Showing papers on "Tungsten published in 1984"

Femtosecond Laser Interaction with Metallic Tungsten and Nonequilibrium Electron and Lattice Temperatures

Abstract: High-intensity, 75-fs optical pulses have been applied to observe multiphoton and thermally enhanced photoemission from a tungsten metal surface. Experimental results suggest the presence of anomalous heating, a transient nonequilibrium temperature difference between the electrons and lattice. Pump-probe measurements indicate an electron-phonon energy relaxation time of several hundred femtoseconds.

Selective Low Pressure Chemical Vapor Deposition of Tungsten

Abstract: We have examined the kinetics of low pressure chemical vapor deposition of tungsten by the hydrogen and silicon reduction of within a pressure range of 0.1–5 torr and a temperature range of 250°–500°C. The rate‐limiting mechanism for the hydrogen reduction system was determined to be the dissociation of adsorbed on the surface, with an activation energy of 0.71 eV. A self‐limiting deposit results from the reaction, the thickness and structure of which are dependent upon the initial native oxide characteristics. Deposition occurs selectively on materials that react directly with or yield monatomic hydrogen. In the presence of hydrogen, the degree of selectivity is a function of temperature, substrate material, and surface cleanliness.

Data Compendium for Plasma-Surface Interactions

Abstract: A review of particle-solid processes pertinent to modelling plasma-wall interactions is presented, and sets of recommended data are given. Analytic formulas are used where possible; otherwise, data are presented in the form of tables and graphs. The incident particles considered are e−, H, D, T, He, C, O, and selfions. The materials include the metals aluminum, beryllium, copper, molybdenum, stainless steel, titanium, and tungsten and the nonmetals carbon and TiC. The processes covered are light ion reflection, hydrogen and helium trapping and detrapping, desorption, evaporation, sputtering, chemical effects in sputtering, blistering caused by implantation of helium and hydrogen, secondary electron emission by electrons and particles, and arcing.

The behaviour of tungsten in granitic melt-vapour systems

Abstract: An experimental study has been carried out to determine the effect of solution composition on the partitioning behaviour of tungsten in granitic melt-vapour systems at 800° C and 1 kbar With chloride and phosphate solutions, tungsten partitions strongly into the aqueous phase, whereas with fluoride, carbonate and borate solutions, and water alone, tungsten partitions in favour of the melt With chloride solutions, the fluid/melt partition coefficients (K D) for W show a marked positive correlation with chloride concentration, and suggest that at low chloride concentrations W-Cl complexes with low Cl∶W ratios (such as associated equivalents of (WO3)2C1−) may be present In contrast, at higher chloride concentrations complexes with high Cl∶W ratios (such as WOCl4, WCl6 and associated ionic equivalents) may predominate With phosphate solutions, K D shows little variation with phosphate concentration, and phosphorus heteropolytungstates (such as H3[PW12O40]) may be present There is no evidence to suggest that fluoride, carbonate or borate complexes of tungsten are important under the experimental conditions: the data for these compositions can be interpreted assuming that isopolytungstates (such as H6[H2W12O40]) are present Within high temperature hydrothermal solutions tungsten may be transported principally as isopolytungstates and heteropolytungstates in addition to chloride complexes, and this may, in part, account for the common association of apatite and arsenopyrite with scheelite and wolframite in tungsten deposits

Physical and electrochromic properties of the amorphous and crystalline tungsten oxide thick films prepared under reducing atmosphere

Abstract: The physical and electrochemichromic properties of the amorphous and crystalline tungsten oxide films prepared by thermal evaporation of WO3 powder under a reducing atmosphere have been investigated. The oxide films with 850–24 500 A thick were deposited on the substrates maintained at a temperature ranging from 50 to 500 °C under a vacuum below 1×10−5 Torr. Properties of the oxide films formed depend considerably on the deposition temperature. The as‐prepared oxide films formed at a temperature higher than 400 °C have a resistivity of 10−3−10 Ω cm, and are blue colored, and mainly composed of crystalline WO3. The oxide films formed at a temperature lower than 350 °C have a resistivity of 105–109 Ω cm, and are transparent and amorphous. Both of the amorphous and crystalline oxide films have good electrochemichromic properties. From x‐ray analysis, the crystalline WO3 thick films were found to change to hydrogen tungsten bronze films with a chemical composition of H0.33WO3 during electrochemical coloration...

In situ stress measurement of refractory metal silicides during sintering

Abstract: The stress of thin film tantalum silicide, titanium silicide, and tungsten silicide was measured in situ during sintering. These refractory metal silicide films were cosputtered on oxidized silicon, quartz, and sapphire substrates. The films were heated to 910 °C, annealed for 30 min, and cooled down to room temperature. Throughout the heat treatment cycle, the film stress was measured at short intervals by measuring the curvature of the film/substrate couple with a laser beam. It was demonstrated that the intrinsic stress of these silicides is negligible at 910 °C. The final room temperature stress of these silicides, after high temperature sintering, is mainly thermal stress which originates from the difference in thermal expansion coefficients between the films and the substrates. The final stress ranged from 8×108 to 2×109 Pa depending on the silicide and the substrate material. The biaxial elastic moduli were found to be 3.4×1011 Pa for TaSi2.4, 3.9×1011 Pa for TaSi1.4, and 2.2×1011 Pa for TiSi2.4. T...

Fracture Behavior of W-Ni-Fe Heavy Alloys

Abstract: Heavy alloys were liquid phase sintered from compacts of mixed W, Ni, and Fe powders. The alloy compositions ranged from 93 to 97 wt pct W, with the Ni:Fe ratio maintained at 7:3. Sintering was performed under hydrogen in the 1465 to 1485 °C temperature range, giving full density within the first 15 minutes. The room temperature strength and ductility showed major degradation with sintering times in excess of two hours. Tensile tests and bend tests have been performed to isolate the fracture mode and the property determining features. Initial cracking occurs at the tungsten-tungsten grain boundaries and in the tungsten grains. These latter cracks propagate through the structure to give eventual failure. The ductility to failure is shown to be governed by the strength of the tungsten-matrix interface. The maximum elongation depends on the contiguity, which in turn is set by the alloy composition.

EXAFS studies of amorphous molybdenum and tungsten trisulfides and triselenides

Abstract: lower freezing point of N 2 relative to argon, and hence a slightly slower rate of freezing during the deposition process and slightly greater mobility of the reactant species. It is also interesting to note that a recent study2 of the S 0 2 / H 2 0 system found the large majority of the sulfur either in the form of SO2 or as S2052-, while very little of the intermediate SO3,was noted. The disulfite S205,anion might form by one of several routes under these conditions. One is the simultaneous, three-body collision of two SO2 molecules and T120, but this is quite unlikely at the concentrations employed. More likely, formation of S2052involves initial formation of the SO3,anion, followed by addition of a second SO2 unit to form the final product anion. The fact that the ‘*O label appears in the bridging position as well as in the terminal oxygen positions is consistent with this view as well. If this is the mechanism by which S20,2is formed, then the addition of SO, to SO3,must be very facile, with effectively no activation energy, since in many cases nearly all of the SO3,is converted to S2052during the condensation process. A final possible mechanism, the reaction of T120 with sulfur dioxide dimer, (SO,),, cannot be ruled out but does not seem likely in that this dimer is weakly bound and should not be abundant a t the concentrations employed. Conclusions

Electrode for medical applications

Abstract: In order to expand the availability of effective and usable electrodes for medical applications, an electrode is proposed which is comprised of an electrically conductive carrier material and of a porous layer in its active region which is composed of a carbide, nitride or carbonitride of one of the metals titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum or tungsten.

Diffusivity of 3He atoms in perfect tungsten crystals

Abstract: The diffusivity of 3He atoms in perfect crystals of tungsten has been studied employing the atom‐probe field‐ion microscope (FIM) technique. Tungsten FIM specimens were implanted in situ with 300‐eV 3He+ ions, to a fluence of 3×1015 ions cm−2, at specimen temperatures which ranged from 60 to 110 K. The 3He+ ion beam was analyzed magnetically and the ion source was connected to the atom probe through a differentially pumped aperture. At an implantation energy of 300 eV no radiation damage was produced by the implanted 3He atoms. Thus, the state of a tungsten specimen after an implantation consisted of 3He atoms with an initial depth distribution that was determined solely by the range profile of the low‐energy ions. Isothermal annealing experiments between 90 and 110 K were employed to study the kinetics of recovery of the implanted 3He atoms; at 60 K the 3He atoms are immobile. This data, in combination with a suitable diffusion model, was used to determine—for the first time—the diffusivity [D3He(T)] and...

Low resistivity tungsten silicon composite film

Abstract: A composite film is provided which has a first layer of WSix, where x is greater than 2, over which is disposed a second layer of a tungsten complex consisting substantially of tungsten with a small amount of silicon therein, typically less than 5%. Both layers are deposited in situ in a cold wall chemical vapor deposition chamber at a substrate temperature of between 500° and 550° C.. Before initiating the deposition process for these first and second layers, the substrate onto which they are to be deposited is first plasma etched with NF3 as the reactant gas, then with H2 as the reactant gas, both steps being performed at approximately 100 to 200 volts self-bias. WSix is then deposited onto the surface of the substrate using a gas flow rate for silane which is 20 to 80 times the flow rate of tungsten silicide, followed by deposition of a tungsten complex as the second layer, using a gas flow rate for tungsten hexafluoride which is 1 to 3 times the flow rate of silane, and a gas flow rate of hydrogen which is about 10 times the flow rate of silane. Similarly, in another embodiment, the tungsten complex without the silicide layer is deposited directly onto a silicon surface using the same process as for the tungsten complex in the second layer of the first embodiment.

A new tungsten gate process for VLSI applications

Abstract: In spite of the growing demand for MOS gates and interconnections of higher conductivity, the refractory metal gate process has not received as much attention as those using silicides because it is incompatible with the Si-gate process. The metal gate cannot withstand oxidizing annealing ambients, and source-drain formation by ion implantation is difficult because of the channeling of doping ions through the gate metal during ion implantation. In a new process developed for use in MOS VLSI fabrication, tungsten (W) is used as a gate metal because degradation of SiO 2 by annealing the metal/SiO 2 /Si structure at around 1000°C can be minimized if the metal is W. Metal oxidation is prevented by using a H 2 /H 2 O ambient for this annealing, which also allows Si to be oxidized in the same ambient. The channeling mentioned above is stopped by forming a thin layer of PSG or WO x on the W. This gate process is believed to be a step forward toward the desired compatibility.

Process for depositing a low resistivity tungsten silicon composite film on a substrate

Abstract: A composite film is provided which has a first layer of WSix, where x is greater than 2, over which is disposed a second layer of a tungsten complex consisting substantially of tungsten with a small amount of silicon therein, typically less than 5%. Both layers are deposited in situ in a cold wall chemical vapor deposition chamber at a substrate temperature of between 500° and 550° C. Before initiating the deposition process for these first and second layers, the substrate onto which they are to be deposited is first plasma etched with NF3 as the reactant gas, then with H2 as the reactant gas, both steps being performed at approximately 100 to 200 volts self-bias. WSix is then deposited onto the surface of the substrate using a gas flow rate for silane which is 20 to 80 times the flow rate of tungsten silicide, followed by deposition of a tungsten complex as the second layer, using a gas flow rate for tungsten hexafluoride which is 1 to 3 times the flow rate of silane, and a gas flow rate of hydrogen which is about 10 times the flow rate of silane. Similarly, in another embodiment, the tungsten complex without the silicide layer is deposited directly onto a silicon surface using the same process as for the tungsten complex in the second layer of the first embodiment.

Ferroelectric properties of tetragonal tungsten bronze single crystals

Abstract: Ferroelectric tetragonal tungsten bronze (T.B.) family single crystals, e.g., SBN, BSKNN, KLN, SKN and PBN, have been grown and their ferroelectric properties have been investigated. The results show that the dielectric, piezoelectric, and electromechanical coupling coefficients are significantly large for these crystals; however, they are markedly different when going from smaller to bigger unit cell T.B. crystals. For example, e33 and d33 are substantially larger for the smaller unit cell T.B. crystals, e.g., SBN and SKN, while e11 and d15 are dominant for bigger unit cell bronzes. However, these differences do not have such a significant effect on the respective electro-optic and pyroelectric properties.

Comparison of laser-initiated and thermal chemical vapor deposition of tungsten films

Abstract: ArF excimer laser radiation has been used to deposit W films on silicon and on SiO2 by initiating the gas phase reaction of WF6 with H2 Deposition rates >100 nm/min and film resistivities as low as two times the bulk value have been obtained at deposition temperatures of 440 °C The properties of the laser‐deposited films are compared with those of fims obtained using conventional thermal deposition techniques Film resistivity correlates with the microstructure which in turn depends on the deposition temperature; above 350 °C the low‐resistivity α‐W phase dominates

Plasma‐enhanced chemical vapor deposition of β‐tungsten, a metastable phase

Abstract: Plasma‐enhanced chemical vapor deposition of a metastable phase of tungsten ( β‐W) is performed using tungsten hexafluoride and hydrogen as source gases. At 350 °C, the as‐deposited resistivity of these films is ∼50 μΩ cm. After heat treatments between 650 and 750 °C in forming gas, the resistivity drops below 11 μΩ cm. Concomitant with this resistivity change is a phase change to α‐W, the equilibrium, body‐centered‐cubic form.