Hot Filament Assisted Chemical Vapor Deposition Research Articles

W Clusters In Situ Assisted Synthesis of Layered Carbon Nanotube Arrays on Graphene Achieving High-Rate Performance.

W atoms/clusters are employed to in situ assist the development of layered vertically aligned carbon nanotube arrays (VACNTs) through hot-filament-assisted chemical vapor deposition (HFCVD) with liquid binary Fe3O4/AlOx catalysts. The hot W filament was utilized to in situ evaporate atomic W and form W clusters on Fe catalysts, which have a strong impact on the growth of layered VACNT arrays. The migration and Ostwald ripening of Fe catalysts are found to be suppressed immediately with more W clusters deposition during CNT growth. Through controlling the deposition of W clusters, the electrochemical energy storage performance of as-prepared layered VACNT arrays is also tunable as electrodes of ion-based supercapacitors. The layered VACNT arrays can achieve a high capacity of 83.1 mF cm-2 and possess desirable rate performance due to the suitable hot filament condition (55 W for 90 s). This work provides a new perspective to in-depth understand the behavior of W filament during HFCVD and the significant role of the in situ generated W clusters on the growth of CNTs by maintaining the catalytic activity and structure of catalysts.

Diamond film growth by HFCVD on Q-carbon seeded substrate

While hot-filament assisted chemical vapor deposition (HFCVD) is a well-established technique to synthesize diamond thin films using microdiamond seeds, the quality of grown diamond thin films is often compromised due to the presence of contaminants, i.e. graphitic entities and the eroded tungsten filament remnants, at the film-substrate interface. Here, we present a novel approach to form high-quality, contamination-free diamond thin films with HFCVD using Q-carbon precursor. The Q-carbon is a metastable phase which is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the superundercooled state and consists of ∼75% sp3 and rest sp2 hybridized carbon. Using Q-carbon seeds in HFCVD, we demonstrate the growth of polycrystalline diamond film with a clean interface without any tungsten filament impurities. With large-area vibrational Raman mode analysis, we also observe a significant reduction in the presence of overall graphitic entities in the diamond film. With the realization of such a high-quality interface, we present a pathway to fabricate significantly improved diamond coatings and solid-state devices.

A new design of composites for thermal management: Aluminium reinforced with continuous CVD diamond coated W spiral wires

A novel design of Al matrix composite reinforced with diamond coated spiral tungsten wire is proposed for thermal management. Fabrication techniques of the diamond film reinforced Al matrix composites consist of hot filament assisted chemical vapour deposition (HFCVD) for diamond film, low-cost cold pressing and vacuum sintering of Al matrix composites. The microstructure characteristics and thermal properties of the composites have been studied. Results show that the diamond film retains its high quality and integrity after the vacuum sintering process. Even such a low content of diamond films in the filler- at most 6.5vol.% - provides a thermal conductivity of 294W/mK, about 69% higher than that of sintered Al and 79% higher than that of 6.5vol.% diamond particles reinforced Al matrix composite fabricated by the same powder metallurgy process. Finite element analysis of heat transfer within such a structure is conducted, revealing that the continuous and thick diamond framework provides continuous channels and effective thermal conductive pathways for heat transfer. This work displays a great potential of CVD diamond films reinforced metal matrix composites for thermal conduction applications.

Deposition of Boron Nitride Films by Filament-Assisted CVD Using Tris(Bimethylamino)Borane Precursor

Boron nitride films were deposited on silicon substrate by a hot filament assisted chemical vapor deposition (HFCVD) system. The tris (dimethylamino) borane (B[N(CH3)2]3) was used as the single source precursor which has both the boron and nitrogen source, ammonia gas was used as the assisted gas to increase the nitrogen concentration in the films. The films deposited by different ratios of precursor to ammonia gas flow rate and filament temperatures were investigated. The boron-carbon-nitrogen (BCN) compound films were deposited under lower filament temperature. With increasing the ammonia gas flow rate, the carbon concentration in the films decreased. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) image reveal that hexagonal boron nitride (hBN) films were deposited at the higher filament temperature of 2000°C. Moreover, the crystallization degree of the films became better with the filament temperature increased.

Characterization of Nitrogen Doped Diamond Electrodes Produced by Hot Filament Chemical Vapor Deposition

The purpose of this work is to study the structural and morphological modification of the surface of the n-type diamond electrodes as a function of nitrogen doping. The characterizations of these electrodes were made using Raman Spectroscopy, Contact Angle, X-ray diffraction and Scanning Electron Microscopy (SEM). The nitrogen-doped diamond (NDD) electrodes were produced using Hot Filament-assisted Chemical Vapor Deposition method (HFCVD) from methane, hydrogen and nitrogen in the gas mixture. The results from Raman spectroscopy show that the diamond films obtained with nitrogen addition presented one large band at 1100-1700 cm-1. The SEM images showed that the variation in the nitrogen doping influenced the growth rate of films by promoting changes in the sizes of grains from microcrystalline to nanocrystalline texture. This behavior supported the results obtained from X-ray diffraction analyses. It was possible to verify a decrease in the crystallite size as a function of the nitrogen increase.

Copper Electroless Process Optimization to Modify Boron Doped Diamond at Different Boron Levels

Composite of Cu/BDD (boron doped diamond) have the potential to use as solid electrode for application in environmental approaches. Among many Cu coating processes, the electroless plating has emerged in recent years due to its low cost, fast deposition rate, and good filling capability. In addition, its major advantage is its simplicity, where the processes can take place at room temperatures and pressures [1]. In the Cu electroless process, a hard pre-treatment is needed for cleaning the surface and for creating functional groups that can act as anchor points on the BDD samples. The pre-treatments can be obtained using different oxidation techniques. In this study the anodic electrochemical pre-treatment was carried out using 0.5 mol L-1 H2SO4 and a fixed potential of 3 V for 30 min. The present study was undertaken in order to investigate the influence of the BDD doping level in the electroless synthesis as well as the effect of some deposition parameters such as the solution pH and the deposition time, to obtain Cu/BDD composites. This material is very attractive for nitrate electroreduction related to environmental interest. BDD films were grown by hot filament-assisted chemical vapor deposition technique on the titanium substrate, activated by methane and hydrogen gas mixture with a pressure of 40 Torr, at 650ºC, for 24 h. Boron source was obtained by an additional hydrogen line passing through a bubbler containing B2O3 dissolved in methanol with a controlled B/C ratio that led to films with different doping level (5000 and 15000 ppm). Prior to the Cu electroless deposition, the sensitization on the BDD was achieved using a solution of 40 mL L-1 HCl containing 0.04 mol L-1 SnCl2 for 5 min and the activation was made using a solution containing 7x10-4 mol L-1 PdCl2 with 2.5 mL L-1 HCl for 5 min. Ultrasonic vibration was used for both steps. The electroless Cu deposition was carried out for different times (30, 60, 180 and 2400 s) at room temperature. The bath composition was 0.1 mol L-1 CuSO4 + 0.2 mol L-1 KNaC4H4O6 + 17.5 mL L-1 HCHO. The pH level was adjusted to 8, 10 and 12 by the addition of NaOH. The Raman scattering spectra showed the peak close to 1332 cm-1 corresponds to the vibration of a diamond first-order phonon, confirmed the quality of these BDD films. This peak decreased in intensity due to the boron incorporation in diamond films. The effect of boron doping is reflected in the spectral features. There is the appearance of the two bands located at 500 cm-1 and 1220 cm-1 attributed to B-B vibrations and B-C vibrations, respectively. According to Scanning Electron Microscopy images the Cu deposits showed an uniform particle distribution on the BDD surface for solution of pH 12. On the other hand, no Cu deposit was verified at pH 8 and at pH 10 in the range of time deposition from 30 to 180 s. However, for deposition time of 2400 s, the deposit presented low particle density. Similar experimental conditions for electroless Cu deposition on lightly doped diamond showed the same behavior as a function of pH. The Cu deposit rate increased with increasing the deposition time, for both BDD films. Comparing the highly and the lightly BDD electrode, higher deposition rate was observed in the highly doped electrode. This result can be attributed to the better conductivity of this electrode due to its higher boron content. It is noteworthy that the sensitization and activation processes are a crucial step for high quality coatings independently of the BDD doping level. Acknowledgments: Brazilian National Institute of Science and Technology (INCT) for Climate Change funded by CNPq Grant Number 573797/2008-0 e FAPESP Grant Number 2008/57719-9.

Tribological, anti-corrosive properties and biocompatibility of the micro- and nano-crystalline diamond coated Ti6Al4V

Diamond coatings may provide a way to strengthen the stability of the titanium abutment screw in dentistry for improving its lifespan. Microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films were deposited on Ti6Al4V (TC4) by hot-filament-assisted chemical vapor deposition (HFCVD). The morphology and quality of the diamond films were evaluated by SEM, AFM and Raman spectroscopy, respectively. Friction and corrosion experiments of MCD, NCD coated and uncoated TC4 samples were conducted in artificial saliva. The results indicate that diamond coating lowers the friction coefficient from 0.28 on TC4 to 0.2 on MCD and 0.1 on NCD. They also promote the corrosion resistance, in which NCD films present more efficient improvements. Cell proliferation (mitochondrial function, CCK-8 assay), the pattern of cell growth and cell apoptosis with L929 fibroblast cell culture systems proved that both MCD and NCD films provide suitable and cytotoxicity-free surfaces.

Specific Surface Area of Carbon Fine Particles Including Single-Walled Carbon Nanotubes Synthesized by Hot-Filament Plasma Assisted Chemical Vapor Deposition

ABSTRACTCarbon fine particles including single-walled carbon nanotubes (SWNTs) were synthesized by hot-filament and plasma assisted chemical vapor deposition. Specific surface area was evaluated for carbon fine particles synthesized under optimized conditions along with purified SWNTs and multi-walled carbon nanotubes (MWNTs) for comparison. The value of specific surface area for the synthesized carbon fine particles was smaller than the SWNTs, but larger than the MWNTs. Pore size distribution was analyzed with desorption isotherms by the DH method. Although smaller pores are included in the purified SWNTs than the synthesized carbon fine particles, pores of size larger than several nm were included more in the synthesized carbon fine particles.

Effects of temperature and Mo2C layer on stress and structural properties in CVD diamond film grown on Mo foil

Polycrystalline diamond films have been prepared by hot-filament-assisted chemical vapor deposition (HFCVD) on Mo foils. The morphology, growth rate, phase composition, element distribution and residual stress of the films at different temperature were investigated by field-emission scanning electron microscopy, Raman spectrum, field emission electron probe microanalysis and X-ray diffraction. Results show that the residual stress of the diamond films is compressive. The thermal stress plays a decisive role in the total stress, while the intrinsic stress can change the trend of the total stress. The residual stress of substrate gradually changes from tensile stress to compressive stress with the increase of the deposited temperature. A Mo2C interlayer is formed during deposition process, and this layer has an important influence on the stresses of films and substrates.

Porous Alumina Template based Versatile and Controllable Direct Synthesis of Silicon nanowires

ABSTRACTHighly densely packed, self-organized silicon nanowires with very narrow diameter distribution were synthesized within porous anodic alumina templates with electrodeposited catalytic metal nanoparticles. For successful catalytic metal nanoparticle deposition, electrochemical-, and chemical barrier layer thinning process was investigated following anodization process. Controlled pulsed electrodeposition process was carried out for a volume calibration of desired catalytic metal nanoparticle deposition inside nanopore arrays using different metal-ion containing electrolyte. Not only single metal nanoparticles, but also multi metal nanoparticles layers were filled inside PAA to enhance metal filling aspect, and to control the volume of nanoparticles more precisely. Using multilayered metal nanoparticles resulted on different SiNW’s growth behavior depending on the types of underlying metal nanoparticles.SiNWs were successfully synthesized using hot-filament assisted chemical vapor deposition system. Although silicon precursor gas can generally be dissociated at relatively low temperatures, the use of a hot filament activation help decreasing process temperature, and also, highly activated atomic hydrogen generation via the tungsten hot filament placed at gas inlet helps preventing parasitic amorphous silicon deposition on either the alumina membrane surface or the pore wall which hinders appropriate growth of SiNWs in PAA by nanopores clogging. Such densely packed, self-organized SiNWs are of high interest in many application fields like nanoelectronics, optoelectronics, and energy storage/conversion devices etc.

Effects of hydrogen etching process on the structural and optical properties of nano-crystalline diamond films

In this work, hydrogen etching method is applied to improve the quality of nano-crystalline diamond (NCD) films grown from hot-filament assisted chemical vapor deposition (HFCVD) system. From the characteristics of the structure and optical property, the grain size and surface roughness decrease while the optical transmission increase obviously under certain deposition parameters (gas pressure and substrate temperature) and longer etching time. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmittance reaches 53.3% at X-ray photon energy of 258eV, which has met the requirement for X-ray mask materials.

High-quality single-walled carbon nanotubes synthesis by hot filament CVD on Ru nanoparticle catalyst

We investigated the single-walled carbon nanotubes (SWCNTs) growth on Ru nanoparticle catalyst via hot filament assisted chemical vapor deposition (HFCVD) with two independent W filaments for the carbon precursor (methane) and the hydrogen dissociation respectively. The Ru nanoparticles were obtained following a two-step strategy. At first the growth substrate is functionalized by silanisation, then a self assembly of a ruthenium porphyrin complex monolayer on pyridine-functionalized metal oxide substrates. We have studied the impact of the filaments power and we optimized the SWCNTs growth temperature. The as grown SWCNTs were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. It was found that the quality, density and the diameter of SWCNTs depends on the filament and growth temperature. Results of this study can be used to improve the understanding of the growth of SWCNTs by HFCVD.

Laterally organized carbon nanotube arrays based on hot-filament chemical vapor deposition

Lateral porous anodic alumina (PAA) templates were used to organize carbon nanotubes (CNTs) grown by a hot-filament assisted chemical vapor deposition (HFCVD) process. For the CNT growth, we used a modified “home-made” HFCVD system with two independently powered filaments which are fitted respectively on the methane (CH 4) gas line, which serves as a carbon precursor and on the hydrogen (H 2) gas line, which acts as an etching agent for the parasitic amorphous carbon. Various activation powers of the hot filaments were used to directly or indirectly decompose the gas mixtures at relatively low substrate temperatures. A parametric study of the HFCVD process has been carried out for optimizing the confined CNTs growth inside the lateral PAA templates.

Development and Characterization of a Diamond-Based Localized Surface Plasmon Resonance Interface

The paper reports on the fabrication of a localized surface plasmon resonance (LSPR) interface with nanocrystalline diamond (NCD) as overcoating. The LSPR interface is formed through thermal evaporation of a 4 nm gold film onto quartz substrates and postannealed at 800 °C. The resulting gold nanostructures (Au NSs) are further coated with nanocrystalline diamond (NCD) films produced by hot filament-assisted chemical vapor deposition (HFCVD) at 800 °C. The influence of the NCD film thickness on the wavelength at maximum absorption (λmax) was investigated by recording UV−vis transmission spectra in air. The experimentally obtained data were compared to the theoretically calculated one. The possibility to introduce chemical functions on the quartz/Au NSs/NCD interfaces was demonstrated by (i) photochemical oxidation of the NCD overcoating and subsequent reaction of the oxidized surface with perfluorodecyltrichlorosilane or (ii) chemical linking of the 4-nitrobenzene diazonium salt directly onto as-grown hydrogen-terminated NCD films.

Diamond deposition on siliconized stainless steel

Silicon diffusion layers in AISI 304 and AISI 316 type stainless steels were investigated as an alternative to surface barrier coatings for diamond film growth. Uniform 2 μm thick silicon rich interlayers were obtained by coating the surface of the steels with silicon and performing diffusion treatments at 800 °C. Adherent diamond films with low sp 2 carbon content were deposited on the diffused silicon layers by a modified hot filament assisted chemical vapor deposition (HFCVD) method. Characterization of as-siliconized layers and diamond coatings was performed by energy dispersive X-ray analysis, scanning electron microscopy, X-ray diffraction and Raman spectroscopy.

Evaluation of Silicon Nitride Ceramic Cutting Tools with Diamond Coatings

There is a substantial increase on carbon-carbon composites use for engineering applications, considering its high temperature properties and low specific mass. However the machining costs are relatively high, and new cutting tools, mainly ceramics, must be developed to overcome such difficulty, aiming cost reductions. In this work, silicon nitride based ceramics has been prepared , by pressureless sintering of silicon nitride powders and appropriate amounts of Al2O3,Ce2O3, Y2O3 and AlN. Cutting tools were prepared from the sintered materials, with geometry according to ISO1832. Selected cutting tools were also diamond coated by a hot filament-assisted Chemical Vapor Deposition (HFCVD) diamond coating process. Carbon Fiber Reinforced Carbon (CFRP) composites machining was performed, to evaluate the diamond coating influence on machining performance. After the tests, the uncoated tools presented severe flank wear and shorter life than the diamond coated ceramic tools. This flank wear is caused by the abrasive carbon powder generated during the facing operation. On CVD diamond coated α-SiAlON ceramic tools, no flank wear was observed, and the cutting edge remained unmodified, even for severe test conditions, such as high cutting length and speed. Carbon particles, originated from the machined composite, do not promotes diamond film rupture, but instead, acts as lubricant film and reduces composite surface initial roughness.

Characterization of boron doped nanocrystalline diamonds

Nanostructured diamond doped with boron was prepared using a hot-filament assisted chemical vapour deposition system fed with an ethyl alcohol, hydrogen and argon mixture. The reduction of the diamond grains to the nanoscale was produced by secondary nucleation and defects induced by argon and boron atoms via surface reactions during chemical vapour deposition. Raman measurements show that the samples are nanodiamonds embedded in a matrix of graphite and disordered carbon grains, while morphological investigations using field electron scanning microscopy show that the size of the grains ranges from 20 to 100 nm. The lowest threshold fields achieved were in the 1.6 to 2.4 V/μm range.

Effect of Boron Concentration on Adhesion and Cutting Performance of Diamond-Coated Cemented Carbide Tools

Diamond thin films doped with various boron concentrations were grown on WC-Co cemented carbide tools by hot-filament-assisted chemical vapor deposition (HFCVD). The trimethyl borate dissolved in acetone solution was used as the boron resource (B/C=0%, 0.1%, 0.3%, 0.5%). The surface morphology of diamond films with different boron contents was investigated by Scanning electron microscopy, the adhesive strength was calculated by means of indentation test under a load of 1500N. A real cutting performance was carried out on Al metal matrix composites material (20vol%SiC, 15μm), and the insert flank wear was examined by measuring the scars that appeared on the cutting edge with tool microscope. The research results shown the surface morphology and structure of the diamond films changed owing to boron doping. As the doping levels increased, the average grain size of the films decreased from 10 to 2μm. A significant improvement in adhesion and cutting performance were observed as the boron contents increased from 0% to 0.5%. The adhesion and cutting performance were best when the boron concentration was 0.3%. Adequate boron can effectively suppress the cobalt diffusion to the substrate surface and avoid the catalytic effect of cobalt at the high temperature. It is of great significance for improvement of the adhesive strength and cutting performance of diamond-coated tools using above method.

Growth of nanodiamond/carbon-nanotube composites with hot filament chemical vapor deposition

The growth of diamond/carbon-nanotube (CNT) composites by Hot Filament Assisted Chemical Vapor Deposition (HFCVD) was investigated. The growth was achieved by pre-dispersing commercially available multiwalled CNTs onto a Si(100) surface and subsequently growing diamond nanoparticles over this layer. The diamond/CNT composites were characterized with SEM, TEM, and Raman Spectroscopy. It was found that in a flow of 1% CH 4 in H 2 (a typical condition for microcrystalline diamond growth using HFCVD) most of the CNTs are destroyed by the harsh growth conditions. Reduction in the etching of the CNTs was achieved by reducing the H 2 partial pressure in the precursor flow. There exists an optimal between 2–5% of CH 4 in H 2 wherein the CNTs are not destroyed and the resulting diamond film retains a high percentage of its sp 3 structure. The TEM analyses showed that nanometer sized diamond particles nucleate on the surface of the CNTs and grow radially outward. The retention of the CNT structure and the direct growth of the diamond on the CNTs, the two factors necessary for good load transfer between a matrix and reinforcement, suggest the possibility of using this material as a structural composite. Based on the characterization of the composite, a growth mechanism for diamond onto the CNTs was proposed.

Field-emission properties of sulphur doped nanocrystalline diamonds

Nanostructured diamond doped with sulphur has been prepared using a hot-filament assisted chemical vapour deposition system fed with an ethyl alcohol, carbon disulfide, hydrogen, and argon mixture. The reduction of diamond grains to the nanoscale is relevant to create a network of defective grain boundaries which may be n-type doped to facilitate the transport and injection of electrons to the diamond grains located at the vacuum interface, enhancing the electron field-emission properties of the samples. The downsizing was produced by secondary nucleation and defects induced by sulphur and argon atoms in the chemical vapour deposition surface reactions. Sulphur also acts as an n-type dopant of diamond. Raman measurements show that the samples are nanodiamonds embedded in a matrix of graphite and disordered carbon grains and the morphology, revealed by field electron scanning microscopy, shows that the grains are in the range of 10 to 30 nm. The lowest threshold achieved for field emission was 13.20 V/μm.