Hot Filament Research Articles

Geological Evidence does not Support a Shallow Origin for Diamonds in Ophiolite

Geological Evidence does not Support a Shallow Origin for Diamonds in Ophiolite

Novel structuring technique for diamond coatings

Here we report a novel structuring technique for diamond coatings using a copper masking on a previously deposited diamond layer to epitaxially grow a subsequent diamond layer only at the exposed areas of the mask. An 8 μm thick copper mask is applied onto the substrate using physical vapor deposition and structured by standard photolithographic methods. Hot filament chemical vapor deposition is used to grow the 14 μm thick structured diamond layer on the diamond coated silicon wafer. Micro and nano crystallinity of the diamond layers are varied, as well as the doping with boron to verify the applicability of the new structuring method for different kinds of diamond qualities. It is shown that four-inch wafers can be fully structured with this high temperature masking technique and the resolution was mostly affected by the quality of the printed mask used for the photolithographic structuring of the copper mask. This diamond structuring method could pave the way for diamond being used in electronics or adding additional functionalities to diamond coated tools.

MeerKAT’s discovery of a radio relic in the bimodal merging cluster A2384

ABSTRACT We present the discovery of a single radio relic located at the edge of the galaxy cluster A2384, using the MeerKAT radio telescope. A2384 is a nearby (z = 0.092), low-mass, complex bimodal, merging galaxy cluster that displays a dense X-ray filament (∼700 kpc in length) between A2384(N; northern cluster) and A2384(S; southern cluster). The origin of the radio relic is puzzling. Using the MeerKAT observation of A2384, we estimate that the physical size of the radio relic is 824 × 264 kpc2 and that it is a steep spectrum source. The radio power of the relic is $P_{1.4\mathrm{GHz}}\, \sim$ (3.87 ± 0.40) × 1023 W Hz−1. This radio relic could be the result of shock wave propagation during the passage of the low-mass A2384(S) cluster through the massive A2384(N) cluster, creating a trail appearing as a hot X-ray filament. In the previous GMRT 325 MHz observation, we detected a peculiar FR I radio galaxy interacting with the hot X-ray filament of A2384, but the extended radio relic was not detected; it was confused with the southern lobe of the FR I galaxy. This newly detected radio relic is elongated and perpendicular to the merger axis, as seen in other relic clusters. In addition to the relic, we notice a candidate radio ridge in the hot X-ray filament. The physical size of the radio ridge source is ∼182 × 129 kpc2. Detection of the diffuse radio sources in the X-ray filament is a rare phenomenon, and could be a new class of radio source found between the two merging clusters of A2384(N) and A2384(S).

Nanostructured boron-doped diamond electrode for degradation of the simulation wastewater of phenol

The applications of a boron-doped diamond (BDD) used in electrode application for toxic and refractory organic degradation have attracted much attention, and its efficiency is considered to be an important factor for its practical application. In this study, BDD thin films were prepared on Ti plates by double bias-assisted hot filament chemical vapor deposition (HFCVD) technique. A reactive ion etching process was introduced by a positive grid bias and a negative substrate bias which can generate an electric field in HFCVD system. Then a novel structure of BDD electrode with nanocone arrays was successfully etched from a flat diamond thin film by this system. The addition of the bias greatly improved the etching efficiency and promoted the formation of nanocones structures. The cyclic voltammograms (CV) test showed nanostructured BDD (NBDD) electrodes had excellent electrochemical performance almost the same as that of the electrodes with untreated surfaces. It had a large effective electroactive surface area (EASA), which was 31.0% greater than the unetched electrode. As a result, the NBDD electrode exhibited improved electrocatalytic performance as compared with the untreated one, i.e., an about 24.3% increase of chemical oxygen demand (COD) removal efficiency. Among them, the superiority of NBDD electrode was obvious in the initial stage due to its highest concentration in the initial stage. In addition, the NBDD electrode achieved higher average current efficiency (ACE) as compared with the untreated one.

Study on the effect of Ar-containing work gas on the microstructure and tribological behavior of nanocrystalline diamond coatings

Using a combined pretreatment of sand-blasting and two-step etching, nanocrystalline diamond coatings with primarily diamond crystallites and good adhesion were deposited onto carbide cement by tuning the Ar/H2 ratio in the hot filament chemical vapor deposition (HFCVD) work gas. The microstructure, bonding structure, surface morphology and roughness, and wear scar were characterized using a scanning electron microscope, an atomic force microscope, a white light interferometer, and a Raman spectrometer. The dry sliding behavior of the coating against Si3N4 was tested using a pin-on-disc instrument. It was found that the addition of Ar to the HFCVD work gas can enhance grain refinement and tune the morphology of the nanocrystalline coatings. The roughness was reduced from 87.7 nm for the coating prepared without Ar to 6.21 nm for the coating prepared with 90% Ar. With the addition of Ar, the friction coefficient and wear rate decrease monotonically. The wear rate of the coating prepared with 90% Ar was less than 5% that of the coating prepared without Ar, and the wear mechanism transforms from spallation to be limited by the stress-induced sp2 tribo-layer.

Improving Pressure–Velocity Limit of Mechanical Seal with Polycrystalline Diamond Coating

Polycrystalline diamond (PCD)-coated mechanical seal rings were prepared by hot filament chemical vapor deposition (HFCVD) on graphite-loaded silicon carbide (GSiC) substrates. From the initial deposition process, the diamond first nucleated and then grew into a dense coating with grain size of 4 μm and thickness of 12.3 μm. The well-grown PCD coating, as confirmed by Raman spectroscopy and X-ray diffractometry, significantly improves the pressure–velocity limit of the mechanical seal applied in harsh operating conditions, no matter whether for a hard-to-soft mating combination or a hard-to-hard mating combination. Comparing GSiC against sintered silicon carbide (SSiC) combination (GSiC/SSiC), GSiC against graphite combination (GSiC/graphite) and PCD against graphite combination (PCD/graphite), PCD against SSiC combination (PCD/SSiC) shows the highest pressure velocity (PV) limit of 42.31 MPa·m/s with 4 kN loading at 4500 rpm rotation speed. An extremely low and stable friction coefficient and super mechanical properties under harsh conditions can be approved as the source of the high PV limit of PCD coating. A mechanical seal with PCD coating can be used for more demanding applications.

Effects of Carbonization of Filaments on CVD Diamond Thick Films Prepared by HFCVD Method

Hot filament CVD method has many advantages such as simple equipment, easy operation and low expenses, which make it the most widely used method in industrial producing diamond thick film. In this paper, tantalum filament is used in the hot filament chemical vapor deposition apparatus to carbonize under different temperature for different time, then nucleation experiments are carried out on molybdenum substrate. SEM and EDS are used to observe the surface morphology and analyze the components of the carbonized filament and substrate. The results show that lasting the carbonization time can improve the nucleation density in preparing diamond thick film,the adhesion of the diamond film also increases. Electrical resistance of the filament after carbonization can be used as a criterion to determine whether it is fully carbonized or not.

Tough negative temperature coefficient diamond thermistors comprising tungsten carbide ohmic contacts

This work presents a novel methodology for the fabrication of planar diamond film NTC (Negative Temperature Coefficient) thermistors on sintered silicon nitride (Si3N4) ceramic substrates. Such devices comprise a temperature sensitive diamond coating on one of the substrate surfaces and tungsten carbide ohmic contacts on the opposite side. Hot filament chemical vapor deposition (HFCVD) technique was used for the fabrication of both temperature sensitive flat diamond surface and WC ohmic contacts. The doping source for the semiconducting diamond layers was boron oxide dispersed in ethanol, and was added to the hydrogen/methane gas mixture using argon gas. The fabrication of WC contacts was done by first evaporating the oxide layer of the tungsten filaments used for activating the gaseous species. Hydrogenation and carburization steps were then used to produce the carbide layer. Using this approach, NTC diamond thermistors were obtained and their electrical resistance dependence with temperature was plotted and fitted to the Steinhart-Hart equation, giving β values between 1200 and 2000 K, from room temperature up to 420 °C. The WC-diamond contacts ohmic character was confirmed within the same temperature range, which highlights the potential application of such devices in precise in situ temperature measurements, at high temperature and under mechanically tough environment conditions.

Microstructure of boron doped diamond electrodes and studies on its basic electrochemical characteristics and applicability of dye degradation

The microstructure of boron doped diamond (BDD) is the main factor affecting its degradation performance, and the type of wastewater is also a major factor. In this paper, niobium based BDD electrodes were prepared by hot filament chemical vapor deposition (HFCVD) technology at 650 °C, 750 °C, 850 °C substrate temperatures. For the three BDD electrodes with different substrate temperatures, the comparison of electrochemical performance and degradation efficiency was conducted. The results showed that with the increase of deposition temperature, the microstructure of BDD electrodes surface changed, the grain size and boron content increased, and the sp3/sp2 phase ratio also increased, which caused the electrochemical oxidation performance of the BDD electrodes improved, the color removal rate of the electrodes increased, and the energy consumption reduced. The decolorization rates of the 850 °C-BDD electrode for Reactive orange X-GN and Reactive blue 19 at 180 min were 99.79 % and 93.38 %, respectively. In addition, the degradation performance of 8 dyes by 850 °C-BDD electrode was systematically studied. Affected by the molecular structure of dye, the degradation degree of each type of dye from easy to difficult was: Fuchsin acid, Reactive red 2, Acid orange G, Alizarin red, Acid blue 92, Reactive orange X-GN, Orange II, Reactive blue 19.

The effect of transition-metal seeding powder on deposition and growth of diamond synthesized by hot filament chemical vapor deposition processes on cemented carbide substrates and its characterization

Hot Filament Chemical Vapor Deposition is a well-established method to synthesize diamond thin films on a non-diamond substrate. Here, we have deposited microcrystalline diamond on tungsten carbide cutting tool insert by using conventional Hot Filament Chemical Vapor Deposition technique. The substrates were ultrasonically seeded with Carbon, Diamond, Iridium, Molybdenum, Palladium, Platinum, Tantalum, Tungsten and Chromium natural powders and thereafter were deposited with the same deposition parameters to observe the effects of different seeding powders on the diamond coating. The coated tools were characterized by X-ray Diffraction and the quality of diamond crystals was assessed by using micro Raman spectroscopy. The surface morphology was studied by utilizing Scanning Electron Microscope. The discrete spherical diamond crystals were formed with carbon powder seeding while very dense along with uniform coatings were deposited on the diamond powder seeded substrate. Larger diamond crystals with good density were observed on the palladium seeded substrate. The micro Raman spectroscopy showed mixed results of sp3 and sp2 bonding. But the palladium seeding showed clear sp3 bonding due to the formation of crystals with bigger size. The Vickers microhardness value for the substrate with diamond seeding was found to be much higher than other coated tools.

Integration of GaN and Diamond Using Epitaxial Lateral Overgrowth.

Growth of single-crystalline GaN on polycrystalline diamond is reported for the first time. The structure was achieved using a combined process including selective diamond growth on GaN/Si wafers using hot filament chemical vapor deposition (CVD) and epitaxial lateral overgrowth of GaN on the window region between then above the diamond stripes via metal organic CVD. Optimization of the growth was performed by varying the ammonia to trimethylgallium mole ratio (V/III), chamber pressure, and temperature in the range of 8000-1330, 40-200 Torr, and 975-1030 °C, respectively. A lower pressure, higher V/III ratio, higher temperature, and GaN window mask openings along [11̅00] resulted in enhanced lateral growth of GaN. Complete lateral coverage and coalescence of GaN were achieved over a [11̅00]-oriented 5 μm-wide GaN window between 5 μm diamond stripes when using V/III = 7880, P = 100 Torr, and T = 1030 °C. The crystalline quality of overgrown GaN was confirmed using cross-sectional scanning electron microscopy, high-resolution X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, and selective-area electron diffraction.

Terrella for advanced undergraduate laboratory

A terrella developed for the undergraduate Advanced Laboratory course in the University of Wisconsin-Madison Physics Department is described. Our terrella consists of a permanent magnet, mounted on a pedestal in a vacuum chamber, surrounded by electrodes that may be biased in various ways. The system can confine a plasma, which may, in some ways, be considered as a toy model of the plasma confined in the Earth's magnetosphere. Our axisymmetric plasma forms in a region where the magnitude of the magnetic field B is 14 G ≤B≤ 550 G; for typical operation, the neutral gas pressure is p∼10−4 Torr. The plasma is created by thermionic emission from a hot filament. Available diagnostics are a swept Langmuir probe, a spectroscopic fiber and visible-wavelength spectrometer, and visible imaging. In two four-hour laboratory sessions, students are guided through vacuum pumpdown, connection of electrical circuits, establishment of plasma, acquisition of data, analysis of data, and critique of data. In this paper, we present student measurements of radial profiles of electron temperature Te and density ne as well as imaging of mirror trapping and ∇B drift and curvature drift. We conclude by outlining some opportunities for additional terrella-based student experiments.

Effects of tungsten doping on structure and photoluminescence of MoO3–x nanomaterials

The challenge in molybdenum oxides intended for integration into electronic, optical, energy conversion, and other devices is tuning of their photoluminescence (PL) properties. Despite some initial studies on possibilities of tuning PL properties, this issue remains unresolved. For this reason, we explored the tailoring of PL properties of molybdenum oxide nanomaterials with a dopant through a robust synthesis by hot filament chemical vapour deposition. Here the MoO3–x nanomaterials are doped with tungsten in a low concentration, and the room temperature PL properties are studied. The obtained results highlight the interaction of Mo5+ defects and oxygen vacancies, which are playing an essential role in the enhancement of green PL emission. Moreover, the used doping method is fast and straightforward and can be used to control the structure as well as the PL properties of molybdenum oxide nanomaterials.

Spectroscopic Properties of Si-nc in SiOx Films Using HFCVD.

In the present work, non-stoichiometric silicon oxide films (SiOx) deposited using a hot filament chemical vapor deposition technique at short time and simple parameters of depositions are reported. This is motivated by the numerous potential applications of SiOx films in areas such as optoelectronics. SiOx films were characterized with different spectroscopic techniques. The deposited films have interesting characteristics such as the presence of silicon nanoclusters without applying thermal annealing, in addition to a strong photoluminescence after applying thermal annealing in the vicinity of 1.5 eV, which may be attributed to the presence of small, oxidized silicon grains (less than 2 nm) or silicon nanocrystals (Si-nc). An interesting correlation was found between oxygen content, the presence of hydrogen, and the formation of defects in the material, with parameters such as the band gap and the Urbach energies. This correlation is interesting in the development of band gap engineering for this material for applications in photonic devices.

Películas de SRO-HFCVD como dieléctrico en estructuras MIS y sus propiedades eléctricas

This paper presents the results obtained by the electrooptical characterization of a MIS structure built by depositing a film of an Indium Tin Oxide (ITO) on a Silicon Rich Oxide (SRO) film using the Chemical Vapor Deposition Hot Filament (HFCVD) system. The SROHFCVD films were deposited considering two hydrogen fluxes levels at 25 and 100 sccm, under these conditions we grow single and double films, both being heat treated at 1100 ° C to improve their optical and structural characteristics. Through of the techniques of Null Spectroscopy, XPS and Photoluminescence, it was possible to determine the thickness of the SRO films, quantify the silicon excess present in them and analyze their spectra. These films are used as the active layer in Metal-Insulating-Semiconductor (MIS) structures, such structures were electrically characterized through the I-V curves. From the result of these characterizations a comparison is made between the MIS structures with films virgin (V) and with ones heat-treated (T-T). Characterizations indicate that SRO-HFCVD films with T-T significantly modify the optical and electrical properties of MIS structures, which is promising for the design of integrated optical sensors.

Dependences of morphology and surface roughness on growth conditions of diamond capsules for the direct-drive inertial confinement fusion

In order to achieve the ignition by direct-drive inertial confinement fusion (ICF), smooth and symmetric fuel capsule is required. Our previous research found that stiffness of the capsule material contributes to reduce the laser imprinting. Therefore, diamond is considered to be the most promising candidate as the stiff ablator material for direct-drive ICF capsule. In this study, aiming at improving the surface roughness on the diamond capsule, we obtained dependence of methane concentration and gas pressure on surface roughness and morphology by hot filament chemical vapor deposition technique.

Rapid analysis of lithium in serum samples by thermal ionization ion mobility spectrometry

A new application of thermal ionization ion mobility spectrometry (TI–IMS) was presented for the fast determination of lithium ion (Li+) in serum samples. This research aims to provide a selective approach to facilitate lithium monitoring for bipolar patients. The method is based on an initial step of quick–burning the organic content of the diluted serum sample on a hot filament followed by the emission of alkali ions remained in the ash. The drift tube temperature was optimized to maximize the separation of signal from the other existing alkali ions, sodium (Na+) and potassium (K+). The filament temperature and the dilution ratio were also optimized for best observation of the Li+ signal among the excess amount of Na+ and K+. The best peak resolution was obtained at 1:200 dilution ratio and drift tube temperature of 160 °C. TI–IMS demonstrated high sensitivity in both diluted standard and serum sample solution (0.21 μM for LOD and 1.50 μM for LOQ). The Relative standard deviation of the lithium determination was obtained to be 5.4%. Method validation was conducted by comparing the results with those obtained through the inductively coupled plasma optical emission spectrometry (ICP–OES) method. A good agreement between the results was observed indicating that the TI–IMS method can be potentially applied to routine analysis of biological samples. Rapidity, ease of operation and low–cost analysis are superior features of the proposed technique over the traditional approaches.

Highly thermally conductive polymer composites with barnacle-like nano-crystalline Diamond@Silicon carbide hybrid architecture

Polymeric composites with the advantages of easy process, light weight and good chemical resistance were employed in thermal management. The construction of a new type thermal conductive filler has become an efficient method for improving the thermal transportation performance of polymer composite. In this work, a barnacle-like nano-crystalline diamond@silicon carbide (ND@SiC) is prepared through depositing ND on SiC powders in a hot filament chemical vapor deposition (HFCVD). ND@SiC/PVDF composite was prepared and their thermal transportation properties were investigated. The obtained composites with 70 wt% ND@SiC loading exhibit a high thermal conductivity of 2.39 W m−1 K−1, which increased by 1132% in comparison with the pure polymer. It is also much higher than that of the composite adding 70 wt% SiC powders (1.48 W m−1 K−1). The high thermal conductivity of polymer composites by adding the ND@SiC filler is mainly attributed to the novel barnacle-like structure. This work provides a new idea to significantly enhance thermal transportation properties of composites as used in advanced packaging materials.

Interface design to tune stress distribution for high performance diamond/silicon carbide coated cemented carbide tools

The stress distribution of the interface plays a key role in adhesion and performances of diamond coated tools. Herein, we report a combined simulation and experimental strategy to significantly minimize the thermal stress by interface design in the diamond/SiC architectures. Different diamond/SiC films, including pure diamond, composite, single SiC interlayer, gradient interlayer and multilayer, were simulated by finite element analysis and synthesized on cemented carbide tools by hot filament chemical vapor deposition (HFCVD). The stress distribution was tailored over the diamond/SiC architecture, and the maximum stress value at the cutting edge was best suppressed for the composite (58% reduction) and the gradient film (49% reduction), which resulted in the best film adhesion and were sufficient for cutting performances. The pure diamond surface ending on the gradient coated tool allowed for non-sticking machining Al-13 wt% Si alloy, resulting in enhanced workpiece quality and extended tool lifetime. Its tool lifetime was at least 7 times longer than that of the pure diamond film, and at least 4 times longer than a commercial diamond coated end mill. The diamond/SiC architectures represent a potent solution for adherent diamond coated tools with excellent machining performances.

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.