Effect of tungsten coating on the properties of high-resistivity gold-doped silicon

We have studied the effect of tungsten atoms (tungsten coating) on the properties of gold-doped silicon. The coating considerably increased the resistivity of the silicon and markedly reduced the photoconductivity relaxation time. The silicon doped with gold in the presence of tungsten was found to have an energy level with an ionization energy E = E _c ? (0.23 ± 0.02) eV. In uncoated gold-doped silicon, no energy level with such ionization energy was found. This strongly suggests that the energy level with an ionization energy E = E _c ? (0.23 ± 0.02) eV is due to tungsten centers.     

Effect of a thin diamondlike coating on the emission characteristics of tungsten tips

The effect of an ion-beam deposited carbon coating on a tungsten tip on field emission of electrons has been studied. The analysis of the current-voltage characteristics showed a considerable enhancement of the emission current caused by a decrease in the working function and higher stability of emission from the tip coated with a thin carbon film.     

Crystallization and thermochromism in tungsten oxide films annealed in vacuum

The crystalline phases formed in tungsten oxide (WO_{3 ? x} ) films upon isothermal step annealing in vacuum and air at various temperatures within 500?C750°C have been studied. The films were deposited onto silica glass substrates by reactive dc magnetron sputtering. It is established that the observed thermochromism is related to the presence of an oxygen-deficient WO_{3 ? x} phase belonging to the hexagonal system, which is intensely formed as the annealing temperature increases from 650 to 750°C.     

Experimental evidence of Snoek-like relaxation in annealed metallic glass

The frequency dependence of the internal friction (IF) of annealed Co-based metallic glass (MG) has been measured at elevated temperatures in the frequency range of 10⁻³≤f≤10³ Hz. It has been found that the IF increases with frequency decrease at a constant temperature. To explain this observation, an analytical model of IF due to anelastic relaxation in a symmetrical two-well potential has been proposed. The model shows that the IF rise with decreasing frequency observed in the experiment can be interpreted as a high frequency tail of a Snoek-like relaxation with distributed activation energies in deep relaxation centers of annealed glassy structure.     

Electroless coating of tungsten oxide on the surface of copper powder

Tungsten oxide was successfully deposited on the surface of copper powder and the thickness of coating layer was dependent on deposition time. Because a spontaneous reaction occurred on the interface between copper and tungsten-peroxo electrolyte, there was a maximum thickness that could be obtained, as confirmed from XRD and EDX results. Mesoporous tungsten oxide was also deposited using SDS as a structure directing agent. As-synthesized tungsten oxide was amorphous and, after calcination at 450 °C, crystallized tungsten oxide was produced. Compared to pure tungsten oxide, the tungsten oxide coated copper oxide showed enhanced absorption in the visible region.     

Effect of underlying silicon film on the evolution of microstructure and hardness of the high-temperature annealed carbon film on Si substrate

Effects of an amorphous silicon underlayer on the evolution of microstructure and hardness of an amorphous carbon film annealed at 900 °C for 0.5-1.5 h were investigated. The two-layer carbon/silicon film after annealing resulted in higher sp²/sp³ bonding ratio but lower hardness reduction compared to the single carbon film at the same total film thickness. The improved hardness reduction of the high-temperature annealed carbon film is attributed to the formation of polycrystals of the amorphous silicon together with the residual compressive stress of the two-layer C/Si films.     

处理时间对铝合金微弧氧化陶瓷膜特性的影响

为了研究恒定电流密度下铝合金微弧氧化陶瓷膜的特性随处理时间的变化规律,在工作电流密度设定为25 A/dm2时制备了处理时间分别为1、3、5、10、20、30 min的样品共6块,并采用光学显微镜、显微硬度计、表粗糙度测量仪和SEM等手段对氧化陶瓷膜的形成机理进行了研究.结果表明,陶瓷膜表面呈圆饼状结构,圆饼的中心存在一个放电通道;膜的厚度、表面粗糙度、圆饼和放电通道的直径随处理时间线性增加;陶瓷膜的显微硬度与处理时间密切相关.     

Effect of filament temperature and deposition time on the formation of tungsten silicide with silane

The effect of filament temperature and deposition time on the formation of tungsten silicide upon exposure to the SiH₄ gas in a hot wire chemical vapor deposition process was studied using the techniques of cross-sectional scanning electron microscopy and Auger electron spectroscopy. At a relatively low temperature of 1500 °C, the decomposition of WSi₂ phase and the diffusion of Si towards the silicide/W interface produce a thick W₅Si₃ layer. The diffusional nature leads to a parabolic rate law for silicide growth. An exponential decrease of silicide thickness with temperature between 1600 and 2000 °C illustrates the dominance of Si evaporation at higher temperatures (T ≥ 1600 °C) over the silicide formation.     

Influence of uniaxial compression on the photoconductivity of highly compensated Si〈B, Mn〉

It was observed that the photosensitivity limit and the increase in the photoresponse depend fairly strongly on uniaxial elastic deformation in compensated Si〈B, Mn〉 crystals. Pis’ma Zh. Tekh. Fiz. 24, 23–28 (November 26, 1998)     

The enhancement of relaxation of 0.5PZN-0.5PZT annealed in different atmospheres

The as-sintered Pb(Zn_1/3Nb_2/3)_0.5(Zr_0.47Ti_0.53)_0.5O₃ samples were annealed in oxygen and nitrogen. Both annealed specimens exhibited improved degree of relaxation compared with as-sintered specimens. However, the mechanisms inducing enhancement of relaxation were different in the two kinds of specimens. For the oxygen annealed sample, oxygen vacancies were partially filled, which induced the macro-microdomain transition and resulted in the increase of relaxation degree. Whereas, for the nitrogen annealed specimen, the emergence of pyrochlore phase was inevitable due to the flowing reductive atmosphere, the pyrochlore phase broke the long-range transition invariance of perovskite structure and played a key role in improving the relaxation.     

Atomic relaxation at the kinks of steps on the {112} tungsten surface

Low-temperature field evaporation from 〈111〉 steps on the {112} tungsten surface has been studied using the field ion microscopy techniques. It is established that the atoms at kinks of the steps exhibit anomalous stability with respect to field evaporation. This effect is related to the relaxation of atoms at the kinks. Using geometric analysis of the ion images, the relaxation displacement component normal to the surface was calculated for atoms at the kinks.     

The formation of tungsten carbide in cobalt-base wear-resistant coating alloys

Tungsten carbide-cobalt alloys cannot be produced by melting because of a peritectic reaction in the W-C system; they are produced by sintering. Tungsten carbide-cobalt powders (mixed, agglomerated, sintered) can be plasma sprayed or deposited by other techniques but they cannot be fused afterwards without decomposition of the tungsten monocarbide that provides the best mechanical properties for many applications.Wear-resistant cobalt alloys were developed 60 years ago and are based on cobalt-chromium-tungsten-carbon. During studies of the CoCrWC system with various carbon concentrations and at various temperatures we identified MC, M₂C, M₇C₃, M₂₃C₆, M₆C, M₁₂C and M₂₈C carbides. The solidifying M₆C carbide is unstable over a certain concentration range of chromium and decomposes to form tungsten carbide (WC). On heat treatment the tungsten-containing M₆C forms WC in a cobalt-chromium matrix if the chromium content is less than 5 wt.%. It is therefore possible to produce a sprayed and fused or welded layer of WC-cobalt alloy. The rate of WC formation depends on temperature and time. Time-temperature-decomposition diagrams have been established for four alloys. The structures of the heat-treated alloys are similar to those of sintered tungsten carbide-cobalt alloys.     

合金化时间对热镀锌镀层相结构与结合力的影响

为提高汽车用热镀锌钢板的可焊性,将热镀锌钢板进行合金化退火处理,采用电子显微镜、X射线衍射分析和结合力测试等试验手段,研究了不同时间合金化处理后热镀锌层的表面形貌、化学成分及热镀锌层与基体结合力的变化规律.结果表明:与原始镀锌层为单相Zn以及含有少量Fe相比,经合金化处理后,除了有Zn O和Zn O2相形成之外,同时出现了Zn-Fe金属间化合物;随着合金化处理时间的延长,镀锌层中的Fe含量以及Zn-Fe金属间化合物的Fe含量不断增加;与原始镀锌层和基体的结合力相比,经合金化处理后,镀锌层与基体的结合力增加,并随处理时间的延长,其镀锌层结合力不断提高.     

Photovoltaic properties and photoconductivity in multilayer Ge/Si heterostructures with Ge nanoislands

Interband optical transitions in multilayer heterostructures with SiGe nanoislands were investigated using photocurrent spectroscopy and photo-emf. The n-p heterostructures containing Ge nanoislands in the area of the potential barrier were prepared by molecular-beam epitaxy at the temperature about 500 °C. It was shown that electron transitions from the ground state of the valence band in a nanoislands to the conduction band of Si surrounding made the main contribution into the vertical photo-emf in the range 0.75–1.05 eV, which is below the interband absorption edge of Si. The lateral photoconductivity observed in the range 0.63–0.8 eV at 77 K can be attributed to indirect interband transitions from the ground state of a nanoisland to L-state of the conduction band of a nanoisland. Analysis of Raman scattering spectra revealed that the Ge composition x in a nanoisland is about 0.87, while elastic deformation value amounts to ε _xx  = −0.016. The calculated energies of interband transitions from the ground state of a nanoisland to the conduction band of Si surrounding (0.63 eV) and to L-state of the conduction band of a nanoisland (0.81 eV) fit the experimental data with a rather good accuracy.     

Microstructural characteristics of gas tungsten arc synthesised Fe-Cr-Si-C coating

Abstract

The gas tungsten arc (GTA) method was used to synthesise Fe-Cr-Si-C alloy coatings, and processing effects on the coating were investigated experimentally. Coatings were developed on an AISI type 1040 steel substrate. Four different regions were obtained in the surface coating; and in these regions either a hypoeutectic or a hypereutectic microstructure was found. The hypoeutectic microstructure consisted of primary dendrites of austenite (γ) phase and eutectic M₇C₃ (M=Cr,Fe) carbides. On the other hand, the hypereutectic microstructure consisted of M₇C₃ primary carbides and eutectic. A hypoeutectic or hypereutectic microstructure was determined by the combination of particularly carbon concentration, solidification rate, and extent of substrate melting. The higher hardness of the hypereutectic microstructure is attributed especially to the formation of M₇C₃ primary carbides. The lower hardness of the hypoeutectic microstructure is related to three effective parameters: first, the presence of γ phase in the primary dendrites; second, excessive dilution from the base material; and third, relatively low concentrations of chromium and carbon.     

Effect of pulsed laser irradiation on the photoconductivity of polycrystalline CdTe films

Polycrystalline CdTe films were prepared by molecular-beam deposition onto sapphire and glassceramic substrates at 670 K. The photoelectric behavior of the films (dependence of photoconductivity on incident light intensity and spectral response of photocurrent) was found to depend on grain size. The photoresponse of the fine-grained films in the intrinsic-absorption range and that of the coarse-grained films in the intrinsic- and impurity-absorption ranges increase as a result of above-gap irradiation with 20-ns laser pulses. The dependences of photoconductivity on incident intensity for the coarse-grained films are similar to those for CdTe single crystals. The grain boundaries in fine-grained CdTe films play an important part in the generation and recombination of charge carriers.     

Tungsten chemical vapor deposition using tungsten hexacarbonyl: microstructure of as-deposited and annealed films

Tungsten (W) films were deposited on Si(100) from tungsten hexacarbonyl, [W(CO)₆], by low-pressure chemical vapor deposition (CVD) in an ultra-high vacuum (UHV)-compatible reactor. The chemical purity, resistivity, crystallographic phase, and morphology of the deposited films depend markedly on the substrate temperature. Films deposited at 375°C contain approximately 80 at.% tungsten, 15 at.% carbon and 5 at.% oxygen. These films are polycrystalline β-W with a strong (211) orientation and resistivities of >1000 μΩ cm. Vacuum annealing at 900°C converts the metastable β-W to polycrystalline -W, with a resistivity of approximately 19 μΩ cm. The resultant -W films are porous, with small randomly oriented grains and nanoscale (<100 nm) voids. Films deposited at 540°C are high-purity (>95 at.%) polycrystalline -W, with low resistivities (18–23 μΩ cm) and a tendency towards a (100) orientation. Vacuum annealing at 900°C reduces the resistivity to approximately 10 μΩ cm, and results in a columnar morphology with a very strong (100) orientation.     

Effect of tungsten powder particle shape on the emission properties of the barium tungsten cathode

In this research, porous W matrixes for dispenser Ba-W cathodes were prepared by metal injection molding (MIM) using W powders with different particle shapes as raw materials. Other than investigating the effect of the powder particle shape on the pore characteristics of the porous W matrix, the influence of the powder particle shape on the emission properties of the Ba-W cathode was also investigated. Irregular W powder particles had higher surface roughness and specific surface area than the spherical W particles, resulting in sinuous pore channels and higher pore-specific surface area in the prepared W matrix. The emission current density of the cathode processed from the irregular powder was thus improved as the level of Ba–O dipoles, covered on the emission surface, was increased. This is due to the high pore-specific surface area offering a high contact area between W and impregants in the cathode.