Showing papers on "Tungsten published in 1973"
TL;DR: Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of 2,2-dimethylpropane to 2-methylbutane.
Abstract: Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of 2,2-dimethylpropane to 2-methylbutane. This catalytic behavior, which is typical of platinum, is not exhibited at all by tungsten. The surface electronic properties of the latter are therefore modified by carbon in such a way that they resemble those of platinum.
1,738 citations
211 citations
TL;DR: In this article, it was shown that WO 3 γ-Al 2 O 3 cannot be appreciably reduced in hydrogen at 550 °C, whereas WO3 SiO 2 is reduced to lower valence states and unsupported wO 3 is completely reduced to tungsten metal under these conditions.
171 citations
TL;DR: In this paper, the X-ray photoelectron spectroscopy (ESCA) has been used in a study of CO and O2 chemisorbed on polycrystalline tungsten sample.
103 citations
TL;DR: The structure of D 0.53 WO 3 has been determined by a room temperature powder neutron diffraction study as discussed by the authors, and the unit cell is body centered cubic ( Im 3) and contains 8 formula weights ( a = 7.562 ± 0.002 A).
102 citations
TL;DR: In this article, the progress made at Cornell University over the past few years in applying the field ion microscopy (FIM) technique to the study of point defects in irradiated or quenched metals is reviewed.
Abstract: The progress made at Cornell University over the past few years in applying the field ion microscopy (FIM) technique to the study of point defects in irradiated or quenched metals is reviewed. The techniques involve essentially the atom by atom dissection of specimens by pulse field evaporation and the corresponding recording on film of the extensive number of FIM images produced at each stage of the process. The application of these techniques to the following problems are discussed: (i) the mobility of self interstitial atoms (SIA) in substage IE of irradiated tungsten and platinum, (ii) the geometric configuration of the SIA, (iii) the point defect structure of depleted zones in tungsten and (iv) the properties of monovacancies and divacancies in quenched platinum.
95 citations
TL;DR: The rate of reaction between Si (100) surfaces and tungsten films deposited by rf diode sputtering depends on the preparation of the silicon surface and the native oxide layer that exists when sputter cleaning is not used as discussed by the authors.
Abstract: The rate of reaction between Si (100) surfaces and tungsten films deposited by rf diode sputtering depends on the preparation of the silicon surface. If rf substrate bias is used to clean the silicon, then the rate of reaction in the temperature range 700–850 °C is independent of time, with an activation energy of 3 eV/mole W. The native oxide layer between the silicon and tungsten, that exists when sputter cleaning is not used, can act as a barrier to WSi2 formation. In this case, the time‐independent region is preceded by a period when the reaction rate increases with time. The rate is then controlled by two‐dimensional spreading of discontinuous WSi2 regions that originate at sites where the reaction barrier can be penetrated. After a continuous WSi2 layer is formed, additional growth can produce a stage where the increased path length for silicon diffusion causes the transport step to control the over‐all rate of the reaction. Quantitative models are presented for each of the three stages in the reaction. The models explain some of the macroscopic observations made on reacted layers.
94 citations
90 citations
83 citations
TL;DR: The interaction of three equivalents of methyl-lithium with tungsten hexachloride in diethyl ether gives a brown solution from which hexamethyltungsten can be isolated as discussed by the authors.
Abstract: The interaction of three equivalents of methyl-lithium with tungsten hexachloride in diethyl ether gives a brown solution from which hexamethyltungsten can be isolated. The chemical and spectroscopic properties of the compound are described. Reaction with nitric oxide gives tetramethylbis(N-methyl-N-nitrosohydroxylaminato)tungsten(VI) which is shown by n.m.r. studies to be stereochemically non-rigid at room temperature.
81 citations
TL;DR: In this article, a surface ionization ion source is described, which operates by heating a capped tungsten crucible to 2800-3300°C by electron bombardment.
TL;DR: In this article, the enthalpies of two hydrogen tungsten bronze phases H0.35WO3 (H2(g) and WO3(s) at 298.15 K were determined by solution calorimetry.
TL;DR: In this article, the effects of the properties of lowvoltage triode sputtered tungsten films on internal stress and resistivity were investigated in the presence of 1 μ argon pressure at rates in the range of 50-400 A/min.
Abstract: The continuing development of microelectronic circuits toward greater complexity has stimulated interest in new materials and processes compatible with the currently known silicon device technology. Tungsten has been considered as the first‐level conductor for a multilevel structure due to its relatively low electrical resistivity, its thermal expansion coefficient which matches fairly well to that of silicon, its demonstrated good adherence to the dielectrics of interest, and its ability to withstand high‐temperature processing. The present work is a part of a study of the dependence of the properties of low‐voltage triode sputtered tungsten films upon deposition parameters. The effects on internal stress and resistivity of tungsten films are reported here. Tungsten films have been deposited with thicknesses from 1000 to 15000 A and with resistivities as low as 8 μω cm (1.55 of the bulk). These films were deposited at 1 μ argon pressure at rates in the range of 50–400 A/min. The electrical resistivity wa...
TL;DR: In this article, the field dependence of the total current is accurately described by a simple theory of barrier penetration, and the field emission of hot electrons is observed from a laser-illuminated tungsten tip.
Abstract: Field emission of hot electrons is observed from a laser-illuminated tungsten tip. The field dependence of the total current is accurately described by a simple theory of barrier penetration.
TL;DR: In this article, the infrared spectrum of chemisorbed α-CO on polycrystalline tungsten has been studied using ultrahigh vacuum techniques, and the αCO state has been spectroscopically resolved into two states.
TL;DR: The ternary alloy system Ti-W-C was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction, and metallographic techniques on hot-pressed and heat-treated, alloy specimens and a phase diagram from 1500 °C through the melting range established as discussed by the authors.
Abstract: The ternary alloy system Ti-W-C was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction, and metallographic techniques on hot-pressed and heat-treated, as well as melted, alloy specimens and a phase diagram from 1500 °C through the melting range established. Above 2530 °C, titanium monocarbide and the isomorphous cubic high temperature phase in the W-C binary system are completely miscible and the solid solution has a congruent (maximum-type) melting point of 3130 °C at the approximate composition (Ti0.54W0.44)C0.75. Below 2530 °C, the tungsten exchange in the cubic monocarbide is temperature-dependent and decreases to about 50 at.% at 1400 °C. The titanium exchange in W2C is less than 3 at.% at 1500 °C and reaches a maximum of 8 at.% at 2680 °C. In addition to the ternary congruent melting point, four reaction isotherms occur in the system: Two are pseudobinary eutectics, monocarbide + graphite at 3030 °C, and monocarbide + tungsten-rich metal alloy at 2700 °C; peritectic melting of the binary WC results in a class II reaction L + C⇄cubic monocarbide + WC(hex) at 2760 °C, and a fourth isotherm at 2680 °C is associated with a ternary eutectic between metal, monocarbide (B1), and W2C. Pseudobinary eutectic melting between the monocarbide and the metal phase is directly attributable to the large stability difference between titanium and tungsten carbide, and the measured tie line distribution in the two-phase range metal + monocarbide is in accordance with estimates from known thermodynamic values for the binary boundary phases. The phase behavior in pseudobinary monocarbide solutions is largely determined by the relative lattice size of the boundary carbides, except for systems (M, W)C1 − x (M = Ti, Zr, Hf, V). which show extra stabilization due to bonding effects.
TL;DR: In this article, a calibrated LiF crystal spectrograph recorded the radiation spectrum in the 3 − to 25 − kV range by exploding wire discharges of tungsten and titanium driven by a high power pulse generator.
Abstract: Exploded‐wire discharges of tungsten and titanium driven by a high‐power pulse generator have been used to produce intense x‐ray continuum and line radiation. A calibrated LiF crystal spectrograph recorded the radiation spectrum in the 3‐ to 25‐keV range. More than 20 J of x radiation are emitted in this photon energy band by tungsten plasmas in less than 50 nsec. The source of emission is less than 1 mm in diameter and about 3.5 cm long.
TL;DR: In this article, the optical properties of the alkali metal tungsten bronzes are investigated and a review of existing data and the interpretation thereof is presented; the interpretation of optical constants is based on an existing band structure for ReO 3 and modifications thereto are suggested.
TL;DR: In this article, absolute coverages and sticking coefficients as functions of both gas and surface temperatures are presented for CO adsorption on the (110) plane of tungsten, showing that initial sticking coefficients drop with increasing gas or surface temperature but eventually level off at ~ 0.5.
ESRO1
TL;DR: In this article, the electronic energy levels of hydrogen adsorbed on three low-index planes of tungsten have been studied by a directional photoemission technique for coverages between 0.01 and 1 monolayer.
Abstract: The electronic energy levels of hydrogen adsorbed on three low-index planes of tungsten have been studied by a directional photoemission technique for coverages between 0.01 and 1 monolayer. A number of relatively sharp resonance levels are observed, which show half-widths down to 0.5 eV. For the (100) face, a single high-coverage state evolves from multiple low-coverage states, while on the (110) face two states appear to build up sequentially. No pronounced coverage dependence is observed for the (111) face.
TL;DR: In this article, a correlation between changes in the film structure occurring with coverage and features of the work function and adsorption heat concentration dependences was found, and it was concluded that interaction between lithium adatoms on W(112) is highly anisotropic.
TL;DR: In this paper, a reduction of WO3 single crystals was carried out in terms of proton diffusion to give an activation energy of about 16 kJ mole−1 and a correlation time preexponential factor of about 70 nsec for the process.
TL;DR: In this paper, the chemisorption of formaldehyde at ~100 K has been investigated on two single crystal planes of tungsten, W(100) and W(111).
TL;DR: In this article, a tungsten surface by adsorbed layers of gold, silver and copper has been studied by field emission and field ion microscopy, and it was shown that the capacity of an adsorbate to reconstruct the substrate is related to the strength of the adsorbates-substrate bond.
TL;DR: In this paper, the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices was investigated.
Abstract: We have investigated the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices. The apparatus consisted of a sputter-ion pumped 18-in. diam UHV station, 6-kW e gun, and a quartz crystal rate monitor. The evaporation process employs low background pressures (1−3×10−7 Torr), substrate heating (200–700 °C), a preevaporation step, and evaporation at rates of 100–500 A/min. Maximum throughput is 16 1(14)-in. diam silicon slices per run. Using substrate temperatures of 500–700 °C, we have been able to produce mechanically stable, adherent films having a resistivity of 7–8 μΩ cm and a sheet resistance of ∼ 0.08 Ω/□ (for 9000-A film). “Cold”-deposited films (> 1000 A thick) having a high resistivity of 40–50 μΩ cm can be annealed at 1000 °C to resistivity of 10–15 μΩ cm. The films are single-phase bcc W with a small grain size of 0.1–0.2 μ. Low resistivity films (deposited above 550 °C) are associated with a large degree of microstructural perfection, and have small tensile stresses (3−7×109dyn cm−2). The films possess, excellent high-resolution etchability, and were found to be compatible with MOS structures provided care is exercised during the deposition.
TL;DR: In this paper, the anodic oxidation of hydrogen on platinized boron carbide and supports was investigated and it was shown that the effective reaction zone area is extended onto the support, increasing the net electrode current.
Abstract: Electrochemical measurements on the anodic oxidation of hydrogen on platinized boron carbide and supports reveal that the latter is an "active" support, participating directly in the over‐all electrode reaction. In contrast, boron carbide is an "inert" support and takes no part in the electrode reaction. This work and previous investigations on the composition of the , confirm that the electrode reaction proceeds by the formation and oxidation of hydrogen tungsten bronzes In this way the effective reaction zone area is extended onto the support, increasing the net electrode current.
TL;DR: In this article, the relative bonding energies of nitrogen chemisorbed at three symmetric sites on a W(100) surface, represented by finite arrays of tungsten atoms, were obtained by means of the extended Huckel molecular orbital theory (EHMO).
Abstract: The relative bonding energies of nitrogen chemisorbed at three symmetric sites on a W(100) surface, represented by finite arrays of tungsten atoms [L. W. Anders. R. S. Hansen, and L. S. Bartell, J. Chem. Phys. 59, 5277 (1973)] were obtained by means of the extended Huckel molecular orbital theory (EHMO). The preferred site for nitrogen chemisorption was found to be the five coordination number (5 CN) site or the fourfold site with a tungsten atom below four tungsten atoms surrounding the nitrogen atom. The 5p orbital repulsive energy, in the case of hydrogen chemisorption, could be adequately approximated by the sum over pairs of empirical exponential repulsive terms; in the case of nitrogen chemisorption, this same method was approximately 10% in error at the equilibrium bond distance, and repulsive energies were therefore obtained from calculations including tungsten 5p orbitals but with smaller arrays.