Nickel diffusion in samarium sulfide

The diffusion of nickel atoms in samarium monosulfide (SmS) has been studied for the first time. Using the sequential layer removal technique, it was found that the coefficient of diffusion of the ⁶³Ni radioactive isotope at a temperature of T = 1050°C amounts to D ～ 1.8 × 10^?10 cm²/s in SmS single crystals and to 5.3 × 10^?9 and 1.2 × 10^?10 cm²/s for the fast and slow diffusion components, respectively, in polycrystalline SmS. The process of nickel diffusion in thin polycrystalline SmS films was studied using an X-ray diffraction technique. The coefficient of diffusion at T = 400°C in thin-film samples according to these data is ～10^?13 cm²/s.     

Low temperature interdiffusion in Cu/Ni thin films

Interdiffusion in Cu/Ni thin films was studied by means of Auger electron spectroscopy in conjunction with Ar⁺ ion sputter profiling. The experimental conditions used aimed at simulating those of typical chip-packaging fabrication processes. The Cu/Ni couple (from 10 μm to 60 nm thick) was produced by sequential vapor deposition on fused-silica substrates at 360, 280 and 25 °C in 10^-6 Torr vacuum. Diffusion anneals were performed between 280 and 405 °C for times up to 20 min. Such conditions define grain boundary diffusion in the regimes of B- and C-type kinetics. The data were analyzed according to the Whipple-Suzuoka model. Some deviations from the assumptions of this model, as occurred in the present study, are discussed but cannot fully account for the typical data scatter. The grain boundary diffusion coefficients were determined (for nickel through copper, Q_b = 33.7 kcal mol^-1 (1.46 eV), D_b⁰ = 4.2 × 10^-2 cm²s^-1; for copper through nickel, Q_b = 30.2 kcal mol^-1 (1.3 eV), D_b⁰ = 7.6 × 10^-5 cm²s^-1) allowing calculation of respective permeation distances.     

Ionic conductivity in dehydrated zeolites

The ionic conductivity of pressed pellets of dehydrated synthetic offretite, cancrinite and zeolite A, with various alkali metal ions, was determined by low-frequency impedance spectroscopy. Experiments were carried out in the frequency range 10 Hz–10 MHz at temperatures from 100–600°C. The conduction activation energies range between 55 kJ mol^?1 (Na-zeolite A) and 108 kJ mol^?1 (Li-cancrinite). The best conductivity value obtained was that of Na-zeolite A with 2.9×10^?3Ω^?1cm^?1 at 600°C.     

Volume and dislocation diffusion of iron,chromium and cobalt in CVD ß-SiC

Impurity tracer diffusion of ⁵⁹Fe, ⁵¹Cr and ⁵⁷Co in CVD b-SiC has been studied in the temperature range between 973 and 1873 K. The temperature dependence of the volume diffusion coefficients of iron and chromium can be expressed by linear Arrhenius equations. The preexponential factor and the activation energy are estimated to be 8.7 × 10¹⁵ m² s^-1 and 111 kJ mol^-1 for iron, respectively, and 9.5 × 10¹⁵ m² s^-1 and 81 kJ mol¹ for chromium, respectively. The diffusion coefficients of iron and chromium are much higher than those of the self-diffusion in ß-SiC. Furthermore, the activation energies for the diffusion of iron and chromium are about one-tenth of those for carbon and silicon in b-SiC. Therefore, it seems that an interstitial mechanism is predominant for the diffusion of iron and chromium in b-SiC. On the other hand, the diffusion coefficient of cobalt above 1673 K is higher than that of iron, while at lower temperatures it is much lower than that of iron. The difference in the diffusion coefficients at 1173 K is more than three orders of magnitude. Thus, the temperature dependence of the diffusion coefficients of cobalt shows a strongly curved Arrhenius relation. This suggests that cobalt atoms diffuse by an interstitial mechanism at higher temperatures and by a substitutional mechanism at lower temperatures. From the deeper regions of the penetration profiles of iron, chromium and cobalt the dislocation diffusion coefficients of them have been estimated.     

Flow behaviour and microstructural evolution in cold worked 70∶30 α-brass

Abstract

Deformation behaviour and microstructures at failure were investigated in a mill cold worked 70∶30 α-brass over the test temperature range of 298–973 K and strain rate range of 10^?5–5×10^?3 s^?1. Tensile properties as a function of temperature revealed three distinct regions, with their temperature sensitivity being maximum at intermediate temperatures (553–673 K) and much less towards the lower and higher temperature ranges. Two values of activation energy for high temperature deformation Q were obtained to be 117·5 kJ mol^?1 below 623 K and 196·4 kJ mol^?1 above this critical temperature. In the respective temperature range the values of stress exponent n were 5·6 and 3·8. Based on the values of Q and n, the deformation mechanism was suggested to be dislocation climb creep with a probable contribution from dislocation pipe diffusion on lowering the temperature. Both grain size and cavity size were found to increase with increasing test temperature, suggesting them to be interrelated and act as an alternative steps for accommodating grain boundary sliding. Static grain growth study, over the temperature range of 773 to 1073 K, led to activation energy for grain growth to be 71 kJ mol^?1, with the time exponent of 0·37.     

An ultrasonic study of the diffusion of Ag in CdSe in the temperature range 20°–400 °C

The diffusion of Ag in CdSe has been studied using an ultrasonic technique. The diffusion coefficient was found to be D = 3 × 10^?4 exp (?0.53 eV/kT) cm² s^?1 Diffusion was found to be Fickian in the region up to a depth of 10^?2 cm and one diffusion mechanism was found to dominate. No significant anisotropy was found in diffusion coefficients measured parallel or perpendicular to the c-axis.     

Charge carrier transport in gate-voltage-controlled heteroepitaxial indium arsenide layers

The charge carrier transport coefficients of InAs epilayers, grown on semi-insulating GaAs by chemical vapor phase heteroepitaxy, were investigated by means of gate-voltage-controlled electrical and galvanomagnetic measurements made on metal-oxide-semiconductor structures. The capacitance versus gate voltage dependence of such structures indicates that in the extrinsic temperature region the epilayer surfaces are accumulated for V_g = 0 and flat-band conditions apply for V_g ≈?31 V. It is shown that if the epilayer thickness is corrected for depletion then the epilayer Hall coefficients and conductivities are independent of V_g and have bulk-like values and that the electron mobility has its bulk-like value and is independent of V_g in depletion. In accumulation, the epilayer properties are considered in terms of a composite two-layer model: a bulk-like region of thickness d_b with an average flat-band electron density n_b = 2.5 × 10¹⁵ cm^?3 and mobility μ_b = 7.5 × 10⁴ cm² V^?1 s^?1 and a surface-like region of thickness d_s with a gate-voltage-dependent surface charge density n_sd_s and mobility μ_s where n_sd_s (+30 V) = 2.06 × 10¹² cm^?2 and μ_s(+30 V) = 1.47 × 10⁴ cm² V^?1 s^?1. The monotonic decrease in μ_s with V_g is attributed to scattering of the conduction electrons by localized surface charges which decrease the specularity of the epilayer surfaces.     

Beryllium diffusion and influence on the luminescent and electrical properties of indium phosphide

The diffusion of beryllium in indium phosphide (InP) has been studied. The temperature dependence of the diffusion coefficient can be described by the formula D = 6.3 × 10^?5exp(?1.4/kT) [cm²/s], which yields D = 1.07 × 10^?11 cm²/s at T = 768°C. The results of measurements of the luminescence and electrical properties show that beryllium is a shallow acceptor with an activation energy of 0.03 ± 0.005 meV.     

On the growth of ZnSe on (100) GaAs by atmospheric pressure movpe

High quality, single crystalline, low resistivity ZnSe has been grown on (100) GaAs by atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) using dimethylzinc and hydrogen selenide as reagents. The highest quality material is grown at 553 K with a growth rate of ≈ 14–26 μ h^?1 corresponding to a dimethylzinc flux (2.2–14.8) × 10^?5molmin^?1. The material is characterised by a low donor carrier concentration of 6.0 × 10¹⁴cm^?3, an electron mobility of 415 ± 10 cm²V^?1s^?1 at 298 K and is not highly compensated. The photoluminescence spectrum at 12 K is dominated by a single peak ≈ 2 meV wide at 2.7956 eV. The emission is retained with high intensity at 300 K in a peak corresponding to 2.690 eV and lower energy emission is virtually absent.     

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB₂ superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T _c ) increase with increasing the diffusion-annealing temperature from 650 to 850?°C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850?°C. As for the XRD results, all the samples contain the MgB₂ phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81?×?10^?8 to 4.69?×?10^?7?cm²?s^?1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D?=?3.75?×?10^?3 exp (?1.15?±?0.10?eV/k _B T) and the corresponding activation energy of copper in MgB₂ system is found to be about 1.15?eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.     

Characterization of ohmic contacts to InP

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as ohmic contacts are presented. The layers were heat treated at temperatures up to 550°C and were examined with Auger electron spectroscopy. For contact to n-type InP three thin film systems were investigated: gold, nickel and a composite Ni/Au/Ge layer. Nickel was found to produce ohmic behavior in the Ni/Au/Ge/InP system with a minimum specific contact resistance r_c of 3×10^?5 Ω cm² for a net doping of 3×10¹⁶ cm^?3. For contact to p-type InP a film consisting of Au/Mg was investigated. For heat treatment of the Au/Mg/InP system above 350°C, r_c decreased as the temperature of the heat treatment increased and the surface morphology exhibited increasing signs of alloying at higher temperatures. The smoothest surface was obtained at 446°C for 50 min with r_c≈1×10^?4Ω cm² for a net doping of 6×10¹⁷ cm^?3.     

Rapid H+ conductivity in hydrogen uranyl phosphate-A solid H+ electrolyte

We have found that the layered hydrate HUO₂PO₄. 4H₂O is a rapid proton conductor. The room temperature conductivity of 4 × 10^?3ohm^?1cm^?1 is higher than that of Na⁺ in β alumina. The activation energy is 30± 3 kJ mol^?1. The material is insoluble, and presses into transluscent discs suitable for solid electrolyte applications.     

High strain rate superplasticity of TiNP/2014Al composite

Superplasticity of the TiN_p/2014AI composite prepared by powder metallurgy method was investigated by tensile tests conducted at different temperatures (773, 798, 818 and 838 K) with different strain rates range from 1·7×10° to 1·7×10^?3s^?1. Results show that a maximum elongation of 351% is achieved at 818 K and 3·3·10^?1s^?1. At different deformation temperatures, the curves of m value can be divided into two stages with the variation of strain rate and the critical strain rate is 10^?1 s^?1. Superplastic deformation activation energy in the TiN_p/2014AI composite is 417 kJ mol^?1, which is related to liquid phase formation at triple points of grain boundaries and interfaces between the matrix and the reinforcement. Superplastic deformation mechanism of the TiN_p/2014AI composite is grain boundary sliding accommodate mechanism when the strain rate is lower than 10^?1 s^?1, and transfers to grain boundary sliding accommodation mechanism plus liquid phase helper accommodation mechanism when the strain rate is higher than 10^?1 s^?1     

Sorption-diffusion model of 137Cs uptake by a water body bottom in estimations of water contamination

For a sample including 22 lakes, the ¹³⁷Cs concentrations in water were determined by the sorption-diffusion model. The ¹³⁷Cs levels in waters of lakes of the Kola Peninsula and Karelian Isthmus are satisfactorily described by the suggested model at the distribution coefficient K _d of 4000 L kg^?1 and diffusion coefficient D of 1.0 × 10^?7 cm² s^?1 for 2–4-year exposure. For mid-latitude lakes, the ranges of K _d and D of ¹³⁷Cs were 6000–1200 L kg^?1 and 1.0 × 10^?7–0.2 × 10^?7 cm² s^?1, respectively. The ¹³⁷Cs concentration in water is determined by the major contribution of silts, which are characterized by high K _d of ¹³⁷Cs and by large thickness of sediments on the bottom of lake hollows, to the watter-bottom sorption system. After 2-year exposure of “Chernobyl” ¹³⁷Cs in lakes, its inventory in water relative to the amount that fell out in 1986 did not exceed 14% for deep lakes and 2–3.6% for shallow lakes.     

Evaluation on corrosively dissolved gold induced by alkanethiol monolayer with atomic absorption spectroscopy

We have monitored a gold corrosive dissolution behavior accompanied in n-alkanethiol like n-dodecanethiol assembled process with in situ quartz crystal microbalance (QCM), and then observed it with atomic force microscopy (AFM) which showed an evident image of corrosive defects or holes produced on gold substrate, corresponding to gold dissolution induced by the alkanethiol molecules in the presence of oxygen. For detection of the dissolved gold defects during alkanethiol assembled process, an atomic absorption spectroscopy (AAS) has been carried out in this paper, and the detection limit for the dissolved gold could be evaluated to be 15.4 ng/mL. The amount of dissolved gold from the substrates of gold plates as functions of immersion time, acid media, solvents and thiol concentration has been examined in the oxygen saturated solutions. In comparison with in situ QCM method, the kinetics behavior of the long-term gold corrosion on the gold plates in 1.0 mmol/L of n-dodecanethiol solution determined with AAS method was a slow process, and its corrosion rate on gold dissolution could be evaluated to be about 4.4 × 10^? 5 ng·cm^? 2·s^? 1, corresponding to 1.3 × 10⁸ Au atoms·cm^? 2·s^? 1, that was much smaller than that of initial rate monitored with in situ QCM. Both kinetics equations obtained with QCM and AAS showed a consistent corrosion behavior on gold surfaces.     

Kinetic studies of water uptake and loss in glass-ionomer cements

The water sorption and desorption behaviour of three commercial glass-ionomer cements used in clinical dentistry have been studied in detail. Cured specimens of each material were found to show slight but variable water uptake in high humidity conditions, but steady loss in desiccating ones. This water loss was found to follow Fick’s law for the first 4–5 h. Diffusion coefficients at 22 °C were: Chemflex 1.34 × 10⁻⁶ cm² s⁻¹, Fuji IX 5.87 × 10⁻⁷ cm² s⁻¹, Aquacem 3.08 × 10⁻⁶ cm² s⁻¹. At 7 °C they were: Chemflex 8.90 × 10⁻⁷ cm² s⁻¹, Fuji IX 5.04 × 10⁻⁷ cm² s⁻¹, Aquacem 2.88 × 10⁻⁶ cm² s⁻¹. Activation energies for water loss were determined from the Arrhenius equation and were found to be Chemflex 161.8 J mol⁻¹, Fuji IX 101.3 J mol⁻¹, Aquacem 47.1 J mol⁻¹. Such low values show that water transport requires less energy in these cements than in resin-modified glass-ionomers. Fick’s law plots were found not to pass through the origin. This implies that, in each case, there is a small water loss that does not involve diffusion. This was concluded to be water at the surface of the specimens, and was termed “superficial water”. As such, it represents a fraction of the previously identified unbound (loose) water. Superficial water levels were: Chemflex 0.56%, Fuji IX 0.23%, Aquacem 0.87%. Equilibrium mass loss values were shown to be unaffected by temperature, and allowed ratios of bound:unbound water to be determined for all three cements. These showed wide variation, ranging from 1:5.26 for Chemflex to 1:1.25 for Fuji IX.     

Thermal behaviour of gas atomised Al–20Mg–2Zr alloy powder

A novel ternary alloy with the composition of Al–20Mg–2Zr (wt-%) was prepared by close coupled gas atomisation. The thermal oxidation behaviour of the powder was examined by thermogravimetry–differential thermal analysis. The results showed that the oxidation proceeded in single step, and the violent exothermic reaction occurred after 900°C was almost complete. The activation energy of the oxidation was ～250?kJ?mol^??1, and the frequency factor was ～1.47?×?10¹¹?s^??1 and 3.36?×?10¹¹?s^??1 using the Kissinger and Ozawa method respectively. The special feature of the pulsed oxidation was explained by the melt dispersion oxidation mechanism. The excellent thermal reactivity exhibited by the Al–20Mg–2Zr powder suggested that this novel alloy could become one of the most promising materials in energetic applications.     

Spin exchange rate constant for collisions of metastable helium atoms with rubidium atoms

The spin exchange rate constant C _se in the He(2³S₁)-Rb(5²S_1/2) system has been measured for the first time in experiments on the optical orientation of metastable helium atoms in the presence of rubidium atoms. In the temperature interval T = 293–348 K, this value is C _se = (1.8 ± 0.4) × 10^?9 cm³ s^?1. The chemiionization rate constant, which has been simultaneously measured in collisions of these particles, is C _ci = (3.1 ± 0.6) × 10^?9 cm³ s^?1.     

Investigation of the transport properties of InSb single-crystal films obtained by directional crystallization

Both n-type and p-type InSb films (with a wide range of carrier concentration) were obtained by the directional crystallization method from the melt on large areas of mica, quartz and sapphire substrates. The p-type films were doped with germanium. It is shown that, depending on the crystallization conditions, one can obtain films of different structure: dendritic films, films containing macrodefects and homogeneous single-crystal films. The optimal growth conditions of single-crystal films having transport properties close to those of bulk material are given. The investigation of some transport properties in single-crystal p-type InSb films was carried out in the temperature range 77–600 K.A hole mobility in the range from 180 cm² V^-1 s^-1 to 5×10³ cm² V^-1 s^-1 in films with a concentration p=1.2×10¹⁶?5×10¹⁸cm^-3 of uncompensated acceptors was observed.An investigation of the concentration and temperature dependence of the hole mobility was carried out. Experimental results are in good agreement with the theory if a combined impurity, acoustic and optical mode scattering is taken into account.The phonon drag effect in p-type InSb films was observed. The temperature dependence of the thermoelectric power shows fair agreement with Herring's theory.