Tungsten Filament Research Articles

Effect of substrate material on the growth and field emission characteristics of large-area carbon nanotube forests

Carbon nanotubes (CNTs) are a promising replacement for tungsten filaments as electron emitters in conventional x-ray sources, owing to their higher aspect ratio, superior mechanical stability, chemical inertness, and high electrical and thermal conductivities. Conditions for realizing the best emission behavior from CNTs have been formulated over the last few years. In this paper, we report the relatively less-investigated factor, namely, the influence of the nature of substrate material on the growth as well as field emission characteristics of large-area multiwalled CNTs for their practical application in medical x-ray sources. We compare the morphology of CNTs on a variety of substrates such as stainless steel, copper, molybdenum, graphite, few-layer graphene, and carbon nanowalls grown by thermal chemical vapor deposition following a simple drop-coating of catalyst. We find that CNTs grown on stainless steel and graphite show the best combination of emission characteristics under pulsed operation mode. These studies are helpful in selecting the optimum substrate material for field emission applications. Ex situ studies on field emission degradation of CNTs are presented towards the end.

Tailoring high-temperature radiation and the resurrection of the incandescent source.

In solar cells, the mismatch between the Sun's emission spectrum and the cells' absorption profile limits the efficiency of such devices, while in incandescent light bulbs, most of the energy is lost as heat. One way to avoid the waste of a large fraction of the radiation emitted from hot objects is to tailor the thermal emission spectrum according to the desired application. This strategy has been successfully applied to photonic-crystal emitters at moderate temperatures, but is exceedingly difficult for hot emitters (>1,000 K). Here, we show that a plain incandescent tungsten filament (3,000 K) surrounded by a cold-side nanophotonic interference system optimized to reflect infrared light and transmit visible light for a wide range of angles could become a light source that reaches luminous efficiencies (∼40%) surpassing existing lighting technologies, and nearing a limit for lighting applications. We experimentally demonstrate a proof-of-principle incandescent emitter with efficiency approaching that of commercial fluorescent or light-emitting diode bulbs, but with exceptional reproduction of colours and scalable power. The ability to tailor the emission spectrum of high-temperature sources may find applications in thermophotovoltaic energy conversion and lighting.

逆向热蒸发制备望远镜主镜银反射膜

By using a high-vacuum resistive heating evaporation coating machine with the materials evaporated downwards, the research of downward thermal evaporation for large-aperture optics was implemented. The silver coating was prepared at a high deposition rate by resistive heating tungsten filaments without splashing. The adhesion layer and protective layer were also thermally evaporated downwards with specially designed evaporation boats with Cr or CrNxas the adhesion layer and SiOxor SiOxNyas the protective layer. To evaluate the performance of the protected-silver coating, three kinds of protected-silver coatings were prepared and researched in details. The reflectance, cross-section morphology and environmental stability of the prepared coating samples were characterized. The results show that the coating with 3nmCr/120nmAg/0.6nmCrNx/150nmSiOxNystructure has good performances on environmental stability and spectral characteristics. Especially, it has an average reflectance of 97.8% in the 400~1800 nm spectral range, and passed the tests of 24-hour humidity (50/98% RH) and salt folg. © 2016, Science Press. All right reserved.

外径70 mm のコンフラットフランジにマウントした簡易金属蒸着源の製作

We have constructed a simple metal evaporator mounted on a conflat flange with an outer diameter of 70 mm. It consists of a tungsten filament, an alumina tube, two molybdenum electrodes, tantalum foils, and electric feedthroughs. Evaporation rates are measured as a function of electric current. We used it to prepare an Au thin film and a Si (111)-√3 ×√3 R30°-Au surface.

High-speed infrared imaging by an uncooled optomechanical focal plane array.

In this paper, we theoretically and experimentally demonstrate that the imaging speed of the optomechanical focal plane array infrared imaging system can be significantly improved by changing the pressure in the vacuum chamber. The decrease in the thermal time constant is attributed to the additional thermal conductance caused by air. The response time will be greatly shortened to about 1/3 time in low vacuum (around ∼10(2) Pa) compared with that in high vacuum. At a chamber pressure of 50 Pa, the "trailing" in the IR image of a moving hot iron is eliminated with negligible deterioration in the image quality. Moreover, infrared images on rapid occurrence events, such as ignition of an alcohol blast burner, lighting and fusion of a tungsten filament, are captured at a frame rate up to 200 Hz. The above results show that the proposed pressure-dependent performance provides a way to improve the system imaging speed and helps to slow down a dynamic event, which is of great value to the uncooled IR imaging systems in practical applications.

Comparison of tungsten films grown by CVD and hot-wire assisted atomic layer deposition in a cold-wall reactor

In this work, the authors developed hot-wire assisted atomic layer deposition (HWALD) to deposit tungsten (W) with a tungsten filament heated up to 1700–2000 °C. Atomic hydrogen (at-H) was generated by dissociation of molecular hydrogen (H2), which reacted with WF6 at the substrate to deposit W. The growth behavior was monitored in real time by an in situ spectroscopic ellipsometer. In this work, the authors compare samples with tungsten grown by either HWALD or chemical vapor deposition (CVD) in terms of growth kinetics and properties. For CVD, the samples were made in a mixture of WF6 and molecular or atomic hydrogen. Resistivity of the WF6-H2 CVD layers was 20 μΩ·cm, whereas for the WF6-at-H-CVD layers, it was 28 μΩ·cm. Interestingly, the resistivity was as high as 100 μΩ·cm for the HWALD films, although the tungsten films were 99% pure according to x-ray photoelectron spectroscopy. X-ray diffraction reveals that the HWALD W was crystallized as β-W, whereas both CVD films were in the α-W phase.

Photodegradation of methylene blue using magnetically reduced graphene oxide bismuth oxybromide composite

A magnetically reduced graphene oxide–bismuth oxybromide (MRGO–BiOBr) composite was successfully synthesized and found to possess magnetic, adsorptive and photocatalytic properties. The synthesized composite have been characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray Diffraction (X-RD), Scanning electron microscopy (SEM) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). Presence of FeO bond stretching vibrations and bromo compounds have been confirmed using FT-IR and the diffraction peaks of the composite obtained from X-RD showed a combination of peaks of both MRGO and BiOBr. SEM images further confirmed the presence of minute flakes of BiOBr scattered onto the surface of MRGO. Reduction in band gap energy from 2.76eV for pure BiOBr to 1.91eV for the composite was determined using UV–vis DRS. Photocatalytic degradation of Methylene Blue dye under visible light irradiation (150W Tungsten filament lamp) was examined using MRGO–BiOBr and around 96.84% of dye of 50ppm was degraded in 2h. Kinetic studies were done by splitting the kinetic data into 2 regions at 30min of irradiation and using the Langmuir–Hinshelwood (L–H) model to determine the rate constants. The composite was found to be easily separable in the presence of a magnet and on regeneration, studies showed no significant decrease in the photocatalytic activity of the composite even after 3 runs.

Photocurrent in Strontium Titanate Films on Silicon Substrates

Using the sol-gel method, strontium titanate films were prepared (strontium titanate xerogels) on monocrystalline silicon substrates at 750°C annealing temperature. Nickel upper electrodes were deposited by magnetron sputtering, and the current–voltage characteristics were measured for the prepared structures with two upper electrodes and a Schottky barrier. Significant changes in the current–voltage characteristics were observed after illuminating the diode structure with a halogen lamp characterized by 57 mW/cm2 intensity and 3123°C color temperature of the tungsten filament. For a 65-nm thick strontium titanate film under reverse bias voltage of –3 V the photocurrent is 80 μA, whereas without illumination the reverse current is close to zero. Under direct illumination and a voltage of 3 V the photocurrent is 190 μA, while without illumination the current does not exceed 22.5 μA.

Different approaches to modeling the LANSCE H⁻ ion source filament performance.

An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H(-) surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K-2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz-120 Hz.

The Hydrogen Plasma Effect on the Tungsten Oxide Nano-Sheets in Tokamak

In this research, the IR-T1 Tokamak plasma effect on tungsten oxide (WO3) nano-sheets has been investigated. For this purpose we deposited WO3 on stainless steel 316L (S.S.316L) via hot filament chemical vapor deposition method with hot tungsten filament in temperature 1800 °C. So, S.S.316L and WO3 sample installed on IR-T1 chamber and exposed to 300 shots of hydrogen plasma with a total duration of 11 s. For investigation of hydrogen plasma effects on crystalline structure properties, the X-ray diffraction (XRD), atomic force microscope (AFM), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy analysis was performed. It observed the some small changes in the position and intensity of XRD peaks therefore the plasma can affect the crystalline structure properties of WO3. The comparison of FESEM images of WO3 sample and S.S.316L show that WO3 has the least morphology defect against plasma shots as we can observe a crack with length around 100 μm on S.S.316L surface while WO3 surface was smoothed and didn’t create any defect, significantly. Also, the AFM analysis of WO3 shows the least evolutions of surface roughness.

Optimization techniques for improving the precision of isotopic analysis by thermal ionization mass spectrometry, taking strontium, neodymium, lead, and osmium as examples

ABSTRACTSeveral optimization techniques have been suggested to improve the signal and precision of analyses by thermal ionization mass spectrometry. Our work shows that tungsten filament is likely the most efficient for ionizing strontium when selecting from tungsten, rhenium, and tantalum filament. Deviations of isotopic ratios could be due to the degradation of the Faraday cups. This disadvantage could be avoided through eliminating the imperfect cup from the cup configuration. The high background produced from usage of rhenium filament could be decreased by cleaning the ion source and baking the source housing.

Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics.

The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. When the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8-12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa).

Failure Analysis of Filaments of Quadrupole Mass Spectrometer for Plasma Process Monitoring

A failure analysis of tungsten filaments used in quadrupole mass spectrometer for plasma process monitoring was carried by using SEM and EDS. Failed at high temperature, filaments showed two kinds of failure modes. The one is that diameter of filament became thinner gradually and finally snapped. The other is that filament abruptly snapped almost at a right angle. The EDS analysis showed Fe and C, including W and Fe, on the surface of failed filament. when failed filaments were treated with plasma in mixture of Ar and <TEX>$CF_4$</TEX>, the amount of Fe and C decreased. The failure analysis of filament showed that the cause of filament failure is thermal evaporation and grain growth of tungsten at high temperature.

Fabrication via Ultrasonication and Study of Silicon Nanoparticles

AbstractPhotoluminescent porous silicon (PSi) were prepared by an electrochemical etch of n-type silicon under the illuminationwith a 300 W tungsten filament bulb for the duration of etch. The red photoluminescence emitting at 620 nm with anexcitation wavelength of 450 nm is due to the quantum confinement of silicon nanocrystal in porous silicon. As-preparedPSi was sonicated, fractured, and centrifuged in toluene to obtain photoluminescence silicon quantum dots. BET and BHJmethods were employed to study the specific surface area of as-prepared PSi. Optical characterization of redphotoluminescent silicon nanocrystal was investigated by UV-vis and fluorescence spectrometer. Also SEM and TEMimages of porous silicon and nanoparticles were investigated.Keywords: Silicon Nanoparticle, Electrochemical Etching, Porosity, Ultrasonication 1. Introduction Since the discovery of photoluminescent porous sili-con (PSi) [1] it has been gaining growing popularity andgreat potential in chemical sensor

フィラメント電極を用いたマイクロ放電現象

Sub-millimeter sized DC discharge was experimentally investigated in the range of glow region, glow-arc transition region and arc region with use of the newly developed filament electrode and high voltage power source. The filament electrode consists of the pointed tungsten electrode electrolytic-polished and filament part. The current-voltage characteristics of the micro-discharge in the current range of 15 mA to 800 mA was investigated for various curvature radii of electrode tips. And the discharge appearances and anode melt spots were observed. It was found that the arc region shifts to the smaller current by using the cathode having sharpened tip. And the micro-discharge is concentrated by using pointed cathode with heating. So, the glow mode discharge with the current of 17 mA makes melt spots at the anode surface of stainless steel.

Lyman Alpha Photometer: a far-ultraviolet sensor for the study of hydrogen isotope ratio in the Martian exosphere

The Lyman Alpha Photometer (LAP), developed for flight on the Mars Orbiter Mission (MOM) spacecraft in 2013, is primarily designed to measure deuterium to hydrogen abundance ratio of the Martian exosphere over a 6-month period from a 263 km × 71,358 km elliptical orbit around Mars. A set of ultrapure (99.999%) hydrogen and deuterium gas-filled cells comprising tungsten filaments, a 25 mm diameter collection lens and a solar-blind photomultiplier tube together with an 8 nm bandpass Lyman alpha filter are the principal electro-optical assemblies of the instrument. This article presents scientific objectives of LAP and its performance specifications along with details of instrument design. The ground characterization techniques to assess LAP operational performance are also presented. End-to-end test results and evaluation matrix of LAP were satisfactory, well within the desired specifications. The first LAP onboard operation was carried out during the cruise phase of MOM spacecraft journey to verify its functionality and all recorded on-board health parameters were satisfactory.

Chemical nature of active sites for defect‐mediated nucleation on silicon dioxide

Germanium nanoparticle growth on SiO2 proceeds via defect‐mediated nucleation and particle density can be enhanced by chemically treating the SiO2 with SiHx. The influence of SiHx fragments on SiO2 surface sites is studied using a fluorescent probe‐based technique to understand the chemical nature of the inherent defect trapping sites and the chemical nature of the additional trapping sites formed by SiHx. Oxygen‐vacancy sites on SiO2 are the inherent sites for defect‐mediated nucleation. SiHx fragments, generated by cracking disilane on a hot tungsten filament, are shown to react with strained siloxane sites, leading to a conversion of these strained siloxane sites into a different low density defect site that is shown to display reactive characteristics similar to the oxygen‐vacancy defect sites. Previous work demonstrating an increased density of Ge nuclei on SiO2 surfaces with increasing SiHx exposure is interpreted in the context of the current experimental results. © 2015 American Institute of Chemical Engineers AIChE J, 62: 367–372, 2016

A New Hydrogen-Producing Strain and Its Characterization of Hydrogen Production.

A newly isolated photo non-sulfur (PNS) bacterium was identified as Rhodopseudomonas palustris PB-Z by sequencing of 16S ribosomal DNA (rDNA) genes and phylogenetic analysis. Under vigorous stirring (240rpm), the hydrogen production performances were greatly improved: The maximum hydrogen production rate and cumulative hydrogen production increased by 188.9 ± 0.07 % and 83.0 ± 0.06%, respectively, due to the hydrogen bubbles were immediately removed from the culture medium. The effects of different wavelength of light on hydrogen production with stirring were much different from that without stirring. The ranking on the photo-hydrogen production performance was white > yellow > green > blue > red without stirring and white > yellow > blue > red > green under stirring. The best light source for hydrogen production was tungsten filament lamp. The optimum temperature was 35°C. The maximal hydrogen production rate and cumulative hydrogen production reached 78.7 ± 2.3ml/l/h and 1728.1 ± 92.7mol H2/l culture, respectively, under 35°C, 240rpm, and illumination of 4000lux. Pyruvate was one of the main sources of CO2 and has a great impact on the gas composition.

Synthesis and characterization of large WO3 sheets synthesized by resistive heating method

A simple, low-cost method is presented to grow tungsten oxide large sheets simply by resistively heating a pure tungsten filament under air/water vapor flow. The obtained structures were studied using scanning and transmission electron microscopy, selected area diffraction, X Ray diffraction, Raman and X-ray photoelectron spectroscopy, photoluminescence and zeta potential measurements. SEM observations revealed that sheets formed by broadening of the wires/belts over longer growth period. Photoluminescence measurements showed that tungsten oxide sheets had an intense visible emission band.

오염된 QMS의 원인 분석과 세정 및 기능 복원

Quadrupole Mass Spectrometers (QMS) is a very useful tool in vacuum process diagnosis. Tungsten filament based ion sources are vulnerable to contamination from process gas monitoring. Common symptoms of quadrupole mass spectrometer malfunction is appearance of unwanted contaminant mass peaks or no detection of any ion peaks. We disassembled used quadrupole mass spectrometer and found out black insulating deposits on inside of ion source parts. Five steps of cleaning procedure were applied and almost full restoration of functions were confirmed in two types of closed ion source quadrupole mass spectrometer. By using a numerical modeling (CFD-ACE+) technique, the electric potential profile of ion source with/without insulating deposit was calculated and showed the possibility of quadrupole mass spectrometer malfunction by the deterioration of designed potential profile inside the ion source.