon mass flow, and total gas pressure were the controllable factors, each in three different levels. Diamond quality was affected by a combination of the three considered factors. A 0.02 CH4/H2 ratio was found as the optimal value to yield films with reduced non-diamond carbon inclusions in our CVD system. Resistivity, residual stress, double-layer capacitance, and surface roughness were mainly affected by total pressure and argon content. The methane content and the total pressure significantly influenced growth rate and grain size. The latter was primarily responsible for changes in the electrochemical potential window and the electron transfer process of the BDD films. Within the studied range of deposition conditions, the optimal deposition parameters to obtain BDD films for water treatment applications were: 0.02 CH4/H2 ratio, 25 mbar total gas pressure, and 30 sccm argon mass flow.

Utilization of catalytically active metals in mining waste and water for synthesis of carbon nanotubes

This study presents the application of fine-grained precipitates from mine waters for the synthesis of carbon nanotubes. Experimental synthesis of carbon nanotubes was carried out on natural substrates taken from the Slovak mining localities Markušovce, Smolník and Poproč. The substrates were obtained from mining waste taken from the shore dark sediment settling ponds in Markušovce, from the water flowing out of the mine in Smolník and from the sediment collected from the mine of Poproč. The main components of the colloidal residues resulting from the extraction of ores are particles containing catalytically active metals. Microscopic analysis of nanocomposites synthetized in a hot filament chemical vapour deposition reactor shows that the sediments from all residues after ore mining have a high ability to catalyse the synthesis of carbon nanotubes. The combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes. • Precipitates from mining waste and water were used for catalyst preparation. • Colloidal residues are particles containing catalytically active metals. • Catalytically active metals are used for synthesis of carbon nanotubes and for nanocomposite formation by CVD technique. • Combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes and nanofibers.

Mitigating residual stress of high temperature CVD diamond films on vanadium carbide coated steel

In this work, a process condition was created to deposit a thin film of diamond on AISI O1 steel in a hot filament chemical vapor deposition (CVD) reactor. The main drawbacks to overcome are the diamond film high residual stresses caused by the difference between the coefficient of thermal expansion (CTE) of steel (∼12 × 10−6 K−1) and diamond (0.8 × 10−6 K−1). Our group proposed a diffusion vanadium carbide (VC) interlayer as a potential solution to mitigate carbon dissolution in the substrate and graphite formation instead of diamond; however, the intermediate CTE of VC still provides high thermal stress and delamination of the film. A solution was proposed by performing the diamond CVD on the AISI O1 steel substrate above the steel austenitizing temperature, under the prospect that thermal stress will be minimized during cooling, since the return of steel from faced-centered cubic to body-centered cubic crystalline structures will cause substrate expansion. The lower residual stress was accomplished by the diamond growth temperature of 840 °C with all the steel substrate above the austenitizing critical temperature. The residual stress mitigation was 3.9 GPa, merging VC interlayer and high growth temperature, where numerical simulation exposed the same stress created by the growth temperature at 545 °C.

Effect of the Gaseous Atmosphere in GaAs Films Grown by Close-Spaced Vapor Transport Technique

The effect of the gaseous atmosphere in the growth of gallium arsenide (GaAs) films was studied. The films have been grown by close-spaced vapor transport (CSVT) technique in a home-made hot filament chemical vapor deposition (HFCVD) reactor using molecular hydrogen and molecular nitrogen as the transport agent. An important point about the gaseous atmosphere is the ease in creating volatile compounds when it makes contact with the GaAs source, this favors the transport of material in a CSVT system. Chemical reactions are proposed in order to understand the significant difference produced from the gaseous atmosphere. The films grown with hydrogen are (almost) continuous and have homogeneous layers with preferential orientation (111). The films grown with nitrogen are granular and rough layers with the coexistence of the orientations (111), (220) and (311) in the crystals. The incorporation of impurities in the films was corroborated by energy dispersive spectroscopy (EDS) showing traces of oxygen and nitrogen for the case of the samples obtained with nitrogen. Films grown in a hydrogen atmosphere show a higher band gap than those grown in a nitrogen atmosphere. With the results of XRD and micro-Raman we observe a displacement and broadening of the peaks, characteristic of a structural disorder. The calculations of the FWHM allow us to observe the crystallinity degree and determine an approximate crystallite size using the Scherrer’s equation.

Highly Visible Photoluminescence from Ta-Doped Structures of ZnO Films Grown by HFCVD

Tantalum-doped ZnO structures (ZnO:Ta) were synthesized, and some of their characteristics were studied. ZnO material was deposited on silicon substrates by using a hot filament chemical vapor deposition (HFCVD) reactor. The raw materials were a pellet made of a mixture of ZnO and Ta2O5 powders, and molecular hydrogen was used as a reactant gas. The percentage of tantalum varied from 0 to 500 mg by varying the percentages of tantalum oxide in the mixture of the pellet source, by holding a fixed amount of 500 mg of ZnO in all experiments. X-ray diffractograms confirmed the presence of zinc oxide in the wurtzite phase, and metallic zinc with a hexagonal structure, and no other phase was detected. Displacements to lower angles of reflection peaks, compared with those from samples without doping, were interpreted as the inclusion of the Ta atoms in the matrix of the ZnO. This fact was confirmed by energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD) measurements. From scanning electron microscopy (SEM) images from undoped samples, mostly micro-sized semi-spherical structures were seen, while doped samples displayed a trend to grow as nanocrystalline rods. The presence of tantalum during the synthesis affected the growth direction. Green photoluminescence was observed by the naked eye when Ta-doped samples were illuminated by ultraviolet radiation and confirmed by photoluminescence (PL) spectra. The PL intensity on the Ta-doped ZnO increased from those undoped samples up to eight times.

Adherent HFCVD diamond on steels substrates using vanadium carbide intermediate layer

Investigations on CVD diamond deposition on steels for high performance tools development persisted over years. Literature makes out the need for an intermediate layer to improve adhesion and film quality. This work studied Thermo Diffused Vanadium Carbide (TDVC) coating deposited on AISI O1 steel by thermo reactive diffusion (TRD). Thick TDVC layers formed by varying the thermo diffusion time from 1 h to 12 h. Hot Filament Chemical Vapor Deposition reactor (HFCVD) growth conditions variation made possible diverse diamond films growth, from ultrananocrystalline to microcrystalline. X-ray diffraction, scanning electron microscopy with a field emission gun (FEG-SEM) and Raman spectroscopy were the characterization techniques used. The TDVC coating showed up as an excellent diffusional barrier and, also, a compressive stress reliever. The thicker high quality and adherent HFCVD diamond film grown over the TDVC had a thickness of 3 μm. A TDVC cross-section of 35 μm thickness could effectively mitigate diamond residual thermal compressive stress state after cooling.

Effect of Argon Addition on Properties of the Boron-Doped Diamond Electrode

A boron-doped diamond(BDD) electrode is attractive for many electrochemical applications due to its distinctive properties: an extremely wide potential window in aqueous and non-aqueous electrolytes, a very low and stable background current and a high resistance to surface fouling. An Ar gas mixture of H2, CH4 and trimethylboron (TMB, 0.1% C3H9B in H2) is used in a hot filament chemical vapor deposition(HFCVD) reactor. The effect of argon addition on quality, structure and electrochemical property is investigated by scanning electron microscope(SEM), X-ray diffraction(XRD) and cyclic voltammetry(CV). In this study, BDD electrodes are manufactured using different Ar/CH4 ratios (Ar/CH4 = 0, 1, 2 and 4). The results of this study show that the diamond grain size decreases with increasing Ar/CH4 ratios. On the other hand, the samples with an Ar/CH4 ratio above 5 fail to produce a BDD electrode. In addition, the BDD electrodes manufactured by introducing different Ar/CH4 ratios result in the most inclined to (111) preferential growth when the Ar/CH4 ratio is 2. It is also noted that the electrochemical properties of the BDD electrode improve with the process of adding argon.

A Novel Approach to the Layer-Number-Controlled and Grain-Size-Controlled Growth of High Quality Graphene for Nanoelectronics

Thermal chemical vapor decomposition of methane on copper is the most widely employed technique for high quality and large area graphene growth. Graphene growth by this technique tends to be limited to a monolayer owing to the surface mediated self-limiting growth mechanism, and hence, it is difficult to obtain continuous bilayers and multilayers. We report the layer-controlled growth of high quality and large area polycrystalline graphene on copper foil in a hot filament chemical vapor deposition (HFCVD) reactor and demonstrate that graphene can be grown with a controlled grain size in the range of 5–16 μm. The field effect hole mobilities of the largest grain monolayer and bilayer graphene and the thickest few-layer graphene are 4310 ± 348, 2745 ± 276, and 2472 ± 185 cm2V–1s–1, respectively, which are comparable to that of high quality polycrystalline graphene and suitable for future nanoelectronics. The results of the systematic parametric study hereby presented indicate that graphene adlayers grow on ...

Thin-film nanocomposites of BDD/CNT deposited on carbon fiber

The nanocomposites of porous boron-doped diamond deposited on carbon nanotubes (BDD/CNTs) present great surface area and high capacitance, making them a material of considerable interest for application in electrochemistry. In this work, we present a new approach in which this nanocomposite is deposited on carbon fiber (CF) to increase the surface area and the capacitance comparing to the unsized CF electrode. We performed the dip-coating for catalyst deposition on CF surface. After, CNTs growth followed in a tubular reactor at 650°C for 20min, using camphor in a 200g/L hexane solution as the carbon source. Electrostatic Self Assembly (ESA) seeding of nanodiamond (ND) went on by grafting polar groups onto CNTs surface by oxygen plasma functionalization. The seeding process was made with 4nm diamond nanoparticles dispersed in KCl aqueous solution. The BDD films were deposited by Hot Filament Chemical Vapor Deposition (HFCVD) reactor. The authors studied the composites morphology, structure and electrochemical properties by Scanning Electron Microscopy with Field Emission Gun (FEG-SEM), Raman spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This new material presented larger surface area and higher capacitance compared to CF without treatment, as presented in electrochemical analysis results. The SEM micrographs showed absence of metallic particles on CNTs structure, what promoted a better quality diamond growth.

Boron doped micro/nanocrystalline diamond electrodes used on the electrochemical flow reactor to degrade brilliant green dye

ABSTRACTA systematic study was performed concerning the production, characterization, and application of BDD and BDND films grown on Ti substrate to degrade brilliant green dye using an electrochemical flow reactor. Films were grown in a hot filament chemical vapour deposition (HFCVD) reactor using H2/CH4 (BDD) and H2/CH4/Ar (BDND) gas mixtures. Boron doping was performed by dissolution of B2O3 in methanol in the appropriate B/C ratio to obtain good conductive electrodes. The electrolysis was carried out using BDD/Ti and BDND/Ti as anode material analyzing the influence of different current densities and flow rates. During the electrolysis, aliquots of the treated solution were analyzed by UV-Vis and Total Organic Carbon (TOC) measurements. The electrode efficiencies were compared considering the color removal as well as the TOC mineralization in the end of each electrolysis. The absorption bands intensity from UV/Vis spectra clearly decreased up to their completely vanishing at current density of 100 mA/cm2 for both electrodes. These results were corroborated by TOC measurements where 50% of the organic material was removed.

Interplay between adhesion and interfacial properties of diamond films deposited on WC-10%Co substrates using a CrN interlayer

In this study, the effect of deposition temperature on the adhesion of diamond films deposited on WC-10%Co substrates with a Cr-N interlayer is investigated. Diamond films were deposited at different temperatures (550, 650 and 750°C), using a hot filament chemical vapor deposition reactor. It was found that the optimal adhesion is obtained for the film deposited at 650°C. The interplay between carbon interfacial diffusion and the adhesion of diamond films deposited at different deposition temperatures were investigated. The combined use of different characterization techniques (Indentation tests, SIMS, XPS, XRD and SEM) shows that the adhesion strength depends on the thickness of Cr-C layer formed at the interface during diamond deposition, which is strongly influenced by the deposition temperature. It is suggested that at the optimum deposition temperature, thickness of the Cr-C layer is too low to introduce a large thermal stress at the interface and sufficiently thick enough to withstand the propagation of indentation induced cracks.

Mechanical Property and Characterization on Diamond Films Deposited on WC-Co Substrates

Cutting tools of WC-Co are widely used in cutting field. Nevertheless, its wear resistance and lifetime are not qualified for the high performance cutting. Therefore, diamond films are deposited on WC-Co substrates to overcome its disadvantages. In this paper we investigate the effects of the pretreatment on substrates and as-deposited WC-Co samples by using a hot filament chemical vapor deposition (HFCVD) reactor. Prior to deposition, the WC-Co substrates were submitted to surface roughening by Murakami reagent and to surface binder removal by Caro’ acid with varied durations. Surface roughness Ra determined by AFM varied from 110 to 279 nm. The diamond films are characterized by scanning electron microscopy (SEM) and Raman spectroscopy, whose results present a sharp peak at 1336 cm-1 indicating sp3 diamond. The adhesion between the diamond films and substrates was evaluated by pull-off tests with the highest adhesion strength is 26.92 MPa. Cracked interface is characterized between diamond films and substrates, using SEM and energy dispersive spectroscopy (EDS) to analyze the adhesion performance.

Effect of Argon during Diamond Deposition by Hot Filament Chemical Vapor Deposition

The effect of argon content upon the growth rate and the properties of diamond thin films grown with different grains sizes are explored. An argon-free and argon-rich gas mixture of methane and hydrogen is used in a hot filament chemical vapor deposition reactor. Characterization of the films is accomplished by scanning electron microscopy, Raman spectroscopy and high-resolution x-ray diffraction. An extensive comparison of the growth rate values and films morphologies obtained in this study with those found in the literature suggests that there are distinct common trends for microcrystalline and nanocrystalline diamond growth, despite a large variation in the gas mixture composition. Included is a discussion of the possible reasons for these observations.

Gas phase generation of diamond nanoparticles in the hot filament chemical vapor deposition reactor

A possibility for the new synthesis method of diamond nanoparticles is studied using a hot filament chemical vapor deposition (HFCVD) reactor. Considering the growth mechanism of diamonds at low pressure from the well-known observation of simultaneous diamond deposition and graphite etching without violating the second law of thermodynamics, diamond nanoparticles should be generated in the gas phase. To confirm the generation of diamond nanoparticles in the gas phase under the synthesis condition of diamond films by HFCVD, the transmission electron microscope (TEM) grid membrane was exposed for 3–15 s using a capturing apparatus and the grid membrane was observed by TEM. The number density of captured nanoparticles increased with increasing capture time whereas the size of them was changed only slightly. In addition, to confirm whether the nanoparticles are electrically charged or not, the electric bias was applied to the stainless steel plate placed below the holder of the TEM grid. The positive bias increased the number density of nanoparticles whereas the negative bias decreased it, indicating that nanoparticles are negatively charged. The TEM images showed that the captured nanoparticles had a diameter of 4–6 nm and 0.206 nm of crystalline lattice spacing, which indicates the {111} plane of diamond.

Boron-doped diamond electrodes for carbofuran electrochemical degradation

Boron-doped diamond electrodes were produced on titanium substrate by Hot Filament Chemical Vapor Deposition reactor for electrochemical degradation of carbofuran pesticide. The morphological and structural characterizations of the electrodes were evaluated by Scanning Electron Microscopy and by Raman scattering Spectroscopy techniques. The apparent space charge density (NA) value was determined by Mott-Schottky Plot, which is approximately 1019 cm-3. The electrochemical characterization of electrodes was performed by Cyclic Voltammetry, and it was observed large potential windows. The electrochemical oxidation of the carbofuran were performed at different current densities, flow rates of 50 and 300 Lh-1 for a total of 2 hours with an electrolyte aqueous solutions K2SO4 0.1M and carbofuran concentration of 1,8 x 10-3 M in a flow reactor with recirculation. The efficiency of the pesticide degradation process was monitored by UV–Vis Spectrophotometry, Total Organic Carbon (TOC) and High Performance Liquid Chromatography (HPLC) techniques. The obtained results show that Ti/BDD anodes are promising for electrochemical treatment in the wastewater. The reducing the TOC concentration promoted a breakdown of the carbofuran molecule rather than the mineralization of organic matter. This fact may have contributed to the formation of carbofuran intermediates resulting from the reaction of degradation of the pesticide.

Boron-Doped Nanocrystalline Diamond Grown on Reticulated Vitreous Carbon: Morphological, Structural, and Electrochemical Characterizations

Composites formed from diamond grown on carbonaceous materials have been showed special attention due to their remarkable properties for electrochemical applications. In this sense, boron-doped nanocrystalline diamond (BDND) films were grown on reticulated vitreous carbon (RVC) substrates produced from poly(furfuryl alcohol) at two heat treatment temperatures (HTT) of 1000 °C and 1700 °C. The films were produced from hot filament chemical vapor deposition reactor with an in-situ doping process in the gas phase. Scanning electron microscopy and Raman spectroscopy analyses confirmed that both RVC electrodes were totally covered by good quality nanodiamond coatings with acceptor concentrations at around 1020 B.cm-3, evaluated by Mott-Shottky measurements. Both RVC/BDND composites presented good electrochemical response in redox couple. Nonetheless, RVC/BDND1700 showed the best conductivity due to its lowest variation of ΔEp value as well as its highest electrochemical area. These results demonstrate that RVC/BDND1700 is a very promising electrode material.

Micro, Nano and Ultranano-Crystalline Diamond Deposition

This is a comparative experimental study of the micro, nanoand ultranano-crystalline diamond deposition. The Hot Filament Chemical Vapor Deposition (HFCVD) reactor deposits the films using different deposition parameters. Scanning Electron Microscopy and Field Emission Scanning Electron Microscopy let morphology inspection. Visible-Raman scattering loaded to estimating relative induced stress, by the graphite peak shift and associated with the defect incorporation and sp2 bond enhancement. The x-ray diffraction confirmed the diamond crystallinity, where Scherrer ́s equations estimate crystallite size and diamond renucleation rates. In this work we propose a defect increasing relative graphite incorporation with the transition of micro, nanoto ultranano-crystalline diamond deposition. Besides this, we propose that this increase defects follows the increase diamond renucleation rates and decreases in the induced stress films. Included is a discussion of the possible reasons for these observations.

Large-area bilayer graphene synthesis in the hot filament chemical vapor deposition reactor

We fabricated large area bilayer graphene by hot filament chemical vapor deposition (HFCVD) on Cu foil. The HFCVD technique can represent a significant advantage over other techniques for industrial scaling at low cost. We performed systematic experiments to determine the best parameters to obtain uniform graphene coverage over an area of ~16cm2. The experimental growth parameters are grouped into two distinct regions according to the products obtained: (A) continuous bilayer graphene with low defect density and (B) continuous bilayer graphene with high defect density. The optimum graphene films obtained are uniform bilayer with low defect density, greater than 90% transmittance in the visible region, and no gaps. The high quality of the bilayer graphene was confirmed by Raman spectroscopy mapping. The results show that the ratio of 2D to G peak intensities (I2D/IG) is in the 0.9–1.6 range over 90% of the area. Moreover, we employed the static cling property of polyethylene terephthalate (PET) to preserve the integrity of the as-grown graphene films in the transfer process, showing that the graphene films become well attached to the SiO2/Si substrates while the PET films were completely peeled off.

Activation energies for the growth of diamond films and the renucleation of diamond grains during film growth

The effect of substrate temperature upon the growth rate and the properties of diamond thin films grown with different grains sizes is explored. An argon-free and argon-rich gas mixture of methane and hydrogen is used in a hot filament chemical vapor deposition reactor. Characterization of the films is accomplished by scanning electron microscopy, Raman spectroscopy and high-resolution x-ray diffraction. Arrhenius plots of the mass gain, thickness growth, and renucleation rate as a function of the substrate temperature are used to obtain the values of the activation energies. An extensive comparison of the activation energy values obtained in this study with those found in the literature suggests that there are distinct common trends for microcrystalline and ballaslike diamond growth. Besides the activation energy values, the morphology, crystallite size, sp2 quantification, mass gain, thickness growth, and renucleation rate present similar tendencies with the substrate temperature, despite a large variation in the gas mixture composition. Included is a discussion of the possible reasons for these observations.

Low Resistance Polycrystalline Diamond Thin Films Deposited by Hot Filament Chemical Vapour Deposition

Polycrystalline diamond thin films with outgrowing diamond (OGD) grains were deposited onto silicon wafers using a hydrocarbon gas (CH4) highly diluted with H2 at low pressure in a hot filament chemical vapour deposition (HFCVD) reactor with a range of gas flow rates. X-ray diffraction (XRD) and SEM showed polycrystalline diamond structure with a random orientation. Polycrystalline diamond films with various textures were grown and (111) facets were dominant with sharp grain boundaries. Outgrowth was observed in flowerish character at high gas flow rates. Isolated single crystals with little openings appeared at various stages at low gas flow rates. Thus, changing gas flow rates had a beneficial influence on the grain size, growth rate and electrical resistivity. CVD diamond films gave an excellent performance for medium film thickness with relatively low electrical resistivity and making them potentially useful in many industrial applications.