Filament Chemical Vapor Deposition System Research Articles

Preparation of nanodiamonds based on phase transformation of vertical sheet under atmospheric pressure

A basic and important way to prepare diamond is to make graphite experience the phase transformation under the high-pressure high-temperature (HPHT) condition. However, this method needs stringent equipment and high investment cost. Recently, we proposed a method to prepare the diamond by phase transformation of graphite at atmospheric pressure with monodispersed Ta atoms. It is found that a phase transformation happens to H atoms under atmospheric pressure, but the role of O atoms has not been investigated. Here, we use tantalum wires as Ta source and heat the filaments to prepare vertical graphene containing Ta atoms in hot filament chemical vapor deposition (HFCVD) system. And then the vertical graphene layers are annealed in oxygen-containing environment, and nanodiamonds are obtained by phase transformation from the vertical graphene under atmospheric pressure. The results show that the sample morphologies are the same as the untreated vertical graphene’s, when the annealed ambient air pressure is at 10 Pa and 50 Pa with oxygen atom content of 1.96% and 2.04%, respectively; TEM tests reveal TaC and graphite but no diamond in these samples . Nanodiamond grains with the size range of 2–4 nm are observed in the amorphous carbon region of samples annealed at 100 Pa and 500 Pa air pressure with oxygen atom content increasing to 2.77% and 3.11%, respectively, indicating that oxidation facilitates the phase change from Ta-containing vertical graphene to diamond at atmospheric pressure. When the air pressure of the annealing environment rises to 1000 Pa with the oxygen atom content of 3.54%, the sample is extensively oxidized and the graphite structure is severely damaged,which means that a large number of oxygen atoms tend to disrupt the graphite structure rather than promote the phase change into diamond. These results supply a way to prepare nanodiamond and show the effect of O atoms in the graphite phase transition at atmospheric pressure.

Ordinary-pressure phase transition from graphite to diamond induced by monodispersed Ta atoms

High pressure high temperature (HPHT) was conventionally required for the phase transition from graphite to diamond. Here, we deposited monodispersed Ta atoms on pressed pure graphite substrate in hot filament chemical vapor deposition system and then performed annealing on the sample under ordinary pressure, letting graphite transit to diamond. Specifically, along the longitudinal direction the unannealed sample is divided into three regions of TaC particles, amorphous carbon and graphite, and 2–3 nm sized diamond grains are only observed among the TaC particles. After annealing the sample under 1000 °C for 15 min, diamond grains not only form among TaC particles, but also appear in amorphous carbon region. It is observed that more diamond grains with larger size of 3–10 nm and diamond variant structures i-Carbon (i-C) with the size larger than 30 nm are formed in amorphous carbon region. And more monodispersed Ta atoms are distributed in the amorphous carbon region of the annealed sample. This suggests that monodispersed Ta atoms firstly change graphite into amorphous carbon and then induce its transformation into i-C and diamond. Our results give a different way from HPHT method to prepare diamond based on graphite under ordinary pressure.

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.

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.

Tailored structure and photoluminescence of substoichiometric molybdenum oxide nanomaterials by doping of gallium oxide

Substoichiometric molybdenum oxide (MoO 3- x ) nanomaterials become the promising structure-dependent semiconductor materials. However, the structural tuning of MoO 3- x nanomaterials is still an important challenge. Here we report the tuned MoO 3- x nanostructures via the doping of Ga 2 O 3 in hot filament chemical vapor deposition system. The diverse characterization results indicate that the addition of Ga 2 O 3 in the MoO 3 precursor leads to the doping of Ga 2 O 3 in the MoO 3- x nanostructures and the increase of the MoO 2 component in MoO 3- x nanomaterials. Furthermore, the addition of Ga 2 O 3 improves the regularity of MoO 3- x nanoparticles (NPs) and induces the lattice expansion of MoO 3- x nanostructures. The photoluminescence (PL) properties were measured at room temperature. The PL results exhibit that the synthesized MoO 3- x nanomaterials generate the ultraviolet, blue, green, red and near infrared light due to the bandgap transition, the transition between two sub-bands, the intervalence charge transfer transition and the transition from the intermediate level to valence band, respectively. In addition, the PL results also reveal the PL quenching due to the doping of Ga 2 O 3 , which is related to the reduction of nanocavities, the aggregation of the MoO 3- x NPs and the increase of MoO 2 phase induced by the incorporation of Ga 2 O 3 in the MoO 3- x nanostructures. These achievements can contribute to the tuning of MoO 3 -based nanostructures and the development of next-generation optoelectronic nanodevices based on doping-engineered MoO 3 nanomaterials. • MoO 3- x nanomaterials with a low doping level of Ga 2 O 3 . • Tailored structures of MoO 3- x nanomaterials by doping of Ga 2 O 3 . • Tunable optical properties of Ga 2 O 3 -doped MoO 3- x nanomaterials.

Effect of heat treatment on electrical and surface properties of tungsten oxide thin films grown by HFCVD technique

The present research focuses on the synthesis, characterization, and electrical properties of tungsten oxide thin films deposited using the Hot filament chemical vapor deposition (HFCVD) system on stainless steel 316L substrate. Various characterization tools such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy were used to study the structural, morphological, and surface roughness of the samples. The obtained results from XRD demonstrated development of WO2 and WO3 phases and enhancement in the crystallinity upon an increase in the substrate temperature of tungsten oxide thin films. High substrate temperature also caused a low number of defects and dislocation density as well as low micro-strain values. According to SEM results, tungsten oxide thin films composed of closely packed uniform crystal clusters with an improvement in the grain size upon increasing substrate temperature. The acquired AFM images demonstrate increasing grain/cluster size on the surface of deposited thin films and decreasing surface roughness with rising substrate temperature. The Raman spectroscopy results illustrate five distinct stretching vibrational bands of O-W-O which are ascribed to W6+=O stretching mode of terminal oxygen atoms. The obtained results of electrical resistivity using four-probe method demonstrate that the resistivity of films decreases upon an increase in the grain size when the substrate temperature increases. This observation is consistent with the larger grain boundaries and scatter carriers which result in reduction of mobility. This paper provides a facile preparation of tungsten thin films useful for variety of optoelectronic, photovoltaic, and energy storage devices.

Structural and tribological properties of tungsten oxide thin film on a silicon substrate

In this work, tungsten oxide thin films are deposited on silicon substrates using the hot filament chemical vapor deposition system. The influence of substrate temperature on the structural, morphological, and elemental composition of the tungsten oxide thin films is investigated using X-ray diffraction, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy techniques. Also, the mechanical and tribological properties of these thin films are considered using nanoindentation and scratch tests. Based on X-ray diffraction results, it can be concluded that tungsten oxide thin films are synthesized with a cubic WO3 structure. From field-emission scanning electron microscopy images, it can be seen that tungsten oxide thin films are made of crystal clusters which have grown vertically on the substrate surface. In addition, the results exhibit two asymmetric W4d5/2 and W4d7/2 peaks which can be assigned to W5+ and W4+ species, respectively. The mechanical results show that the hardness and the elastic modulus increase on raising the substrate temperature up to 600 °C. From the tribological performances, the friction coefficient of the tungsten oxide thin film decreases on increasing the substrate temperature.

Influences of grain size and microstructure on optical properties of microcrystalline diamond films**Project supported by the Key Project of the National Natural Science Foundation of China (Grant No. U1809210), the National Natural Science Foundation of China (Grant Nos. 50972129 and 50602039), the International Science Technology Cooperation Program of China (Grant No. 2014DFR51160), the National Key Research and Development Program of

Microcrystalline diamond (MCD) films with different grain sizes ranging from 160 nm to 2200 nm are prepared by using a hot filament chemical vapor deposition (HFCVD) system, and the influences of grain size and structural features on optical properties are investigated. The results show that the film with grain size in a range of 160 nm–310 nm exhibits a higher refractive index in a range of (2.77–2.92). With grain size increasing to 620±300 nm, the refractive index shows a value between 2.39 and 2.47, approaching to that of natural diamond (2.37–2.55), and a lower extinction coefficient value between 0.08 and 0.77. When the grain size increases to 2200 nm, the value of refractive index increases to a value between 2.66 and 2.81, and the extinction coefficient increases to a value in a range of 0.22–1.28. Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located in a range of 1331 cm−1–1333 cm−1, the content of diamond phase increases gradually as grain size increases, and the amount of trans-polyacetylene (TPA) content decreases. Meanwhile, the sp2 carbon clusters content and its full-width-at-half-maximum (FWHM) value are significantly reduced in MCD film with a grain size of 620 nm, which is beneficial to the improvement of the optical properties of the films.

Adherent diamond coating deposited on Ti by ultrasonic after carbonization pretreatment

The adhesion of wear-resistant diamond coating deposited on titanium was weakened by the porous titanium carbide interlayer, which was formed before film growth. In order to enhance substrate-coating adherence, a new pretreatment method was presented: Ti substrates were carbonized by hot filament chemical vapor deposition system, and then the carbonized substrates were ultrasonically vibrated using diamond micro-powder suspension. Diamond coatings were deposited by hot filament chemical vapor deposition as well. The effect of carbonization time on adhesion was investigated. The carbonized substrates and the interface between diamond coatings and substrates were characterized. The results showed that as the carbonization time increases, porous structures and cracks appear and increase on the surface of the substrate. The carbonized substrates possess high surface energy and thus the nucleation is promoted. After deposition, a dense and thin titanium carbide was observed. Ultrasonic after carbonization pretreatment can significantly enhance the adhesion of Ti-based diamond coatings by promoting nucleation and suppressing the formation of porous titanium carbide.

Structure and photoluminescence properties of MoO3−x/graphene nanoflake hybrid nanomaterials formed via surface growth

An unconventional method based on hot filament chemical vapor deposition system is used to fabricate MoO3−x/graphene nanoflake hybrid structures via surface growth. MoO3 precursor is firstly reduced to MoO3−x nanoparticles mediated by N2 molecules excited by electrons emission from hot tungsten filaments. Graphene nanoflakes are then grown on the MoO3−x nanoparticles in a high-flow-rate CH4 environment through the surface conversion of hydrocarbon radicals to benzene. The results indicate that the MoO3−x nanoparticles are mainly composed of Mo4O11 and MoO2 phases and they are covered by the graphene nanoflakes formed via surface growth. This new hybrid structure emits the ultraviolet, blue, green, red and infrared light and the photoluminescence of MoO3−x nanoparticles is quenched by the graphene nanoflakes. The generation of prevailing photoluminescence bands is interpreted by the three mechanisms including the near band edge emission, the transition between two bands and the inter-valence charge transfer transition, which indicates that the intermediate band formed within the bandgap by electrons from oxygen vacancies may cause the emission. The observed photoluminescence quenching of MoO3−x nanoparticles originates from the transfer of electrons from MoO3−x nanoparticles to graphene nanoflakes under electric field formed in the MoO3−x/graphene nanoflake interface. These results not only provide further insights into the rich surface properties of graphene/molybdenum oxide hybrid structures but also contribute to the design and synthesis of new materials and the development of next-generation graphene-based optoelectronic and photovoltaic devices.

Manipulation of nanostructured carbon films as field emitters in an electric-and-magnetic-field-assisted chemical vapor deposition process

To enhance the field emission performance and understand the emission essence of carbon materials, carbon films with different morphology and phase composition were fabricated by regulating the reactive gas flow ratio in a hot filament chemical vapor deposition system with the assistance of electric field and magnetic field. The characterization of carbon film quality and measurement of their field emission performance indicated that carbon nanostructures, including nanoclusters, nanopillars and nanotips, which were determined by the methane concentration in the process, were formed under the assistance of electric field. Further magnetic field assistance could lead to the formation of finer nanostructures with higher crystallinity. Field emission performance was highly dependent on the morphology and phase composition of the carbon films. Among all the samples, carbon nanotips, deposited in high methane concentration with the co-assistance of magnetic and electric field, possessed the best field emission performance, with the lowest turn-on field of 6.5 V·μm−1 (J = 10 μA·cm−2). Besides, a comparative study on the fitting degree of several conduction mechanisms revealed that the essence of field emission was the combination of several emission mechanisms, which was also dependent on the morphology and phase composition of these carbon films.

Integrated photocapacitors based on dye-sensitized TiO2/FTO as photoanode and MnO2 coated micro-array CNTs as supercapacitor counter electrode with TEABF4 electrolyte

Harvesting solar energy using dye-sensitized solar cells (DSSCs) has been a promising option. Successful integration of a DSSC electrode with an energy storage electrode represents the next challenge for the researchers. In this paper, the fabrication and characterization of an integrated dye-sensitized photoanode and a supercapacitor cathode or a photocapacitor has been presented. This novel device employs N-719 dye-sensitized titanium dioxide on fluorine-doped tin oxide glass substrate as the photoanode. The supercapacitive counter electrode comprises MnO2 coated, vertically aligned, micro-array patterned carbon nanotubes (MA-CNTs). The CNTs were grown on n++ silicon (Si) substrates in a hot filament chemical vapor deposition system followed by in-situ electrochemical deposition of MnO2. Tetraethyl ammonium tetrafluoroborate electrolyte was used to investigate the photovoltaic and energy storage performances of the photocapacitors under 1-sun illumination and constant-current discharge tests. A high discharge capacitance of 13 mF/cm2 at 0.932 V was achieved by coating MnO2 onto the high surface area of MA-CNTs due to the pseudocapacitive behavior of MnO2, which led to a nearly 3-fold increase in the short circuit current density to 0.749 mA/cm2 and more than a 2-fold enhancement in the open circuit voltage to 0.46 V, as compared to the baseline CNT counter electrode. The corresponding increase in the fill factor and efficiency was also observed. Overall, we have demonstrated the viability of a compact, easy to fabricate, integrated photocapacitor with promising energy generation/storage performance.

Reducing edge effect of temperature-field for large area thin film deposition in hot filament chemical vapor deposition system

Reducing edge effect of temperature-field for large area thin film deposition in hot filament chemical vapor deposition system

Raman scattering of nitrogen incorporated diamond thin films grown by hot filament chemical vapor deposition

A detailed Raman scattering analysis of nitrogen incorporated polycrystalline diamond thin films grown using NH3/CH4/H2 gas mixture in hot filament chemical vapor deposition system is presented. To understand the nitrogen bonding configuration in these films, diamond films are grown by replacing H2 with D2 in the gas mixture. The Raman peak observed at ~1190 cm−1 showed an isotopic shift to ~830 cm−1 upon replacing H2 with D2 in the gas mixture. With the present Raman analysis, the peak at ~1190 cm−1 is assigned to CNH. Secondary ion mass spectroscopy revealed the abundance of nitrogen in the sub-surface region of the annealed diamond thin films.

THE EFFECTS OF BORON DOPING ON RESIDUAL STRESS OF HFCVD DIAMOND FILM FOR MEMS APPLICATIONS

In this study, the residual stress of boron-doped diamond (BDD) films is investigated as a function of boron doping level using X-ray diffraction (XRD) analysis. Boron doping level is controlled from 1000[Formula: see text]ppm to 9000[Formula: see text]ppm by dissolving trimethyl borate into acetone. BDD films are deposited on silicon wafers using a bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) system. Residual stress calculated by [Formula: see text] method varies linearly from [Formula: see text]2.4[Formula: see text]GPa to [Formula: see text]1.1[Formula: see text]GPa with increasing boron doping level. On the BDD film of [Formula: see text]1.75[Formula: see text]GPa, free standing BDD cantilevers are fabricated by photolithography and ICP-RIE processes, then tested by laser Doppler vibrometer (LDV). A cantilever with resonant frequency of 183[Formula: see text]KHz and [Formula: see text] factor of 261 in the air is fabricated.

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.

Bottom-up diamond nanorod growth in HFCVD from nanocrystalline diamond film as a template-free method

Nanocrystalline diamond (NCD) films are being used in a large number of applications. Also, diamond nanorods (DNRs) exhibit distinctive features that are not present in diamond films, because of the tunable large surface-to-volume ratio and tubular configuration. In this work, we report on the synthesis of DNRs by means of the bottom-up and template-free method from NCD films by the hot filament chemical vapor deposition system. The substrate materials used for diamond deposition were stainless steel (AISI 316) and chromium nitride-coated stainless steel. On both substrates, NCD films and then DNRs have been synthesized. The micro-Raman confirms that the synthesized structure is NCD. In addition, the grazing incident x-ray diffraction pattern confirms the presence of cubic diamond and rhombohedral diamond as a film on the CrN and Cr2N interlayer. Also, the DNRs are encased in an amorphous carbon (a-C) shell. The DNRs are grown on the NCD grains by a bottom-up technology and template-free method. Their orientations are almost random in the diamond thin-film surface. In addition, the density of DNRs on the NCD film for the CrN interlayer is more than for the stainless-steel substrate. The NCD/DNR films are dense, adhesive, continuous, and almost uniform on the CrN-coated stainless-steel substrate.

Structural and photoluminescent properties of a composite tantalum oxide and silicon nanocrystals embedded in a silicon oxide film

Tantalum oxide crystals encrusted in a silicon oxide matrix were synthesized by using a hot filament chemical vapor deposition system (HFCVD). A solid source composed by a mixture in different percentages of Ta2O5 and silicon (Si) powders were used as reactants. The films were grown at 800°C and 1000°C under hydrogen ambient. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) at room temperature. From the XPS results it was confirmed the formation of a mixture of Tantalum oxide, silicon oxide and Si nanoparticles (Ta2O5-SiO2-Si(nc)) as seen from the Si (2p) and Ta (4f) lines corresponding to Si+ and Ta+ states respectively. Ta2O5 and Si nanocrystals (Si-NCs) embedded in the silicon oxide films were observed on HRTEM images which corroborate the XPS results. Finally the emission properties of the films exhibited a broad band from 400 to 850nm caused by the independent PL properties of tantalum oxide and Si-NCs that compose the film. The intensity of the emissions was observed to be dependent on both temperature of deposition and the ratio Ta2O5/Si, used as initial reactants. Results from this work might supply useful data for the development of future light emitter devices.

Ingenious design of Cu/Ni substrate for hot filament chemical vapor deposition growth of high quality graphene films

The Cu/Ni substrates were fabricated at low defect densities of the Ni substrates by RF magnetron sputtering and the composition of Cu atoms on Ni substrates were modulated by the sputtering time. The high-quality graphene films were fabricated on the Cu/Ni substrates by hot filament chemical vapor deposition system (HFCVD). The ID/IG ratios were very low (<<0.1) for all samples, which reflected the high-quality graphene films were obtained. The composition of Cu atoms played an important role in the growth of graphene films. Based on the dissolution precipitation mechanism of Ni and the absorption and self-limiting mechanism of Cu on the Cu/Ni substrates, it has been found that the layers of graphene was restrained by the composition of Cu atoms. Different layers of high-quality graphene films were obtained. A new growth mechanism of fabrication method was proposed by this investigation.

Improving the long-term stability of Ti6Al4V abutment screw by coating micro/nano-crystalline diamond films

Abutment screw loosening is the most common complication of implanting teeth. Aimed at improving the long-term stability of them, well-adherent and homogeneous micro-crystalline diamond (MCD) and nano-crystalline diamond (NCD) were deposited on DIO® (Dong Seo, Korea) abutment screws using a hot filament chemical vapor deposition (HFCVD) system. Compared with bare DIO® screws, diamond coated ones showed higher post reverse toque values than the bare ones (p<0.05) after cyclic loading one million times under 100N, and no obvious flaking happened after loading test. Diamond coated disks showed lower friction coefficients of 0.15 and 0.18 in artificial saliva when countered with ZrO2 than that of bare Ti6Al4V disks of 0.40. Though higher cell apoptosis rate was observed on film coated disks, but no significant difference between MCD group and NCD group. And the cytotoxicity of diamond films was acceptable for the fact that the cell viability of them was still higher than 70% after cultured for 72h. It can be inferred that coating diamond films might be a promising modification method for Ti6Al4V abutment screws.