Hot-filament Chemical Vapor Deposition Technique Research Articles

Influence of the Incorporation of Nd in ZnO Films Grown by the HFCVD Technique to Enhance Photoluminiscence Due to Defects

In this work, optical–structural and morphological behavior when Nd is incorporated into ZnO is studied. ZnO and Nd-doped ZnO (ZnO-Nd) films were deposited at 900 °C on Silicon n-type substrates (100) by using the Hot Filament Chemical Vapor Deposition (HFCVD) technique. For this, pellets were made by from powders of ZnO(s) and a mixture of ZnO(s):Nd(OH)3(s). The weight percent of the mixture ZnO:Nd(OH)3 in the pellet is 1:3. The gaseous precursor generation was carried out by chemical decomposition of the pellets using atomic hydrogen which was produced by a tungsten filament at 2000 °C. For the ZnO film, diffraction planes (100), (002), (101), (102), (110), and (103) were found by XRD. For the ZnO-Nd film, its planes are displaced, indicating the incorporation of Nd into the ZnO. EDS was used to confirm the Nd in the ZnO-Nd film with an atomic concentration (at%) of Nd = 10.79. An improvement in photoluminescence is observed for the ZnO-Nd film; this improvement is attributed to an increase in oxygen vacancies due to the presence of Nd. The important thing about this study is that by the HFCVD method, ZnO-Nd films can be obtained easily and with very short times; in addition, some oxide compounds can be obtained individually as initial precursors, which reduces the cost compared to other techniques. Something interesting is that the incorporation of Nd into ZnO by this method has not yet been studied, and depending on the method used, the PL of ZnO with Nd can increase or decrease, and by the HFCVD method the PL of the ZnO film, when Nd is incorporated, increases more than 15 times compared to the ZnO film.

Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS

Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS

Nanostructured boron-doped diamond electrodes for two-electron water oxidation to produce hydrogen peroxide

Boron-doped diamond (BDD) electrodes have been widely used in water treatment, e.g., degradation of antibiotics and pigments for water purification. Hydrogen peroxide production by two-electron electrochemical oxidation of water is a green and attractive method that has the potential to replace the conventional anthraquinone autoxidation (AO) process. In this study, BDD films were prepared on single-crystal silicon wafers by using hot-filament chemical vapor deposition (HFCVD) technique. Then, dense tubular nanostructure (nanotubes) arrays were prepared on the BDD films employing inductively coupled plasma (ICP) etching. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) proved the formation of oxygen-terminated nanostructures, which was ascribed to the oxygen plasma and the self-masking. The length of diamond nanotubes as well as the root diameter increased gradually and non-linearly with the increase of etching time. It was indicated by cyclic voltammetry (CV) analysis that the effective active area of the electrodes increased after etching, and variations of resulting reaction performance were observed. The oxygen-terminated and nanostructured BDD electrode obtained by etching with the optimized parameters features better electrocatalytic performance, with reduced oxidation potential and 46.8 % higher Faraday Efficiency (FE) for hydrogen peroxide production, compared to the original BDD sample. Therefore, the manufacturing of nanostructures is an effective method to improve the efficiency of BDD water oxidation for the production of hydrogen peroxide.

Enhancing Interfacial Capacitance by Boron Doping in Vertically Porous Carbon Toward High-Performance AC Filtering Electrochemical Capacitors.

Electrochemical capacitors (ECs) show great perspective in alternate current (AC)filtering once they simultaneously reach ultra-fast response and high capacitance density. Nevertheless, the structure-design criteria of the two key properties are often mutually incompatible in electrode construction. Herein, it is proposed that combining vertically oriented porous carbon with enhanced interfacial capacitance (Ci ) can efficiently solve this issue. Theoretically, the density function theory calculation shows that the Ci of a carbon electrode can be enhanced by boron doping due to the corresponding compact induced charge layer. Experimentally, the vertical-oriented boron-doped graphene nanowalls (BGNWs) electrodes, whose Ci is enhanced from 4.20 to 10.16µFcm-2 upon boron doping, are prepared on a large scale (480 cm2 ) using a hot-filament chemical vapor deposition technique (HFCVD). Owing to the high Ci and vertically oriented porous structure, BGNWs-based EC has a high capacitance density of 996µFcm-2 with a phase angle of - 79.4° at 120Hz in aqueous electrolyte and a high energy density of 1953µFV2 cm-2 in organic electrolyte. As a result, the EC is capable of smoothing 120Hz ripples for 60Hz AC filtering. These results provide enlightening insights on designing high-performance ECs for high-frequency applications.

Influence of diamond matrix morphology on ZnO surface morphology and preferred orientation

The signal propagation loss and conversion efficiency are two critical performances of diamond/ZnO film-based surface acoustic wave (SAW) device, and depend on roughness and preferred orientation degree (POD) of ZnO surface layer at plane (002). In-situ improvement of operational performance of ZnO layer is achieved by adjusting morphology of diamond matrix layer via diamond particle size. Diamond layer is deposited on silicon substrate using hot-filament chemical vapor deposition (HFCVD) technique by varying Ar/(Ar+H2) ratio. The ZnO layer is then deposited on the diamond film using radio-frequency magnetron sputtering (RFMS). The results show that, by regulating the diamond particle size, it is possible to adjust morphology of the diamond layer and facilitate variation in morphology and preferred orientation of ZnO layer for a better operational performance of SAW device. When the diamond particle size is decreased from 1.38 to 0.12 µm, the root-mean-square (RMS) roughness of ZnO layer initially drops and then rises, and the lowest roughness is 6.4 nm. Also, POD of ZnO (002) increases from 2.61 to 2.89, and then drops to 2.83. For a diamond particle size of 0.35 µm, the RMS roughness of ZnO layer has minimum value of 6.4 nm, and the POD of ZnO (002) approaches the maximum of 2.89 with a half-peak width of 0.36˚. The influence of diamond layer morphology on ZnO morphology and POD is thus proposed.

Direct-drive implosion experiment of diamond capsules fabricated with hot filament chemical vapor deposition technique

Diamond is a promising alternative capsule material for direct-drive inertial confinement fusion. Previous investigations suggest that the stiffness and higher density of diamond can mitigate laser imprinting, which is an initial perturbation on the ablation surface caused by non-uniform laser irradiation. We conduct diamond capsule fabrication using the hot filament chemical vapor deposition (HF-CVD) technique. This technique is the most suitable diamond deposition method in terms of mass production, since the deposition area can be easily extended just by increasing the number of hot filaments. This paper presents the first direct-drive implosion experiment concerning diamond capsules fabricated using the HF-CVD technique. The compression of thin diamond capsules, with an inner capsule diameter of 482 μm and a shell thickness of 1.6 μm, is successfully achieved, and the implosion trajectory of diamond capsules, with the same diameter and thickness, is consistent with 1D radiation hydrodynamic simulation calculations. However, for diamond capsules with an inner diameter of 482 μm and a shell thickness of 2.4 μm, asymmetry of the implosion trajectory and unexpected x-ray emission are observed. This is attributed to the remaining silicon (Si) mold inside the capsule left over from the fabrication process, revealing that the etching method of Si in diamond capsules should be improved.

Orientation Dependence of Cathodoluminescence and Photoluminescence Spectroscopy of Defects in Chemical-Vapor-Deposited Diamond Microcrystal.

Point defects, impurities, and defect–impurity complexes in diamond microcrystals were studied with the cathodoluminescence (CL) spectroscopy in the scanning electron microscope, photoluminescence (PL), and Raman spectroscopy (RS). Such defects can influence the directions that microcrystals are grown. Micro-diamonds were obtained by a hot-filament chemical vapor deposition (HF CVD) technique from the methane–hydrogen gas mixture. The CL spectra of diamond microcrystals taken from (100) and (111) crystallographic planes were compared to the CL spectrum of a (100) oriented Element Six diamond monocrystal. The following color centers were identified: 2.52, 2.156, 2.055 eV attributed to a nitrogen–vacancy complex and a violet-emitting center (A-band) observed at 2.82 eV associated with dislocation line defects, whose atomic structure is still under discussion. The Raman studies showed that the planes (111) are more defective in comparison to (100) planes. What is reflected in the CL spectra as (111) shows a strong band in the UV region (2.815 eV) which is not observed in the case of the (100) plane.

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.

Characterization of Micro-Crystalline Diamond Tools Synthesized by HFCVD Process with Different Seeding Powders

Synthesis of diamond films on carbide insert is a recent area of research in surface engineering. This research is carryout to know the effect of different seeding powders on diamond coating of WC tool by Hot Filament Chemical Vapor Deposition (HFCVD) method. Here, the formation of microcrystalline diamond (MCD) on SPUN tungsten carbide (WC-Co) cutting tool insert is carried out. Basically, before coating in HFCVD method, the substrate cobalt content should minimize by ultra-sonic etching. The uncoated tools are seeded ultrasonically by Diamond, Iridium, Platinum and Tungsten powder at the same coating condition to observe the growth of diamond crystals. X- ray diffraction gives clear results of diamond plane and adhesion of coating. The purity of diamond crystal after coating can be clear by observing the Raman shift in Raman spectroscopy (RS). The tool is seeded with diamond powder gives more nucleation density due to the presence of more sp3 bond as compared with sp2. Use of diamond and platinum powder as a seeding material gives fully developed crystal and uniform coating during diamond film deposition by HFCVD technique, rather in case of other powder coating the discrete crystals were formed.

Study of cutting force and tool wear during turning of aluminium with WC, PCD and HFCVD coated MCD tools

Enormous developmental work has been made in synthesis of metastable diamond by hot filament chemical vapor deposition (HFCVD) method. In this paper, micro-crystalline diamond (MCD) was deposited on WC–6 wt.% Co cutting tool inserts by HFCVD technique. The MCD coated tool was characterized by the scanning electron microscope (SEM), X-ray diffraction (XRD) and micro Raman spectroscopy (μ-RS). A comparison was made among the MCD tool, uncoated tungsten carbide (WC) tool and polycrystalline diamond (PCD) tool during the dry turning of rolled aluminum. The various major tests were conducted such as surface roughness, cutting force and tool wear, which were taken into consideration to establish a proper comparison among the advanced cutting tools. Surface roughness was measured during machining by Talysurf. The tool wear was studied by SEM after machining. The cutting forces were measured by Kistler 3D-dynamometer during the machining process. The test results indicate that, the CVD coated MCD tool and PCD tool produced almost similar results. But, the price of PCD tools are five times costlier than MCD tools. So, MCD tool would be a better alternative for machining of aluminium.

Diamond Thin Film Coating on WC Substrate by HFCVD Method using Different Seeding Powders and Its Characterization

The formation of diamond thin solid film is studied by Hot Filament Chemical Vapor Deposition (HFCVD) by using different seeding powders on WC substrate. Here, we have deposited microcrystalline diamond (MCD) on SPUN cemented carbide (WC-Co) cutting tool insert using conventional HFCVD technique. The substrates were ultrasonically seeded with titanium, tungsten, molybdenum, diamond, combined diamond and tungsten powder at the same operation parameters to observe the difference in the growth of diamond by different seeding. Nucleation of diamond coating was studied after 40 minutes of coating with seeded substrate. The physical characteristics were studied by X-ray Diffraction (XRD).The Scanning Electron Microscope (SEM) was used to study the surface morphology. The diamond purity was studied with the help of Raman spectroscopy (RS). Reduction of cobalt percentage before and after pretreatment was studied by Energy Dispersive Spectroscopy (EDS). A very dense and uniform coating was deposited on the diamond powder seeded substrate. The nucleation density was found to be highest in diamond powder when compared with molybdenum and tungsten powder individually, because in initial stage the deposited material contains more sp2 content as compared to sp3 content. By using diamond and tungsten mixed powder the coating was uniform rather in case of only tungsten powder coating the discrete crystals were formed.

Low temperature HFCVD synthesis of tungsten oxide thin film for high response hydrogen gas sensor application

• WO 3 thin films are obtained through low temperature HFCVD technique. • WO 3 thin films exhibits cauliflower morphology (WCNs) with typical monoclinic WO 3 crystal structure. • Highly uniform WCNs thin film is prepared. • High sensitivity of ∼87% towards H 2 gas is achieved. A quick and efficient approach was employed for the growth of nanocrystalline tungsten oxide (WO 3 ) thin films using one-step hot filament chemical vapor deposition (HFCVD) method at low temperature. In a typical experiment, the parent material tungsten (W) was subjected to oxidation, gasification and its subsequent condensation to obtain the uniform deposition of WO 3 thin film on silicon substrate at significantly low temperature of ∼200 °C. Prepared WO 3 thin film possessed the cauliflower nanostructure (WCNs) with typical monoclinic WO 3 crystal structure. Prepared WCNs thin films were applied for the detection of hydrogen (H 2 ) gas at 100 ppm. H 2 response increased with rise in temperature and the maximum response of ∼87% was obtained at the optimized temperature of ∼250 °C with response time 180 s.

Analysis of Parameters Affecting the Surface Roughness in Sapphire Wafer Polishing Using Nanocrystalline–Microcrystalline Multilayer Diamond CVD Pellets

To reduce the processing cost and to polish high hardness substrates, a change from the currently used slurry process to the process using fixed abrasive grain is required. Therefore, studying the fixed abrasive tool to improve yield and process stability is important. In this study, a chemical vapor deposition (CVD) diamond pellet with an artificially controlled contact area was applied to replace the slurry polishing process. The CVD diamond pellets were prepared by depositing a microcrystalline diamond on silicon nitride ceramic substrates using a hot filament CVD technique and preparing a multi-layered pellet in which a nanocrystalline diamond (NCD) was deposited. The influences of the real contact area of CVD diamond on the surface roughness and material removal rate were studied using scanning electron microscopy, a stylus profilometer, atomic force microscopy, and Raman spectroscopy before and after polishing. In addition, the polishing effect of the sapphire wafer was analyzed and predicted by modeling the roughness and the real contact area of the diamond CVD pellet. To analyze the polishing characteristics according to changes in the area, the surface roughness of the NCD was varied from 65 to 115 nm, and the polishing was evaluated. The results showed that compared with the process using diamond slurry, the multilayer diamond pellet had a higher material removal rate and the same surface roughness and total thickness variation.

The effect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating in hot filament chemical vapor deposition

AbstractEffect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating produced by hot filament chemical vapor deposition (HFCVD) process was studied. Annealed sheets of 316L stainless steels were used as the substrate. HFCVD technique, with substrate temperatures of 400 and 500°C, was used to deposit tungsten carbide coating on these sheets. Field Emission Scanning Electron Microscope (FE‐SEM) was used to study the evolution of microstructure. X‐Ray Diffraction spectroscopy was used to analyze the phases formed and Raman spectroscopy was employed to differentiate molecular composition of the coatings. The amount of the porosity of the coatings was measured and Vickers hardness measurement was used for hardness assessment. Results show that the tungsten carbide coatings have a honeycomb structure and increasing the temperature of the substrate increases the amount of porosity of the coating. XRD results showed that 3 different crystalline structures containing W, WC, and W2C were formed in the coating deposited on the 316L stainless steel. Increasing the temperature of the deposition has increased the intensity of the peaks in the XRD results. Raman spectroscopy results indicated the presence of a carbon in the tungsten carbide coatings. Finally, microhardness of the tungsten carbide coating increases with increasing the temperature of the substrate.

Tungsten oxide thin films: detection and trapping of hazardous gases

Synthesis of tungsten (W) and tungsten tri-oxide (WO3) thin films on alumina substrate by a peculiar Red-ox reaction route using hot-filament chemical vapor deposition technique is described. The resulting tungsten and tungsten oxide films were characterized using various techniques such as x-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM). XRD results revealed the complete conversion of cubic phase of pure tungsten into monoclinic phase of tungsten oxide. Raman spectroscopic analysis also confirmed the formation of WO3. SEM images show considerable alteration in morphology from well faceted particles to wafers when pure W-film was converted to WO3 film. The wafer like morphology of WO3 films is found to be suitable for gas sensing towards hazardous gases such as NO2 and NH3. The WO3 films showcased their highly responsive nature towards NO2 gas with exceptionally high gas sensitivity ~32. WO3 film demonstrated longer recovery time towards NO2 gas unlike NH3 gas making them attractive for their utilization in ‘Newer application’ such as a catalyst support material in catalytic converter devices which are potential representatives to arrest pollutant gases (NO2) getting flown into the living environment.

On the development of a dual-layered diamond-coated tool for the effective machining of titanium Ti-6Al-4V alloy

This work is focused on the development of a dual-layered diamond-coated tungsten carbide tool for machining titanium Ti-6Al-4V alloy. A hot-filament chemical vapor deposition technique was used to synthesize diamond films on tungsten carbide tools. A boron-doped diamond interlayer was added to a microcrystalline diamond layer in an attempt to improve the interface adhesion strength. The dual-layered diamond-coated tool was employed in machining at cutting speeds in the range of 70 to 150 m min−1 with a lower feed and a lower depth of cut of 0.5 mm rev−1 and 0.5 mm, respectively, to operate in the transition from adhesion- to diffusion-tool-wear and thereby arrive at suitable conditions for enhancing tool life. The proposed tool was then compared, on the basis of performance under real-time cutting conditions, with commercially available microcrystalline diamond, nanocrystalline diamond, titanium nitride and uncoated tungsten carbide tools. The life and surface finish of the proposed dual-layered tool and uncoated tungsten carbide were also investigated in interrupted cutting such as milling. The results of this study show a significant improvement in tool life and finish of Ti-6Al-4V parts machined with the dual-layered diamond-coated tool when compared with its uncoated counterpart. These results pave the way for the use of a low-cost tool, with respect to, polycrystalline diamond for enhancing both tool life and machining productivity in critical sectors fabricating parts out of titanium Ti-6Al-4V alloy. The application of this coating technology can also be extended to the machining of non-ferrous alloys owing to its better adhesion strength.

Surface modifications on as-grown boron doped CVD diamond films induced by the B2O3–ethanol–Ar system

The surface termination of as-grown microcrystalline (MCD) and nanocrystalline (NCD) boron-doped diamond films was assessed by X-ray photoelectron spectroscopy (XPS) and water contact angle techniques. The diamond coatings were grown on mirror-polished silicon nitride ceramic substrates using the hot-filament chemical vapor deposition (HFCVD) technique. The boron doping source, boron oxide (B2O3) diluted in ethanol, was dragged by a constant Ar flow at different CH4/H2 gas ratios and system pressures. The electrical resistivity of these semiconducting diamond films was obtained and their surfaces were further characterized by scanning electron microscopy (SEM) and Raman spectroscopy.The results have shown that the increasing total pressure particularly affects the crystal size of the boron doped MCD samples by enhancing diamond renucleation due to the higher residence time of Ar. Also, both as-grown MCD and NCD surface types were found to be inherently hydrophobic, with contact angles ~90°C, but retain significant amounts of oxygen bonded to carbon atoms mainly as C–O–C and C=O terminations. Such partial diamond surface oxidation is the result of a very unique stable gas mixture containing hydrogen, carbon and oxygen, when boron oxide and ethanol are added to methane during the CVD process.

Fabrication of high-quality graphene by hot-filament thermal chemical vapor deposition

To the best of our knowledge, the previously reported graphene fabricated using catalytic chemical vapor deposition techniques contained a high defect density, which will hinder its opto-electronic properties. In this work, the effects of two crucial parameters, namely deposition time and hydrogen flow rate on the growth of graphene using a hot-filament thermal chemical vapor deposition technique were systematically studied. Fabrications were conducted at substrate and filament temperatures of 1000°C and 1750°C, respectively. Very low ID/IG ratios (≪0.1) were obtained for all the samples, which reflected the formation of high-quality graphene deposited on Cu foils. A quasi-static equilibrium copper vapor inside an alumina tube was found to be an important factor to obtain a low defect density graphene. A growth mechanism was then proposed, where the cuprous oxide (Cu2O) acted as a nucleation site for graphene growth.

RETRACTED: Growth of boron-doped diamond nanoclusters using the HFCVD technique

Boron-doped diamond nanocrystals were grown on Si wafers through introduction of the gas mixture of B2O3 dissolved in ethanol and hydrogen by a hot filament chemical vapor deposition (HFCVD) technique. Boron level in diamond films were controlled in the range from 100 to 500 ppm by adjusting the B/C ratios of gas mixtures in order to synthesize and improve the conductivity and quality of HFCVD diamond films with cluster size of nanometer. To investigate the effect of different boron percentage in the chamber on deposited films, Raman spectroscopy, field emission scanning electron microscopy and four point probe techniques were applied to characterize the properties of diamond films. Experimental results indicated that higher boron incorporation in the diamond films introduced bigger crystal clusters, better crystal quality and smaller film resistivity when the level of boron increased from 100 to 300 ppm, while they showed an opposite trend with a further increase of boron level from 300 to 500 ppm. However, in any case the higher boron-doping level led to a decrease of the non-diamond phase in the nanodiamond films.

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

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