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A method was developed for optimizing a cascade with two additional product streams, in which two components of intermediate mass are concentrated simultaneously. The solution of the optimization problem is based on variation of the cuts of partial flows of the cascade steps with large separation factors. A minimum of the total feed stream of the steps with specified concentration of the isotopes is used as the optimization criterion. A computational experiment on separation of a tungsten hexafluoride mixture was performed. It is shown that high concentration of intermediate components can be obtained with additional product streams exceeding the primary product and waste streams of the cascade.

We identify hydrolysis reaction mechanism of water-reactive WF6 and its accompanying intermediates using first-principles calculations. For the purpose, we evaluate activation and free energy diagrams of elementary reaction steps. We find that WF6, WOF4, and WO2F2 form stable adducts, which quickly reacts with H2O by substituting the ligand F. Gaseous WOF4, WO2F2, WO3 are predicted as unstable in the increasing order, but polymerization reduces their instability, leading to solidification. In overall reaction, WOF4 hydrolysis is the bottleneck due to significantly higher activation barrier of trans isomeric complex than cis counterpart.

A tungsten carbide coating was prepared by atmospheric chemical vapor deposition (CVD) with tungsten hexafluoride (WF6), hydrogen, and dimethyl ether (DME) as the reaction gases, under a dimethyl ether partial pressure (PDME) of 3.2–21.0 kPa and a temperature of 550–600 °C. The phase compositions of the coatings are W2C + W and W3C + W, and it is found that when PDME is low, the coating has a lamellar structure, but at a high PDME, the lamellar structure and fibrous tissue are simultaneously present in the scanning electron microscope (SEM) image. In the latter case, no delamination was found, which was visible at a low PDME. In addition, as the PDME increases, the deposition rate of the coating decreases, and ultimately, the coating cannot continue to grow. The growth model of the tungsten carbide coating based on the kinetics of the chemical vapor deposition of tungsten by the hydrogen reduction of tungsten hexafluoride was proposed, and the influences of PDME and temperature on the coatings were discussed and the orientation relationship between W and W2C in high resolution transmission electron microscopy (HRTEM) was analyzed.

Chemical vapor deposited (CVD) high-purity tungsten can be manufactured as electron emitters in thermionic fuel elements. Exposed surface planes of the emitter emit electrons and affect the efficiency and load capacity of the thermionic fuel element. In order to determine the electron emission planes of the emitter, the metallurgic structures, the preferred orientation and the as-deposited surface morphology of CVD tungsten have been investigated. In this work, high-purity (over 99.99%) tungsten was achieved by two different precursors: hydrogen reduction of tungsten hexafluoride (WF 6 ) and thermolysis of tungsten hexachloride (WCl 6 ). The microstructures of CVD tungsten were characterized by metallography analysis, X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and white light interference (WLI). Tungsten fabricated by hydrogen reduction of WF 6 and thermolysis of WCl 6 has ⟨100⟩-preferred columnar microstructures. However, the latter exhibits larger columnar grains and preferred ⟨100⟩ less. The preferred orientation is caused by the higher growth rate of the ⟨100⟩ orientation and competition between the ⟨100⟩ orientations of different grains. The as-deposited surface consists of tiny pyramids, with ⟨100⟩ axis and {111} side faces. In contrast to tungsten produced by hydrogen reduction of WF 6 , the pyramid on tungsten synthesized via thermolysis of WCl 6 contains small {110} facets on the four edges. Therefore, tungsten made via thermolysis of WCl 6 is a better candidate for thermionic fuel elements, because the higher work function of {110} planes enables better output efficiency.

Controlled thin film etching is essential for further development of sub-10 nm semiconductor devices. Vapor-phase thermal etching of oxides is appealing for achieving highly conformal etching of high aspect ratio features. We show that tungsten hexafluoride (WF6) can be used to selectively etch amorphous TiO2 films versus other oxides including Al2O3. Chemical vapor etching (CVE) of TiO2 by WF6 was studied with quartz crystal microbalance (QCM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and thermodynamic modeling. The XPS results show evidence for a WOxFy layer that forms on of the TiO2 films during the etch process, which may act as a surfactant layer to help enable fluorination of the TiO2. Direct CVE of TiO2 by WF6 is strongly temperature dependent, where etching proceeds readily at 220 °C, but not at T ≤ 170 °C. This is consistent with thermodynamic modeling showing that the etching rate is determined by the volatilization of metal fluoride and WF2O2 product species. We also ...

A fluoride cycle in tungsten technology is based on three processes: (i) electrochemical decomposition of HF in the KHF2 + HF melt at 80–100°C with the separate evolution of gaseous fluorine and hydrogen; (ii) fluorination of the tungsten powder with evoluated fluorine at 300–350°C with the condensation of formed WF6 in a liquid form at t = 2.5–3.0°C, and (iii) reduction of gaseous WF6 with evoluated hydrogen at t = 580–600°C with the condensation of formed HF at +1°C and its use for the fluorine and hydrogen production, thereby ensuring their recycling in the cycle. The optimization of mentioned processes resulted in hardware-process implementations providing the formation of a large-scale plane and cylindrical billets in the industrial scale for deformation, as well as pipes, crucibles, and other products of various sizes made of tungsten with productivity of one process line of ~4.3 kg/h (>34 t/yr) with the fulfillment of environmental requirements. In contrast with the methods of powder metallurgy, the described technology ensures the formation of dense half-finished products and products made of pure tungsten with finer grain structures and almost unlimited sizes. Herewith, the specific power consumption for 1 kg of production lowers by a factor of 2.0–2.5. To increase the production efficiency, the simultaneous operation of four process lines in an automated mode is recommended.

Tungsten deposition from a gaseous mixture of tungsten hexafluoride and hydrogen on the surface of a porous preform made of thoriated tungsten makes it possible to bond particles of peripheral layers and its core against each other, and create more plastic surface coating capable of relaxing stresses occurring during rotary forging, thus preventing destruction of semi-finished products. The described method made it possible to carry out rotary forging of the pilot batch consisting of insufficiently sintered preforms of thoriated tungsten which were previously destroyed if processed uncoated. The achieved improvement of technological properties may be used in the production of similar tungsten-based compositions (grade VL and VI), as well as for other types of deformation. The results can be applicable for the following: 1) Lowering the sintering-welding temperature of bars (and rods) made of dispersion-strengthened tungsten-based compositions, thus reducing power consumption and increasing the time between equipment overhauls; 2) Increasing the size of semi-finished products produced with the existing equipment, thus increasing the process productivity and expanding the range of output products; 3) Releasing less environmentally hazardous thoriated tungsten products, thus greatly reducing radiation exposure of operators; 4) Using composite cathodes in arc xenon lamps, thus increasing their operational life by 2–3 times.

The computational procedures to model the fluorination of the tungsten powder with fluorine and condensation of formed WF6, which describe the available experimental data satisfactorily, are developed using physicochemical foundations of processes. With their help, the equipment sizes and process parameters of the two-stage fluorination of the tungsten powder with fluorine with the condensation of liquid WF6 after each stage at 2.5–3.0°C are optimized. The possibility of fabricating WF6 with productivity of 5.23, 6.53, and 7.83 kg/h in reactors 200, 300, and 360 mm in diameter, respectively, at 300–350°C without the forced cooling of the highest heat-beat first fluorination setup is shown. The completeness of fluorine usage higher than 99.99% is attained in this case, while the amount of harmful gases (F2, WF6) leaving the process chain does not exceed their maximal permissible concentrations already in the vent gas volume. Recommendations for the organization of the fluorination production process of the tungsten powder are given.

The paper considers the process of reduction of gaseous tungsten hexafluoride with hydrogen to metallic tungsten using the chemical vapor deposition method (CVD) [1]. The essence of this method is that the final product is formed on the target substrate, as a result of the interaction of gaseous precursor substances or the thermolysis of the vapor of the precursor substance. On the basis of a complete diffusion model of the process of reducing gaseous tungsten hexafluoride with hydrogen, original boundary conditions were written on the substrate surface, which allowed us to obtain a closed system of second-order differential equations in partial derivatives representing the mathematical model of the process under study [2-5].

© 2018 American Chemical Society. When two-dimensional (2D) group-VI transition metal dichalcogenides such as tungsten disulfide (WS 2 ) are grown by atomic layer deposition (ALD) for atomic growth control at low deposition temperatures (≤450 °C), they often suffer from a nanocrystalline grain structure limiting the carrier mobility. The crystallinity and monolayer thickness control during ALD of 2D materials is determined by the nucleation mechanism, which is currently not well understood. Here, we propose a qualitative model for the WS 2 nucleation behavior on dielectric surfaces during plasma-enhanced (PE-) ALD using tungsten hexafluoride (WF 6 ), dihydrogen (H 2 ) plasma and dihydrogen sulfide (H 2 S) based on analyses of the morphology of the WS 2 crystals. The WS 2 crystal grain size increases from ∼20 to 200 nm by lowering the nucleation density. This is achieved by lowering the precursor adsorption rate on the starting surface using an inherently less reactive starting surface, by decreasing the H 2 plasma reactivity, and by enhancing the mobility of the adsorbed species at higher deposition temperature. Since silicon dioxide (SiO 2 ) is less reactive than aluminum oxide (Al 2 O 3 ), and diffusion and crystal ripening is enhanced at higher deposition temperature, WS 2 nucleates in an anisotropic island-like growth mode with preferential lateral growth from the WS 2 crystal edges. This work emphasizes that increasing the crystal grain size while controlling the basal plane orientation is possible during ALD at low deposition temperatures, based on insight in the nucleation behavior, which is key to advance the field of ALD of 2D materials. Moreover, this work demonstrates the conformal deposition on three-dimensional (3D) structures, with WS 2 retaining the basal plane orientation along topographic structures. ispartof: CHEMISTRY OF MATERIALS vol:30 issue:21 pages:7648-7663 status: published

The fluoride cycle in the tungsten technology is based on three processes: (1) electrochemical decomposition of HF in KHF2 + HF melt at 80–100 °C with the separate evolution of gaseous fluorine and hydrogen; (2) fluorination of tungsten powder by evolved fluorine at 300–350 °C with the condensation of formed WF 6 in the liquid state at t = 2,5÷3,0 °C; (3) reduction of gaseous WF 6 by evolved hydrogen at t = 580÷600 °C. Hydrogen fluoride is condensed at +1°C after WF 6 reduction and fed for fluorine and hydrogen formation to ensure their circulation in the cycle. The optimization of the used processes suggested technological and equipment solutions for industrial production of large flat and cylindrical semi-products for deformation, as well as tubes, crucibles and other articles of various size from tungsten with a process line capacity of ~4,3 kg/h (>34 tons/year) subject to environmental compliance. In contrast with powder metallurgy methods, the described technology produces non-porous semi-products and ready articles from pure tungsten with more fine-grained structure and virtually unlimited sizes at 2,0–2,5 times lower specific energy consumption per 1 kg of product. For higher production efficiency it is recommended to ensure simultaneous operation of 4 process lines in automatic mode.

In order to simulate tungsten powder fluorination with fluorine and condensation of WF6 produced, computational methods based on the physical and chemical process principles were developed which satisfactorily describe experimental data available. They were used to optimize the equipment size and parameters of two-stage tungsten powder fluorination process with the condensation of liquid WF6 after each stage at 2,5–3,0 °C. The possibility of WF6 production at an output rate of 5,23, 6,53 and 7,83 kg/h in reactors with a diameter of 200, 300 and 360 mm respectively, at a temperature of 300–350 °C without forced cooling of the most heat-stressed first fluorinator was demonstrated. Besides, the total fluorine utilization over 99,99 % was achieved with the amount of hazardous gases escaping the process (F2, WF6) below their maximum permissible concentrations even in the ventilation gas volume. Some recommendations were given on the organization of tungsten powder fluorination flow process.

A method of calculating and optimizing a counterflow symmetric cascade with an arbitrary number of feed streams and additional product streams was developed. A computational experiment on the separation of a tungsten hexafluoride mixture was performed. It was shown that additional product streams are expedient for obtaining a high concentration of intermediate-mass components. The most effective cascade is a combined R cascade, whose depletion and enrichment parts are reckoned according to different pairs of key components.

Objectives: The aim of this study is to identify physicochemical properties such as chemical composition, size, shape and crystal structure of powder byproducts generated from a metallization process and its 1st scrubber in the semiconductor industry. Methods: Powder samples were collected from inner chambers during maintenance of the W-plug process equipment (using tungsten hexafluoride as a precursor material) and its 1st scrubber. The chemical composition, size and shape of the powder particles were determined by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive spectroscope (EDS). The crystal structure of the powders was analyzed by X-ray diffraction (XRD). Results: From the SEM-EDS and TEM-EDS analyses, O and W were mainly detected, which indicates the powder byproducts are tungsten trioxide (WO3), whereas Al, F and Ti were detected as low peaks. The powder particles were spherical and nearly spherical, and the particle size collected from the process equipment and its 1st scrubber showed 10-20 nm (agglomerates: 55-90 nm) and 16-20 nm (agglomerates: 80-120 nm) as primary particles, respectively. The XRD patterns of the yellow powder byproducts exhibit five peaks at 23.8ﾟ, 33.9ﾟ, 41.74ﾟ, 48.86ﾟ and 54.78ﾟ, which correspond to the (200), (220), (222), (400), and (420) planes of cubic WO3. Conclusions: We elucidated the physicochemical characteristics of the powder byproducts collected from W-plug process equipment and its 1st scrubber. This study should provide useful information for the development of alternative strategies to improve the working environment and workers' health.

The reduction of WF6 with hydrogen on a heated surface under atmospheric pressure, temperatures of 500–600°C, and a stoichiometric ratio of components with the subsequent additional reduction of tungsten hexafluoride at t = 800°C and condensation of formed HF is described. The method of calculation of the completeness (α) of reduction of WF6 and productivity (M) of deposition of tungsten depending on the temperature, gas flow rate, and sizes of the reaction surface is developed based on the physicochemical mechanism of the process. The possibility of attaining M = 5.1 kg/h and α = 80% when fabricating crucibles 300 mm in diameter and 500 mm in height is shown. The additional reduction of WF6 provides the summary magnitude α > 99.9%. The almost complete condensation of HF initially at t = +1°C and then at t = −78°C makes it possible to decrease its concentration in exhaust gases below the maximum permissible concentration (MPC).

A comparative investigation into the chemical reactions of a series of fluorinated fullerenes (C60F18, C60F36 and C60F48) with a variety of activated metal surfaces is reported. New ways of generating intense beams of metal fluoride anions are demonstrated: either in reactions of fluorinated fullerene vapours with hot W and Mo metal surfaces in a plasma ion source or by laser desorption/ionisation (LDI) of solid fluorinated fullerenes from various metal substrates (Al, Fe, Cu, Pt, W). In both cases, the resulting metal fluorides and their anions are formed in the highest oxidation state, yielding molybdenum and tungsten hexafluoride anions (plasma ion source), aluminium and iron tetrafluoride anions, and copper trifluoride anions (LDI). No reactions were observed with Pt and W in LDI. The reactivity of the metals towards fluorination correlates with their positions in the metal activity series. Relative yields of bare metal cations are dictated by their ionisation energy. The yield of metal fluoride anions is strongly dependent on the fluorine content of the fluorofullerenes. (C) 2016 Elsevier B.V. All rights reserved.

The experimental coefficients of permeability of fluorine, hydrogen fluoride, uranium hexafluoride, and tungsten hexafluoride through fluoropolymers are presented. It has been shown that vinylidene fluoride polymers have high permeability to hydrogen fluoride. The worst gas permeation characteristics are typical of the materials obtained by molding. The properties of extrusion materials are substantially affected by the molecular weight.

Based on a physicochemical model of the fluorination of tungsten metal fluorine, we derived an equation for calculating the completeness of the use of fluorine depending on the dimensions of the reaction surface, fluorine feed as well as the temperature and the activity of the tungsten surface, which determine the value. The process of WF6 synthesis based on two-fold iteration’ the fluorination of tungsten – WF6 condensation’, which provides the performance of 5.22 kg/hour WF6, the completeness of the use of fluorine >99.99% and the emission of harmful gases within maximum permissible concentration.

Inherent chemical hazards in atomic layer deposition (ALD) processes can be mitigated significantly by careful selection of precursor materials. This work describes the effect of silane (SiH4) exposure on tungsten ALD growth when the silane is heavily diluted (2 at.-%) in argon. A wide ALD temperature window from 200 to ∼300°C is identified, exhibiting a growth rate of between 5 and 6 A per ALD cycle using SiH4 and tungsten hexafluoride (WF6) exposures of ∼6 × 105 and ∼5 × 105 Langmuirs (L), respectively. For deposition at lower temperature (150°C), growth rates of ∼4.5 A per cycle are obtained using a silane exposure of 30 s per cycle, where the partial pressure of silane at the inlet is controlled at 40 mTorr (corresponding to 1.2 × 106 L of silane). Compositional analysis by secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) show less than ∼5 at.-% Si in the W films, with the smallest Si content in films deposited at 300°C. We also describe effects of hot-wall reactor preconditioning on film growth. We conclude that the dilute silane co-reactant offers an alternative to the common disilane, borosilane, or undiluted silane precursors, allowing well-controlled W deposition at 150°C.

Nanocomposite tungsten-aluminum oxide (W:Al2O3) thin films were prepared by atomic layer deposition (ALD) using tungsten hexafluoride (WF6) and disilane (Si2H6) for the W ALD and trimethyl aluminum (TMA) and H2O for the Al2O3 ALD. Quartz crystal microbalance (QCM) measurements performed using various W cycle percentages revealed that the W ALD inhibits the Al2O3 ALD and vice versa. Despite this inhibition, the relationship between W content and W cycle percentage was close to that predicted by theoretical calculations based on the growth per cycle values of binary compounds. Depth profiling XPS showed that the (W:Al2O3) films were uniform in composition and contained Al, O, and metallic W as expected, but also included significant F and C. Cross-sectional TEM revealed the composite film structure to be metallic nanoparticles (∼1 nm) embedded in an amorphous matrix. The resistivity of these composite films could be tuned in the range of 1012–108 Ω cm by adjusting the W cycle percentage between 10% and 30%W. These films have applications in electron multipliers as well as electron and ion optics.

Tungsten carbide / tungsten coating is prepared from tungsten hexafluoride (WF6), hydrogen (H2) and dimethyl ether (DME) mixtures by chemical vapor deposition (CVD) under atmospheric pressure conditions. The cross-sectional structure and the surface morphology of the coating were observed using optical microscope and scanning electron microscopy. It is found that the tungsten layer is columnar and tungsten carbide / tungsten coating is fine grain lamellar structure. The preferential growth of tungsten was proposed to be effect of DME, and the {100} preferred orientation gradually disappeared by XRD. That the pre-deposition of tungsten on the substrate can improve the coverage of the tungsten carbide coating was observed. Finally, the cross section of the micrograph was measured at 28.77 GPa with a nano-indentation.

The combustion synthesis of nanoscale tungsten-oxide particles from tungsten hexafluoride is investigated in a low-pressure hydrogen/oxygen flat flame. The reactor is equipped with molecular-beam sampling of post-flame gases at variable height above burner (HAB). Main species of the flame, intermediate tungsten species, and tungsten-oxide clusters are studied with time-of-flight mass spectrometry (TOF-MS) as a function of HAB. Various WO x (OH) y are identified within the flame front. With increasing HAB, (WO 3 ) n clusters with increasing cluster size appear in the burnt gases at the expense of the concentration of W 1 species. Clusters with n = 3–7 arise at 70 mm HAB, followed by larger clusters at even larger heights. Clusters up to (WO 3 ) 38 were identified. The subsequent formation of nanoparticles is detected with particle mass spectrometry (PMS) and a quartz crystal microbalance (QCM) from 120 mm HAB and the increasing particle size and mass flux have been determined.

A handheld implementation of the ABACC-developed Cristallini method, which captures uranium hexafluoride samples as an inert salt, was organized in FY17 and succeeded in demonstrating the handheld sampler concept with reactive hexafluoride gases. The Cristallini method relies on the use of a hydrated substrate to react the incoming hexafluoride resulting in the formation of a stable uranyl fluoride salt. The Cristallini method has been demonstrated as a facility modification installed near the sampling tap of a gas centrifuge enrichment plant. While very successful in reducing the hazards of uranium hexafluoride sample, the method still takes a considerable amount of time and can only be used in facilities where the apparatus has been installed; this arrangement generally prohibits the sampling of filled cylinders that have already exited the facility and have been deposited in the on-site tank storage yard. The handheld unit under development will allow the use of the Cristallini method at facilities that have not been converted as well as tanks in the storage yard. The handheld system utilizes an active vacuum system, rather than a passive vacuum system in the facility setup, to drive the uranium hexafluoride onto the adsorbing media. The handheld unit will be battery operatedmore » for fully autonomous operation and will include onboard pressure sensing and flushing capability. To date, the system concept of operations was demonstrated with tungsten hexafluoride that showed the active vacuum pump with multiple cartridges of adsorbing media was viable. Concurrently, the hardened prototype system was developed and tested; removable sample cartridges were developed (the only non-COTS component to date); and preparations were made for uranium tests and a domestic field test.« less

A methodology for coupling multiple length scales in chemical vapor deposition processes is presented. A reactor scale model (RSM), used for the description of the macro-scale in the bulk, is coupled with a feature scale model (FSM), used for the description of the topography evolution of the micro-scale features (e.g. trenches or holes) on the wafer. The RSM is implemented with a commercial package and the FSM is implemented by combining a ballistic model for the transport and a profile evolution algorithm based on the level set method. The coupling of the RSM with the FSM is performed through the correction of the boundary condition for the species consumption along the wafer. Essentially, the pre-exponential factor of the Arrhenius expression for the surface reaction(s) is locally corrected along the wafer and this correction allows taking into account the micro-topography on the wafer without including it in the computational domain of the RSM. The coupling methodology implements flow of information in both directions, i.e. from the RSM to the FSM and backwards. Tungsten deposition from tungsten hexafluoride and hydrogen is the case studied. The reactor is axisymmetric and the wafer includes a series of trenches with dimensions at the micro-scale. The effect of the deposition time and the density (number) of trenches on the wafer on (a) the species’ consumption on the wafer and (b) the trench profile evolution is investigated. The loading phenomenon, i.e. the depletion of reactants due to their increased consumption on the micro-topography on the wafer surface is predicted. The importance of the feedback from the micro-scale (to the macro-scale) is demonstrated by comparing trench profiles produced with and without feedback.

The interphase boundary formed in the process of tungsten thin-film deposition on a silicon wafer is investigated. These films are produced via (1) a CVD technique relying on hydrogen reduction of tungsten hexafluoride, (2) the same technique supplemented with plasmochemical action, and (3) magnetron deposition used for comparison purposes. It is shown that a nanometer tungsten silicide W5Si3 layer is formed at the tungsten-silicon interface only under gas-phase deposition. The effect of annealing on the specimen composition and surface resistance is investigated. It is shown that the formation and growth of a silicide WSi2 layer commences at 700°C for CVD films and at above 750°C for films obtained with plasmochemical deposition; this results in a drastic increase in their electrical resistance. Under optimal conditions, tungsten films of 8 × 10 −6 Ω cm resistivity are produced.

The physico-chemical fundamentals (thermodynamics, kinetics) of tungsten carbides crystallization process are presented. Chemically vapor deposited coatings composed of tungsten carbides, metallic tungsten matrix with nanoparticles of tungsten carbides are synthesized from gaseous mixture of tungsten hexafluoride, hydrogen and propane at temperatures ranging from 623 to 923 K and can be used as materials for extreme environments. The physical and mechanical characteristics of these CVD coatings are discussed.

The electron-beam-induced deposition of silicon oxide from tetraethyorthosilicate and tungsten from tungsten hexafluoride is simulated via a Monte Carlo simulation. Pseudo one-dimensional nanopillars are grown using comparable electron-beam parameters and a comparison of the vertical and lateral growth rate and the pillar morphology is correlated to the precursor and deposited material parameters. The primary and secondary electrons (type I) are found to dominate the vertical growth rate and the lateral growth rate is dominated by forward and secondary electrons (type II). The resolution and morphology of the nanopillars are affected by the effective electron interaction volume and the resultant surface coverage of the precursor species in the effective electron interaction region. Finally, the simulated results are compared to previously reported experimental results.

This work demonstrates that two or more elements of negligible solubility (and no known phase diagram) can be co-deposited in fiber form by hyperbaric-pressure laser chemical vapor deposition (HP-LCVD). For the first time, Hg-W alloys were grown as fibers from mixtures of tungsten hexafluoride, mercury vapor, and hydrogen. This new class of materials is termed normally-immiscible materials (NIMs), and includes not only immiscible materials, but also those elemental combinations that have liquid states at exclusive temperatures. This work also demonstrates that a wide variety of other binary and ternary alloys, intermetallics, and mixtures can be grown as fibers, e.g. silicon-tungsten, aluminum-silicon, boron-carbon-silicon, and titanium-carbon-nitride. In addition, pure metallic fibers of aluminum, titanium, and tungsten were deposited, demonstrating that materials of high thermal conductivity can indeed be grown in three-dimensions, provided sufficient vapor pressures are employed. A wide variety of fiber properties and microstructures resulted depending on process conditions; for example, single crystals, fine-grained alloys, and glassy metals could be deposited.

A ternary WN"xC"y system was deposited in a thermal ALD (atomic layer deposition) reactor from ASM at 300^oC in a process sequence using tungsten hexafluoride (WF"6), triethyl borane (TEB) and ammonia (NH"3) as precursors. The WC"x layers were deposited by a novel ALD process at a process temperature of 250^oC. The WN"x layers were deposited at 375^oC using bis(tert-butylimido)-bis-(dimethylamido)tungsten (^tBuN)"2(Me"2N)"2W (imido-amido) and NH"3 as precursors. WN"x grows faster on plasma enhanced chemical vapor deposition (PECVD) oxide than WC"x does on chemical oxide. WN"xC"y grows better on PECVD oxide than on thermal oxide, which is opposite of what is seen for WN"x. In the case of the ternary WN"xC"y system, the scalability towards thinner layers and galvanic corrosion behavior are disadvantages for the incorporation of the layer into Cu interconnects. ALD WC"x based barriers have a low resistivity, but galvanic corrosion in a model slurry solution of 15% peroxide (H"2O"2) is a potential problem. Higher resistivity values are determined for the binary WN"x layers. WN"x shows a constant composition and density throughout the layer.

Electron beam-induced deposition (EBID) provides a simple way to fabricate submicron- or nanometer-scale structures from various elements in a scanning electron microscope (SEM). The growth rate and shape of the deposits are influenced by many factors. We have studied the growth rate and morphology of EBID-deposited nanostructures as a function of the tungsten hexafluoride (WF6) and tetraethylorthosilicate (TEOS) precursor gas pressure and growth time, and we have used Monte Carlo simulations to model the growth of tungsten and silicon oxide to elucidate the mechanisms involved in the EBID growth. The lateral radius of the deposit decreases with increasing pressure because of the enhanced vertical growth rate which limits competing lateral broadening produced by secondary and forward-scattered electrons. The morphology difference between the conical SiO(x) and the cylindrical W nanopillars is related to the difference in interaction volume between the two materials. A key parameter is the residence time of the precursor gas molecules. This is an exponential function of the surface temperature; it changes during nanopillar growth and is a function of the nanopillar material and the beam conditions.

Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30 cm of soft tissue at 80, 100, 120, and 140 kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30 cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems.

The growth of tungsten nitride carbide, WN"xC"y, films obtained by atomic layer deposition (ALD), using tri-ethylboron, tungsten hexafluoride and ammonia precursors is determined by the density and type of substrate reactive sites. During an initial period, referred to as transient regime, the SiC oxidation state and the tri-ethylboron pulse time determine the amount of metal deposited. WN"xC"y growth on SiC is similar to that on PECVD SiO"2 explained by decomposition of the tri-ethylboron precursor, giving rise to a carbon rich WN"xC"y-oxide interface.

Chemical vapor deposition of tungsten silicide into high aspect ratio trenches has been investigated using a commercial 8-inch Applied Materials Centura single wafer deposition tool. For an in-depth study of both step coverage and stoichiometry, a combined chemistry/topography simulator has been developed. Dichlorosilane reduction of tungsten hexafluoride (WF6) has been identified as a suitable chemistry to fill deep trenches with tungsten disilicide, while for WF6 reduction with silane (SiH4) or disilane (Si2H6) fundamental drawbacks have been identified for extreme aspect ratios. In the process range under study, good agreement is observed between the simulated step coverages and those obtained from scanning electron microscope images. The simulations predict a deposition regime in which both good step coverage and a suitable stoichiometry are achieved inside deep trenches.