Hot Filament Chemical Vapor Deposition Research Articles

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.

Temperature-dependent residual stress and thermal stability studies of multilayer HF-CVD diamond coatings on RB-SiC

Structurally graded multilayer (ML) diamond coatings were deposited on reaction bonded silicon carbide (RB-SiC) using a hot filament chemical vapour deposition (HF-CVD) system via two different routes: a continuous process (C-ML) and a three-step intermittent process (Ix-ML, x being the number of steps). In this study, the temperature-dependent residual stresses and thermal stabilities of the C-ML and Ix-ML coatings after annealing at 100° intervals from 100 °C–800 °C were investigated. Scanning electron microscopy, 2D/3D Raman mapping, cluster analysis, and sp2/sp3 ratio computations were carried out at all stages and the results were compared. The residual stresses of the as-deposited coatings, I1-ML, I2-ML, I3-ML, and C-ML, were compressive with values of −1.09 GPa, −0.90 GPa, −0.62 GPa and −1.35 GPa, respectively, which progressively shifted to the tensile regime on annealing and exhibited values of 0.50 GPa, 0.50 GPa, 0.61 GPa and 1.75 GPa respectively, after annealing at 700 °C. The sp2/sp3 ratios of the C-ML and I3-ML coatings dropped from 0.94% to 0.54% and 1.07% to 0.54%, respectively, as the annealing temperature increased from 100 °C to 700 °C. All coatings were completely oxidised at 800 °C except I3-ML, where patches of the original coating persisted even after annealing at 800 °C.

MIS-Like Structures with Silicon-Rich Oxide Films Obtained by HFCVD: Their Response as Photodetectors.

MIS-type structures composed of silicon-rich oxide (SRO), thin films deposited by hot filament chemical vapor deposition (HFCVD), show interesting I-V and I-t properties under white light illumination and a response as photodetectors. From electrical measurements, it was found that at a reverse bias of −4 V, the illumination current increased by up to three orders of magnitude relative to the dark current, which was about 82 nA, while the photogenerated current reached a value of 25 μA. The reported MIS structure with SRO as the dielectric layer exhibited a hopping conduction mechanism, and an ohmic conduction mechanism was found with low voltage. I-t measurements confirmed the increased photogenerated current. Furthermore, the MIS structure, characterized by current-wavelength (I-λ) measurements, exhibited a maximum responsivity value at 254 mA/W, specific detectivity (D*) at 2.21 × 1011 cm Hz1/2 W−1, and a noise equivalent power (NEP) of 49 pW at a wavelength of 535 nm. The structure exhibited good switching behavior, with rise and fall times between 120 and 150 ms, respectively. These rise and decay times explain the generation and recombination of charge carriers and the trapping and release of traps, respectively. These results make MIS-type structures useful as photodetectors in the 420 to 590 nm range.

Duo Emission of CVD Nanodiamonds Doped by SiV and GeV Color Centers: Effects of Growth Conditions.

The investigation of the hot filament chemical vapor deposition nanodiamonds with simultaneously embedded luminescent GeV− and SiV− color centers from solid sources showed that both the absolute and relative intensities of their zero-phonon lines (at 602 and 738 nm) depend on nanodiamond growth conditions (a methane concentration in the CH4/H2 gas mixture, growth temperature, and time). It is shown that a controlled choice of parameters of hot filament chemical vapor deposition synthesis makes it possible to select the optimal synthesis conditions for tailoring bicolor fluorescence nanodiamond labels for imaging biological systems.

Electrochemical properties and morphology of boron-doped diamond thin films

A boron-doped diamond (BDD) thin film was synthesized using the hot filament chemical vapor deposition (HFCVD) method. The surface shape, growth rate, bonding structure, and electrochemical properties of the BDD thin films were estimated through scanning electron microscopy (SEM), Raman spectroscopy, and cyclic voltammetry. As the boron doping concentration increased, the growth rate and crystal size of the diamond thin film decreased. Through Raman analysis, it was confirmed that the 1332 cm[Formula: see text] peak of diamond gradually became less intense, and peaks were generated at 480 cm[Formula: see text] and 1220 cm[Formula: see text] due to the bonding of boron to carbon. Cyclic voltammetry analysis of the BDD thin film showed a large potential window with a width of approximately 2.8 V. The highest applied voltage (2 V) versus response current (0.02 A) was obtained at a B/C ratio of 2000 ppm.

Fabrication and grinding performance of CVD diamond abrasive tool

The chemical vapor deposition (CVD) method has become a new choice for the fabrication of diamond grinding tools with excellent wear resistance. Different diamond abrasive particles were deposited on the lapping and sandblasting pretreated silicon nitride ceramic substrate by hot filament chemical vapor deposition (HFCVD) method to fabricate CVD diamond abrasive tools. To analyze the influence of pretreatment methods on adhesion strength, the micromorphology, surface roughness, Raman stress, and Rockwell indentation of CVD diamond abrasive tools with different parameters were characterized. Meanwhile, grinding tests on cemented carbide wire drawing dies were carried out, and the grinding performance of different abrasive particles was evaluated. The results show that sandblasting pretreatment can increase the matrix surface roughness, accelerate the growth of diamond abrasive particles and improve the adhesion between the abrasive layer and substrate, and the CVD diamond grinding tool with sandblasting pretreatment substrate and coarse particle has the best dust removal ability and the longest grinding life. The cemented carbide grinding tests of the CVD diamond grinding tool and electroplated diamond grinding tool with the same particle size are processed and compared, it shows that the grinding life of the CVD diamond grinding tool is longer, and the surface roughness value of the workpiece is lower than that of the electroplated diamond grinding tool.

Study of horizontal and vertical uniformity of B-doped layer on mosaic single crystal diamond wafers by using hot-filament chemical vapor deposition

Aiming at developing inch-sized processing of diamond, B-doped layer was grown on mosaic single-crystallin diamond wafers by using hot-filament chemical vapor deposition (CVD), which is expected to have an advantage in terms of the deposition area compared with microwave plasma (MWP) CVD. Uniformity in horizontal and vertical directions is studied. It is found that the junctions of the monocrystalline diamond domains in the mosaic wafer and the direction of the crystal off-angles against to these junctions are less effective to the uniformity of the impurity concentrations. On the other hand, it is suggested that excess incorporation of W from the filament suppresses the growth and incorporation of B. It is shown that millimeter scale or more precise control of the arrangement of the wafer and the filament enables to obtain more uniform and efficient doping.

Near Room-Temperature Synthesis of Vertical Graphene Nanowalls on Dielectrics.

Vertical graphene nanowalls (VGNs) with excellent heat-transfer properties are promising to be applied in the thermal management of electronic devices. However, high growth temperature makes VGNs unable to be directly prepared on semiconductors and polymers, which limits the practical application of VGNs. In this work, the near room-temperature growth of VGNs was realized by utilizing the hot filament chemical vapor deposition method. Catalytic tantalum (Ta) filaments promote the decomposition of acetylene at ∼1600 °C. Density functional theory calculations proved that C2H* was the main active carbon cluster during VGN growth. The restricted diffusion of C2H* clusters induced the vertical growth of graphene nanoflakes on various substrates below 150 °C. The direct growth of VGNs successfully realized the excellent interfacial contact, and the thermal contact resistance could reach 3.39 × 10-9 m2·K·W-1. The temperature of electronic chips had a 6.7 °C reduction by utilizing directly prepared VGNs instead of thermal conductive tape as thermal-interface materials, indicating the great potential of VGNs to be directly prepared on electronic devices for thermal management.

Lapping performance of diamond cone array tool prepared by double bias assisted HFCVD

In this paper, the free-standing diamond (FSD) and microcrystalline diamond (MCD) film were etched by double-bias assisted hot filament chemical vapor deposition (HFCVD) to prepare two kinds of diamond cone array tools (DCATs) for precision processing. It is the first time to use free-standing diamond cone array tool (FSD-CAT) and microcrystalline diamond cone array tool (MCD-CAT) to perform the lapping processing experiment for monocrystalline silicon and to carry out the performance evaluation of DCAT. The surface roughness of the silicon lapped by FSD-CAT is 28.9 nm, and the surface roughness of the silicon lapped by MCD-CAT is 18 nm. By using the combination of both DCATs to lapped silicon, a smooth surface with a surface roughness of 5 nm is obtained. By comparing the surface roughness of monocrystalline silicon which lapped by diamond tools with and without etching, because of the smaller cross-section of the cones cut into the surface of monocrystalline silicon, DCAT can effectively reduce the Surface roughness of the silicon.

Effect of extreme mechanical densification on the electrical properties of carbon nanotube micro-yarns

We have explored the effect of high pressure post-treatment in optimizing the properties of carbon nanotube yarns and found that the application of dry hydrostatic pressure reduces porosity and enhances electrical properties. The CNT yarns were prepared by the dry-spinning method directly from CNT arrays made by the hot filament chemical vapour deposition (HF-CVD) process. Mechanical hydrostatic pressure up to 360 MPa induces a decrease in yarn resistivity between 3% and 35%, associated with the sample’s permanent densification, with CNT yarn diameter reduction of 10%–25%. However, when increasing the pressure in the 1–3 GPa domain in non-hydrostatic conditions, the recovered samples show lower electrical conductivity. This might be due to concomitant macroscopic effects such as increased twists and damage to the yarn shown by SEM imaging (caused by strong shear stresses and friction) or by the collapse of the CNTs indicated by in situ high pressure Raman spectroscopy data.

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

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

Porous boron-doped diamond for efficient electrocatalytic elimination of azo dye Orange G

Boron-doped diamond (BDD) is an ideal material being used for electrocatalytic elimination of environmental organic pollutants, but the commercial BDD electrodes have several limitations such as small electroactive area, slow mass transfer and low pollutants decomposition efficiency. In this paper, porous BDD electrodes with different pore sizes were synthesized by replicating porous Ti (powder metallurgy) with three-dimensional interoperable network structure, controllable aperture and porosity in a hot filament chemical vapor deposition (HFCVD) system. Various aspects of porous BDD with different pore sizes in terms of physicochemical properties, electrocatalytic reaction kinetics and mass transfer, which had not been previously researched, were systematically discussed. Meanwhile, some fundamental issues such as the enhancement mechanism of reaction kinetics of porous electrodes, the electrocatalytic degradation mechanism and pathways of contaminants on flat and porous BDD electrodes have been thoroughly investigated. Porous BDD electrodes had significantly higher Orange G (OG) electrocatalytic apparent reaction rate constants (up to 5.55 times that with flat BDD) and dramatically lower electrical energy per order (down to 25% that with flat BDD) for pollutant removal due to their increased electroactive area, reduced charge transfer resistance, and enhanced mass transfer. The electroanalysis, hydroxyl radical quenching and intermediates identification revealed the electrocatalytic degradation mechanism and reaction pathways of OG. In general, Porous BDD electrodes combined the properties of BDD and porous Ti, making them a commercially applicable and efficient material with high electroactive area, high electrocatalytic activity, long-term stability and low cost for electrocatalytic elimination of environmental organic pollutants.

Integration of 3D interconnected porous microstructure and high electrochemical property for boron-doped diamond by facile strategy

• A new template-free approach for constructing porous BDD films is presented. • Integration of high-quality diamond and unique 3D interconnected porous microstructure is achieved. • 3D porous BDD film exhibits high electrochemical response, wide potential window and large double layer capacitance. • Relationship between electrochemical behavior and microstructure is discussed. Three-dimensional (3D) porous boron-doped diamond (BDD) film is an attractive electrode material but tough to synthesize. Herein, the 3D porous BDD films were constructed in a facile and template-free way. The BDD/non-diamond carbon (NDC) composite films were firstly fabricated by hot filament chemical vapor deposition (HFCVD) technique, and then the porous BDD films with 3D interconnected porous microstructure, different pore size and NDC-free diamond were achieved by selective removal of NDC. It is manifested that higher electrochemical response, large double layer capacitance (17.54 mF/cm 2 ) in diamond electrodes, wide electrochemical window of 2.6 V and superior long-term stability were achieved for 3D porous BDD film. This derives from the synergistic effect of microstructure and phase composition of the porous films. 3D interconnected structure possesses prominent improvement of effective surface area and accessible porous channel, significantly enhancing the species adsorption and mass transfer. The 3D porous BDD films, composed of NDC-free diamond, exhibit excellent structural stability and corrosion resistance, which favor the enhancement of long-term stability and water splitting overpotential. The facile fabricating approach and excellent structure/electrochemical character demonstrate the appealing application in many electrochemical fields for 3D porous BDD films, such as energy storage and conversion, wastewater treatment and purification. The electrochemical performance of boron-doped diamond (BDD) film is improved significantly through constructing three-dimensional interconnected porous microstructure with high-quality diamond, which is synthesized facilely by deposition of BDD/non-diamond carbon (NDC) composite film and selectively removing NDC.

Research on the innovative pretreatment to improve the adhesion and performance of diamond coatings

In order to improve the quality of diamond coatings, this paper combined the chemical etching and buffer layers to deal with cemented carbide with cobalt (Co) content of 8%. Diamond coatings were prepared with hot filament chemical vapor deposition (HFCVD). The surface morphology, quality and wear property were explored by using scanning electron microscopy, X-ray diffraction, laser Raman spectrometer, and friction and wear tester. Compared to the sample with no pretreatment, samples after pretreatment have better surface morphology. There are no obvious impurities as well. Diamond crystals are uniform and compact. Friction and wear test indicated that the friction coefficient is lower than 0.1. Samples after pretreatment are much lower and steady among them. The sample using tungsten(W)-molybdenum(Mo) layer has the best surface morphology and the lowest friction coefficient. The result shows that the pretreatment combined the chemical etching and buffer layers cannot only act as the diffusion barrier, but also can improve the adhesion between substrate and diamond coatings. The effect of composite buffer layer is better than single metal buffer layers.

Effect of carbon concentration on optical and structural properties in the transition from Silicon Rich Oxide to SiCxOy films formation

The role of carbon atomic concentration on the transition from Silicon Rich Oxide (SRO) to Silicon Oxicarbide films (SiCxOy) is reported. For this, optical and structural properties were analyzed by Photoluminescence (PL), Micro-Raman, Fourier Transform Infrared (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) measurements. An SRO film with 16.6 at.% of Si-excess and SiCxOy films with carbon concentration from 1.3 to 7.2 at.% were grown by Hot Filament Chemical Vapor Deposition Technique (HFCVD). The SRO film (C = 0 at.%) and SiCxOy films with low carbon atomic concentration (C = 1.3 at.%) exhibited a very low PL emission in the red-infrared region (1.5–1.7 eV) manly attributed to SiO defects which are reduced or annihilated by incorporation of carbon. An increase in carbon atomic concentration greater than 1.3 produces a strong PL emission at white region (3.35–1.72 eV) characteristic of SiCxOy films attributed to radiative defects such as defects associated to Si-related oxygen vacancies (Si-NOVs), Si-related oxygen deficiency centers (Si-ODC) and C-related oxygen vacancies (C-NOVs). In this work it was found that a carbon atomic concentration greater that 1.3 is required to have a high density of these radiative defects. Also, due to the high growth temperature (900 °C) and Si-excess (from 16.6 to 3.9 at.%), we propose the presence of Si nanocrystals (Si–NCs) embedded in both SRO and SiCxOy films with low carbon concentration (SiO2-Like characteristics). Whereas an increase in carbon concentration of 7.2 at. %, Si–NCs precipitation was inhibited in the SiCxOy films.

Tribological Performance of Diamond Films with Different Roughnesses of Silicon Nitride Substrates and Carbon Source Concentrations.

Diamond films were deposited on silicon nitride (Si3N4) substrates with three different roughnesses using the method of hot-filament chemical vapor deposition (HFCVD). The tribological properties of the film were studied by changing the deposition time, deposition distance, and methane (CH4) concentration. The friction coefficient, delamination threshold load, and wear rate of the diamond films were tested and calculated using the reciprocating friction and wear test under dry friction conditions. The results show that, when the deposition time is 12 h, the bonding force of the film is the lowest and the friction coefficient is the largest (0.175, 0.438, and 0.342); the deposition distance has little effect on the friction performance. The friction coefficients (0.064, 0.107, and 0.093) of nano-diamond films (NCD) prepared at a 40 sccm CH4 concentration are smaller than those of micro-diamond films (MCD) prepared at a 16 sccm CH4 concentration. The load thresholds before delamination of Ra 0.4 μm substrate diamond film are as high as 40 N and 80 N, whereas the diamond films deposited on Ra 0.03 μm substrates have lower wear rates (4.68 × 10−4 mm3/mN, 5.34 × 10−4 mm3/mN) and low friction coefficients (0.119, 0.074, 0.175, and 0.064). Within a certain load range, the deposition of a diamond film on a Ra 0.03 μm Si3N4 substrate significantly reduces the friction coefficient and improves wear resistance. Diamond film can improve the friction performance of a workpiece and prolong its service life.

Synthesis of diamond crystal growth on tungsten carbide inserts by HFCVD using various seeding powders.

The hot filament chemical vapor deposition (HFCVD) process is used to synthesize diamond crystals on cemented carbide (WC–Co) SPUN inserts. Diamond (Dia.), carbon (GC-glassy spherical form), iridium (Ir), molybdenum (Mo), palladium (Pd), platinum (Pt), tungsten (W), and tantalum (Ta) powders were used as seeding materials for crystal growth. Scanning electron microscopy (SEM) data revealed the development of a few diamond crystals in platinum, iridium, and tungsten powders. The seeding with carbon, tantalum, and diamond powders formed clustered microcrystalline diamond (MCD) crystals, although other powders produced discrete crystals. Tantalum and diamond-seeded powders produced the most significant number and size of crystals. According to micro-Raman spectroscopy (µ-RS), tantalum powder had the lowest ID/IG ratio and the most excellent sp3 bonding. X-ray diffraction (XRD) revealed the maximum diamond intensity in the (111) plane. According to atomic force microscopy (AFM), diamond and molybdenum powders had the largest grains, whereas tantalum powder had the smallest root mean square roughness value with a homogeneous grain distribution. The Vickers microhardness (VHN) test confirmed the highest hardness value for diamond and tantalum seeded powder coatings with the least amount of radial cracking. Field emission scanning electron microscopy (FESEM) revealed that both powders had higher film thickness values.

Quasi-saturation dependent wear resistance of nanocrystalline diamond films under heavy-ion irradiation with large displacement damage

Here two groups of experimental studies were performed to investigate the irradiation hardness and tribological performance of nanocrystalline diamond (NCD) films synthesized using hot-filament chemical vapor deposition. Extensive characterizations including the Raman, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy were applied, to explore the structural and property evolution of heavy-ion radiated films with a gradual increase of the displacement damage. Results indicated that films with different original structures possessed the same starting point of a quasi-saturation state at 2.0 dpa, above which films underwent a significant transformation from the sp3 to sp2 bonds within the depth of the projected range, forming an amorphous layer with an identical bonding structure among the different samples. The radiation-induced amorphization resulted in a change in the wear mechanism in dry sliding movements, i.e., from the abrasive wear in the pristine films to the adhesive wear in the radiated films. Furthermore, a formation of graphene nanocrystals was observed in the wear scars of radiated films, which favored the stability of friction coefficient curves. As the displacement damage further increased to 5.0 and 10.0 dpa, the bonding structure of the amorphous layer was well maintained, and in the meantime, the low-friction characteristics of the radiated films were also well maintained, even as the tribotests were continued for 5 × 105 laps and the wear depth had already exceeded the projected range of incident ions. Furthermore, the larger the irradiation damage, the greater the graphitization transformation occurring in the tribofilms, and the lower the film wear rates in an ambient air atmosphere. These results provide insights into what changes in the film nanostructures and sliding interfaces are responsible for the ultrahigh wear resistance of NCD films under nuclear irradiation conditions with large displacement damage.

Novel approach to synthesize morphology variant tungsten oxide thin films for efficient chemical sensing

A new approach has been designed to synthesize and modify the morphology of high quality nanocrystalline tungsten oxide (WO3) thin films using hot filament chemical vapor deposition (HFCVD) technique. The thin films were successfully synthesized having completely distinct morphologies using different processing conditions in very short duration of time 4–6 min. Two types of morphologies resembling a broccoli decorated with WO3 nanograins (BWN) and another having faceted, pyramidal growth of WO3 nanograins (PWN) were obtained. Both as-prepared films displayed excellent uniformity and exhibited the formation of standard monoclinic structure without undergoing any additional calcination/sintering. The morphology variant WO3 thin films were applied as sensing electrodes to detect toxic chemical such as diethylamine (DEA) chemical. Due to smaller particle size, higher surface area and higher oxygen contents, the BWN thin film offered promising performance in DEA sensing with good sensitivity of ∼3.5 μAμM−1cm−2 and fast response ∼10 s.

Characterization of mosaic diamond wafers and hot-filament epilayers by using HR-EBSD technics

Tungsten (W) incorporated diamond film was homoepitaxially grown on a mosaic diamond wafer by hot-filament chemical vapor deposition. The crystallinity of the W incorporated epilayer and the original mosaic diamond wafer was characterized by using high-resolution electron backscatter diffraction (HR-EBSD). From kernel average misorientation maps (KAM) derived from HR-EBSD measurements, it was found that the numerical value of KAM and the width of coalescence boundary region (CBR) of W incorporated epilayers were much smaller than those of original mosaic diamond wafers and not only in the CBR but also in the bulk area, the crystalline quality of the W incorporated epilayer is better than that of the original mosaic diamond wafers. It is suggested that the primal role for the W incorporation is strain reduction near threading dislocations during growth.