Hot-filament Chemical Vapor Deposition Reactor Research Articles

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

AbstractLarge area single and bilayer graphene are grown on Pt/Ti/SiO2 substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO2 substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO2 substrate at a low filament temperature. The approach paves a novel pathway towards the layer‐controlled growth of graphene on Pt/Ti/SiO2 substrates by HFCVD for frontier applications.

Numerical calculation of temperature, velocity, and species concentration distributions in a hot filament chemical vapor deposition in a reactor using a CH4/H2 mixture

This study is a numerical modeling of transport phenomena occurring in the reaction chamber during diamond or amorphous hydrogenated carbon films growth by a hot filament chemical vapor deposition (HFCVD) technique. A two-dimensional model was adopted to study the HFCVD reactor. The equations of heat, momentum, and mass transfer were solved numerically; the simulation was performed using a program in FORTRAN language. All temperature, velocity, and species concentration distributions were similar at the filaments and they were also similar between the filaments. The results show that the gas temperature increases when the number of filaments increases from three to four filaments. We also noted an increase in the production of CH3 and C2H5 radicals near the surface; there was also an increase in the growth rate of the thin film. The concentrations of C2H6, C2H4, and C2H5 were very high. Temperature and concentrations were affected by the distance between filaments and the distance filaments-substrates.

Comparison of diamond nanoparticles captured on the floating and grounded membranes in the hot filament chemical vapor deposition process.

Negatively charged diamond nanoparticles are known to be generated in the gas phase of the hot filament chemical vapor deposition (HFCVD) process. However, the structures of these nanoparticles remain unknown. Also, the effect of charging on the stability of nanodiamond structures has not been studied experimentally. Here, by installing a capturing apparatus in an HFCVD reactor, we succeeded in capturing nanoparticles on the floating and grounded SiO, carbon, and graphene membranes of a copper transmission electron microscope grid during HFCVD. We examined the effect of charge on the crystal structure of nanodiamonds captured for 10 s under various conditions and identified four carbon allotropes, which are i-carbon, hexagonal diamond, n-diamond, and cubic diamond, by analyzing 150 d-spacings of ∼100 nanoparticles for each membrane. Nanoparticles captured on the floating membrane consisted mainly of cubic diamond and n-diamond, whereas those captured on the grounded membrane consisted mainly of i-carbon. Diamond particles deposited for 8 h on the floating silicon (Si) substrate exhibited an octahedron shape with well-developed facets, and a high-intensity 1332 cm−1 Raman peak, whereas diamond particles deposited on the grounded Si substrate showed a spherical shape partially covered with crystalline facets with a broad G-band Raman peak. These results indicate that charging stabilizes the diamond structure.

A simple procedure to obtain nanodiamonds from leftover of HFCVD system for biological application

Nanodiamonds (NDs) are amongst the most investigated carbon-based nanostructures due to their chemical stability and favorable mechanical properties. Despite the number of works on methods for NDs production, one of the main challenges is to achieve their colloidal stability in aqueous suspension. Additionally, NDs are normally obtained by expensive, complex and time-consuming process. Herein, it was presented a facile method to obtain NDs in aqueous suspension by using columnar structure diamond from Hot-Filament Chemical Vapour Deposition reactor (HFCVD). CVD diamond leftover thick film from CVDVale Company was used. Therefore, this method has the advantage of being not only practical but also cost-effective since it brings a profitable use of CVD diamond leftover. The Diamond thick film was submitted to ultrasonic cavitation in the presence and absence of ZrO2 microbeads in aqueous medium. The NDs hydrodynamic diameter and the stability in aqueous suspension were monitored by light scattering, size and morphology were analyzed by transmission electronic microscopy. Considering the wide application of NDs in biomedical devices, cytotoxicity of aqueous suspensions of NDs was evaluated against murine embryonic fibroblast cells. Furthermore, NDs were functionalized with hydrogen and carboxyl groups. NDs aqueous suspension of straight size distribution was obtained even in the absence of ZrO2 beads, indicating that they may be dispensable in order to decrease NDs size. NDs of average hydrodynamic diameter of 22 nm and − 35 mV of Zeta-potential were obtained after ultrasonic cavitation followed by 2 h of centrifugation, not demonstrating cytotoxicity to cells at very low (0.05–0.5 μg/mL) nor at higher concentrations (116 μg/mL). Nevertheless, NDs showed a moderate cytotoxicity at intermediary concentration range (0.5–2.2 μg/mL). From our knowledge, this is the first work that reports on a facile method for providing NDs aqueous suspension with high colloidal stability from HFCVD diamond leftover.

Computer Simulation of Temperature Parameter for Diamond Formation by Using Hot-Filament Chemical Vapor Deposition

To optimize the deposition parameters of diamond films, the temperature, pressure, and distance between the filament and the susceptor need to be considered. However, it is difficult to precisely measure and predict the filament and susceptor temperature in relation to the applied power in a hot filament chemical vapor deposition (HF-CVD) system. In this study, the temperature distribution inside the system was numerically calculated for the applied powers of 12, 14, 16, and 18 kW. The applied power needed to achieve the appropriate temperature at a constant pressure and other conditions was deduced, and applied to actual experimental depositions. The numerical simulation was conducted using the commercial computational fluent dynamics software ANSYS-FLUENT. To account for radiative heat-transfer in the HF-CVD reactor, the discrete ordinate (DO) model was used. The temperatures of the filament surface and the susceptor at different power levels were predicted to be 2512–2802 K and 1076–1198 K, respectively. Based on the numerical calculations, experiments were performed. The simulated temperatures for the filament surface were in good agreement with the experimental temperatures measured using a two-color pyrometer. The results showed that the highest deposition rate and the lowest deposition of non-diamond was obtained at a power of 16 kW.

New method for the growth of single-walled carbon nanotubes from bimetallic nanoalloy catalysts based on Prussian blue analog precursors

Catalyst engineering is a key point for selective growth of single-walled carbon nanotubes (SWCNT) with chemical vapor deposition (CVD). Here, we develop a new general synthesis method able to produce a wide range of homogenous bimetallic catalyst nanoparticles with controlled stoichiometry and sizes. The basics of this catalyst synthesis is to use preformed stoichiometric bimetallic Prussian blue analog (PBA) nanoparticles. Catalyst nanoparticles are then prepared in-situ in a hot filament CVD reactor with subsequent high temperature treatment in reducing atmosphere prior to SWCNT growth. The capabilities of the synthesis route are demonstrated by testing five PBA systems involving various transition metals. Transmission electron microscopy (TEM), scanning TEM and energy dispersive X-ray spectroscopy (STEM-EDX), and in-situ X-ray photoelectron spectroscopy (XPS) measurements are used to finely follow the size and composition of the catalyst at each step of the process. Each system yields small size catalysts with a narrow distribution, which act as efficient catalysts for SWCNT growth with a good yield and small diameter distribution. The versatility of the PBA family paves a new way for a fine tuning of the catalyst properties monitored by the metal involved in the PBA, and for opening routes to more selective SWCNT synthesis.

Synthesis and Characterization of Carbon Fiber Based Porous CNTs-RGO/BDD for Application as Microelectrodes

ABSTRACTMicroelectrodes have attracted great interest for electroanalysis because of their unique properties, such as nonlinear diffusion, increased rate of mass transport and reduced capacitance, which allows a fast response. In this work, we created a porous nanocomposite of boron doped diamond (BDD) deposited on carbon nanotubes – reduced graphene oxide (CNTs – RGO) by Hot Filament Chemical Vapor Deposition (HFCVD) technique. The resulting material yielded porous BDD microelectrodes. On the first step, we have grown the CNTs on carbon fiber (CF) surface by Thermal CVD in a tubular reactor. Camphor solution and Fe-Co were carbon and catalyst source, respectively. For exfoliation, CNTs were treated by hydrogen plasma and oxygen plasma. We applied a seeding solution containing nanodiamond dispersed in KCl aqueous solution. Diamond nanoparticles interact with oxygen-containing groups on CNTs, promoting an efficient seeding. We deposited BDD films in an HFCVD reactor using methane/hydrogen gas mixtures. For doping, a partial hydrogen flow bubbled in a closed vessel containing a solution of boron oxide dissolved in methanol. The microelectrodes were characterized by Raman Scattering Spectroscopy, Scanning Electron Microscopy with Field Emission Gun and Cyclic Voltammetry. The crystalline quality of CNTs and BDD doping level were studied by Raman analysis. SEM micrographs showed that nanocomposite presented high porosity. Electrochemical analysis showed that the deposition of BDD on CNTs-RGO increased the electrochemical response of the microelectrode. Besides, this electrode presented a low capacitive current in comparison with BDD grown on flat substrates. Further, the porous BDD nanocomposite showed itself to be promising in electroanalysis.

Chemical Vapor Deposited Few-Layer Graphene as an Electron Field Emitter.

Chemical vapor deposition (CVD) growth of graphene on polycrystalline copper (Cu) foil in a low pressure conditions has been presented, aiming to achieve the highest quality with large-scale fabrications, which requires comprehensive understanding and effective controlling of the growth process. Herein, few-layer graphene (FLG) films with large-domain sizes were grown on Cu metal catalyst substrates using a vertical mass-flow hot-filament CVD reactor, with the intention of large scale production, by optimizing the CVD system and three of the process parameters: (i) gas flow compositions, (ii) substrate annealing time and (iii) graphene deposition time. The detailed scanning electron microscope and Raman spectroscopy analysis indicate that all the above mentioned process parameters affect growth of FLG film on Cu substrate. The presence of two intense peaks, G and 2D-band at 1583.6 and 2702.6 cm⁻¹ for synthesized sample at optimized conditions (H₂/CH₄ ratio of 50:1 at graphene deposition time of 10 minutes and substrate annealed time for 20 minutes) revealed the formation of FLG films with large domain size. These graphene films on Cu have shown the room temperature field electron emission characteristics, hence appears to be prospective candidate for vacuum nanoelectronics.

SIMULATION OPTIMIZATION OF THE HEAT TRANSFER CONDITIONS IN HFCVD DIAMOND FILM GROWTH INSIDE HOLES

Finite volume method (FVM) is adopted in the present investigation to simulate the temperature and reactant gas velocity distributions in hot filament chemical vapor deposition (HFCVD) diamond film growth inside holes, using a detailed 3D computational model well in accordance with the actual reactor. The influences of the heat transfer characteristic of the substrate and the auxiliary heat transfer conditions are firstly studied by control variable method (CVM), including the thermal conductivity of the substrate k, the size of the red bronze support block V(x × y × z), the cooling water flux Qw, the reactant gas flux Qg, the arrangement of the gas outlets A out and the emissivities of the different solid surfaces ϵ. Thereafter, the substrate temperature data measured in the actual HFCVD reactor with three chosen groups of parameters are compared with those obtained from the simulations, presenting similar trends and small deviations less than 5%. Moreover, the auxiliary heat transfer conditions are optimized for both the WC- Co and SiC substrates based on the simulation and measurement results, and corresponding deposition parameters are also determined. Furthermore, HFCVD diamond films are deposited on the inner surfaces of both the substrates under the optimized conditions. The characterization results show that high-quality diamond films with uniform thickness and fine-faceted crystals are obtained, indicating that this optimization method focusing on the heat transfer conditions is feasible and correct.

Study of diamond nucleation and growth on Ti6Al4V with tungsten interlayer

Diamond nucleation and growth on Ti6Al4V substrates with tungsten (W) interlayers were investigated using hot filament chemical vapor deposition (HFCVD). W interlayers were firstly deposited on Ti6Al4V substrates under different conditions by sputtering and diamond was then deposited on W-coated Ti6Al4V using the same HFCVD reactor. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy, Raman spectroscopy, synchrotron near-edge X-ray absorption fine structure spectroscopy and Rockwell C indentation tests were used for characterization. The effect of thickness and surface morphology of W interlayer on the nucleation, growth, and adhesion of diamond on the Ti alloy was investigated. The results show that the pre-deposited W interlayers act as a diffusion barrier for carbon, and thus significantly enhancing the nucleation of diamond. In addition, the W interlayer reacts with carbon to form WC and W2C during the diamond deposition, thus enhancing the adhesion of diamond on Ti6Al4V.

Study of CrNx and NbC interlayers for HFCVD diamond deposition onto WC–Co substrates

Chromium nitride (CrNx) and niobium carbide (NbC) films were deposited by magnetron sputtering on Co-cemented tungsten carbide (WC–Co) substrates and diamond deposition was performed by using hot-filament chemical vapor deposition (HFCVD) technique. The CrNx and NbC interlayers have been deposited at different substrate temperatures (TS=400, 550 and 700°C). The stability of these interlayers for diamond deposition has been studied by a heat treatment in H2 atmosphere for 60h at a temperature of 765°C in the HFCVD reactor. X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES) confirmed that due to this heat treatment the CrNx films transformed into porous films composed of CrNx, Cr3C2, Cr7C3 and Co phases, accompanied by a dramatic loss of nitrogen which is replaced by carbon. It was observed that higher nitrogen contents in the CrNx films reduce the Co diffusion through the CrNx layer. For NbC films, deposited by non-reactive magnetron sputtering from an NbC compound target, the heat treatment in the HFCVD reactor revealed that the films are absolutely stable during the heat treatment with some relaxation of residual stresses up to a factor of about 3. Furthermore it was found that Co diffuses through the NbC films with a TS-dependant accumulation on the NbC film surface. By HFCVD it was possible to deposit adherent diamond coatings on the CrNx and NbC interlayers. However, a reasonable adhesion of diamond on NbC was only obtained after different pre-treatments of the WC–Co substrates. The adhesion seems to be mainly governed by the topography of the WC–Co substrates.

Structural Properties of Zn‐ZnO Core‐Shell Microspheres Grown by Hot‐Filament CVD Technique

We report the hot‐filament chemical vapor deposition (HFCVD) growth of Zn‐ZnO core‐shell microspheres in the temperature range of 350–650°C only using ZnO pellets as raw material. The samples were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X‐ray diffraction (XRD) techniques. SEM micrographs showed the presence of solid microspheres and a Zn‐ZnO layer in all samples. The observed heterogeneous morphology on each sample suggested two different growth mechanisms. On the one hand, solid microspheres were formed by means of gas phase nucleation of Zn atoms. The Zn‐ZnO layer was formed on the substrate as result of surface reactions. It is possible that Zn microspheres condensed during the natural cooling of the HFCVD reactor as they were observed on the Zn‐ZnO layer.

Simultaneous growth of diamond and nanostructured graphite thin films by hot-filament chemical vapor deposition

Diamond and graphite films on silicon wafer were simultaneously synthesized at 850 °C without any additional catalyst. The synthesis was achieved in hot-filament chemical vapor deposition reactor by changing distance among filaments in traditional gas mixture. The inter-wire distance for diamond and graphite deposition was kept 5 and 15 mm, whereas kept constant from the substrate. The Raman spectroscopic analyses show that film deposited at 5 mm is good quality diamond and at 15 mm is nanostructured graphite and respective growths confirm by scanning auger electron microscopy. The scanning electron microscope results exhibit that black soot graphite is composed of needle-like nanostructures, whereas diamond with pyramidal featured structure. Transformation of diamond into graphite mainly attributes lacking in atomic hydrogen. The present study develops new trend in the field of carbon based coatings, where single substrate incorporate dual application can be utilized.

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.

Formation mechanism of diamond nanotips by plasma enhanced vapour processes

Synthesis of diamond nanotip arrays was investigated using plasma enhanced hot filament chemical vapour deposition (HFCVD) and microwave plasma enhanced chemical vapour deposition (MPCVD) under different conditions. Well-aligned diamond nanotip arrays were synthesized on silicon wafers precoated with diamond thin films with substrates negatively biased in a plasma in the HFCVD reactor with a negative bias voltage above 300 V and the operation pressure below 2 kPa. The alignment orientation of the nanotips is parallel to the electric field lines on the sample surface. All the nanotips synthesized have nanometre-size tips and micrometre-size roots. The apex angle of the nanotips is similar under the same conditions regardless of the size of the nanotips. However, only flat diamond thin films were obtained when MPCVD was used regardless of the processing conditions. The experimental results indicate that the formation of nanotips strongly depends on ion bombardment and the nanotip apex angle is determined mainly by ion bombardment conditions regardless of the size of the nanotips. An angle dependent ion sputtering mechanism was proposed to explain the formation of nanotips. Furthermore, controlled ion beam sputtering of precoated diamond thin films was conducted in an ion beam deposition system to verify the formation mechanism.

Role of Duty Ratio in Diamond Growth by Pulsed DC-Bias Enhanced Hot Filament Chemical Vapour Deposition

In this study, the role of the pulse duty ratio was investigatedduring the deposition of diamond films in a hot filament chemicalvapour deposition reactor with a pulsed-dc biased substratepositively relative to the hot filaments. The voltage-currentcharacteristics showed that the discharge current rose with theincrease of biasing voltage, which was modified by the duty ratio.Before deposition, two approaches were adopted for the pre-treatmentof the silicon substrates, respectively, and the substrates werescratched by diamond paste or seeded by diamond powders using theso-called `soft dry polished' technique. Diamond films weredeposited under a fixed discharge power by changing the duty ratios.In the first group with scratched substrates, it was found thatunder a high duty ratio the diamond grew slowly with quite poornucleation, while in the second case a high duty ratio induced ahigh deposition rate and good diamond quality. Reactive hydrocarbonspecies with high energy are essential for the initial nucleationprocess, which is more effectively achieved at a high biasingvoltage in the condition of a low duty ratio. In the film growthprocess, the large discharge current at a high duty ratio representsan increased concentration of electrons and reactive species aswell, promoting the growth of diamond films.

Bias enhanced diamond nucleation on Mo and CrN coated stainless steel substrates in a HFCVD reactor

Bias enhanced nucleation was explored in order to obtain a high diamond nucleation density on Mo and CrN coated stainless steel substrates in a hot-filament chemical vapor deposition (HFCVD) reactor. Several bias geometries were tested on their nucleation enhancement for diamond on molybdenum. It was found that the nucleation properties observed for Mo were not much different for CrN coated stainless steel. The application of a bias between the filament and a cathode above the substrate at floating potential resulted in locally high diamond nucleation densities of up to 3∙10 9 cm − 2 .

A computational model for the hot-filament chemical vapour deposition process to produce diamond films

A two-dimensional computational model for the hot-filament chemical vapour deposition (HFCVD) process to produce diamond films is presented. The model solves the overall continuity, momentum, energy and species continuity equations inside the reaction chamber of a HFCVD reactor. The gas-phase homogeneous reactions are represented by a simplified reaction mechanism. The model incorporates the catalytic production of H radical at the filament surface. Expressions representing the recombination of the H radical at surfaces and the growth rate of diamond film on the substrate were coupled to the gas-phase transport equations. The computational model was solved numerically by means of a commercial software. The model predictions showed good agreement with the experimental data reported in the literature in terms of both gas temperature and CH3 concentration profiles along the filament-to-substrate centre distance and with experimental data of the growth rate of diamond films obtained in a laboratory HFCVD reactor. Numerical simulations considering one, three and five filaments were conducted. The results showed that as the number of filaments increases, the concentration of CH3 in the reaction chamber increases as well as the rate of growth of the diamond film being produced. The shape and dimensions of the reaction chamber, filaments and substrate were found to significantly affect the model predictions. Therefore, the use of computational fluid dynamics techniques in the analysis of HFCVD reactors must be exercised with caution.

Low-Temperature Formation of Well-Aligned Nanocrystalline Si/SiOx Composite Nanowires

Well-aligned nanocrystalline (nc)-Si/SiOx composite nanowires have been deposited on various substrates at 120 °C using SiCl4/H2 in a hot-filament chemical vapor deposition reactor. Structural and compositional analyses reveal that silicon nanocrystals are embedded in the amorphous SiOx nanowires. The nc-Si/SiOx composite nanowires are transparent in the range 500–900 nm. Photoluminescence spectra of the nc-Si/SiOx composite nanowires have a broad emission band, ranging from 420 to 525 nm. Water vapor from the chamber wall plays a crucial role in the formation of the well-aligned nanowires. A possible mechanism for the formation of the composite nanowires is suggested.

Effects of CCl 4 concentration on nanocrystalline diamond film deposition in a hot-filament chemical vapor deposition reactor

The effect of CCl 4 concentration on the nanocrystalline diamond (NCD) films deposition has been investigated in a hot-filament chemical vapor deposition (HFCVD) reactor. NCD films with a thickness of few-hundred nanometers have been synthesized on Si substrates from 2.0% and 2.5% CCl 4/H 2 at a substrate temperature of 610 °C. Polycrystalline diamond films and nanowall-like films with higher formation rates than those of the NCD films were deposited from lower and higher CCl 4 concentrations, respectively. The grain sizes of the diamond film grown using 2.0% CCl 4 increased with film thickness while a diamond film with uniform nanocrystalline structure all over a thickness of 1 μm can be deposited in the case of 2.5% CCl 4. We suggest that both the primary nucleation and the secondary nucleation processes are crucial for the growth of the NCD films on Si substrates.