The equivalent channel model for permeability and resistivity in fluid-saturated rock—A re-appraisal

It is affirmed that a consistent development of the equivalent channel model for both fluid permeation and electrical conduction in saturated porous media leads to the expression CR²/F where R is the hydralic radius, F the formation resistivity factor or tortuosity/porosity ratio and C a numerical factor generally around 0.3 to 0.4. This expression is approximately supported by observations reported on granular media and fairly porous rocks. Confirmation of its applicability to low porosity, microcracked rock is still lacking but it would appear to be consistent with measurements on granite in that it indicates that the hydraulic radius (represented by half the mean crack opening width) decreases as the confining pressure is increased. In any application it is important in estimating R and F to take only the connected porosity into account.     

Magneto-mechanical properties evolution of Fe–C alloy during precipitation process

Evolution of magneto-mechanical properties of 160 ppm Fe–C alloy due to carbides precipitation during isothermal annealing at 473 K (up to t=50×10³ s) was studied by means of classical Barkhausen noise (HBN) and mechanical Barkhausen noise (MBN) effects. The MBN was measured for the torsion mode of load with a torque motor. Also the B(H) hysteresis loop and the coercive field H_c were evaluated using a low-frequency magnetisation set. Magnetic hysteresis losses ΔW₁ were compared with the integral ΔW₂ of HBN intensity over one period of magnetisation and the integral ΔW₃ of MBN intensity over one period of the mechanical load. The internal stress distribution function and the resulting mean level of internal stress parameter σ_i were evaluated from the MBN ‘first load’ data. It was revealed that a correlated increase of ΔW₁ and ΔW₂ parameters exists. However, the relative increase of ΔW₃ is much lower than the relative increase of ΔW₁. The relationship between H_c and σ_i was found to be parabolic. This dependence explained by Néel’s model of the impact of the residual stress level on H_c. The presence of precipitates of type was confirmed by scanning electron microscopy.     

Selective tungsten CVD on submicron contact hole

This work investigates the deposition properties of selective chemically vapor-deposited tungsten for filling the deep sub-half micron contact holes using the process of silane reduction of tungsten hexafluoride. Low-resistivity tungsten with excellent selectivity and conformal coverage can be obtained with a SiH₄/WF₆ flow rate ratios less than 0.6 at deposition temperatures between 280 to 350 °C. Junction leakage and contact resistance of the AlSiCu/W/n⁺P and AlSiCu/W/p ⁺ n diodes as well as the electromigration properties of the AlSiCu/W/n⁺ p structure were investigated.     

Computer simulation of martensitic textures

We consider a Ginzburg-Landau model free energy F(ε, e₁, e₂) for a (2D) martensitic transition, that provides a unified understanding of varied twin/tweed textures. Here F is a triple well potential in the rectangular strain (ε) order parameter and quadratic e₁², e₂² in the compressional and shear strains, respectively. Random compositional fluctuations η(r) (e.g. in an alloy) are gradient-coupled to ε, ˜ − ∑_rε(r)[(Δ_x² − Δ_y²)η(r)] in a “local-stress” model. We find that the compatibility condition (linking tensor components ε(r) and e₁(r), e₂(r)), together with local variations such as interfaces or η(r) fluctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective ε-ε interactions. We have carried out extensive relaxational computer simulations using the time-dependent Ginzburg-Landau (TDGL) equation that supports our analytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and Fe_xPd_{1 − x} alloys can be explained on the basis of our analysis and simulations.     

Some physical properties of ZnO sputtered films

The secondary electron emission (SEE) yield δ of ZnO films was investigated. The films were deposited in an r.f. sputtering system using the r.f. power W, the argon pressure p, the O₂ partial pressure p_O2 and the substrate temperature T_s as parameters. Complementary measurements of the electrical resistivity and the optical absorption were performed. The ratio x of oxygen to zinc is an essential factor which determines the values of δ, and for the ZnO films.

Auger analyses showed that excess (overstoichiometric, x =1) oxygen is present in ZnO films obtained at room temperature. For x =1 the values of , the maximum SEE yield δ_m and the energy band gap E_g (determined from ) were found to be higher than those for stoichiometric ZnO (obtained at T_s200 °C). The highest values of (10⁴ Ω m), δ_m (4.4) and E_g (3.44 eV) were obtained for films with x = 1.7.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Role of passivating oxide film in the corrosive wear of Al-7%Si alloy

The present work examines how passivating oxide film affects the corrosive wear rate of Al-7%Si alloy in H₂SO₄ solution at room temperature. As the applied potential (relative to a saturated calomel electrode (SCE)) increases to 1.08 V_SCE on an Al-7%Si alloy specimen, the corrosive wear rate increases and then decreases for polarization to higher anodic potentials. The corrosive wear rate W_cw consists of three factors, namely pure mechanical wear loss W_mech, weight loss W_diss caused by the corrosion reaction, and an acceleratory-deceleratory contribution W_acc due to the presence of passivating oxide film. The acceleratory and deceleratory contributions W_acc arising from compositional change of the passivating oxide film indicate the microcutting and microploughing mechanisms respectively of abrasive wear. The increased W_acc by application of 1.08 V_SCE is discussed from the viewpoints of hydration and severe abrading wear action of the passivating oxide film on the Al-7%Si alloy specimen.     

Space-charge-limited conductivity in evaporated cadmium selenide thin films

We have studied the basic d.c. electrical properties of evaporated CdSe films in the context of the development of inexpensive solar cells. Earlier measurements have shown significant variations, which depend on the preparation and previous treatment of the films. In the present work Al---CdSe---Al sandwich structures were studied, with the CdSe thickness in the range 0.1–1.0 (μm. D.c. capacitance varied inversely with film thickness, yielding a permittivity of 7.82 × 10⁻¹¹ F m⁻¹ (relative permittivity 8.83). Current density was proportional to applied voltage at low voltage levels, but followed a power law at higher voltages with exponent typically 2.5; the transitional voltage was directly proportional to the square of the film thickness. The results were interpreted as ohmic conduction at low voltages and space-charge-limited conductivity (SCLC) dominated by an exponential trap distribution, at higher voltage levels. Measurements of current density as a function of inverse temperature for different applied voltages in the SCLC region enabled the derivation of typical mobilities in the range of ( 7.65–10.15) × 10⁻⁵ m² V⁻¹ s⁻¹ using the results of our existing theory. This value of mobility and the derived trapping parameters were in general agreement with some earlier measurements.     

Element Availability Importance in Generalized k-out-of-r-from-n Systems

An algorithm for evaluating the overall system availability and the availability importance of elements in a generalized consecutive k-out-of-r-from-n:F system is presented. This system consists of n linearly ordered nonidentical elements with different reliability characteristics and performance rates. Each element can have two states: (i) complete failure with a performance rate of zero; and (ii) perfect functioning with a nominal performance rate. The system fails if the sum of the performance rates of any r consecutive elements is lower than a demand W. The suggested algorithm, based on an extended universal moment generating function, is convenient for numerical implementation. Analytical and numerical examples of evaluating availability importance indices are presented.     

用电化学噪声技术研究Q235钢在含氯盐模拟混凝土孔隙液中的腐蚀行为

采用电化学噪声技术(EN)和电化学阻抗谱(EIS)研究了Q235钢在0.5 mol/L NaCl的饱和Ca(OH)₂溶液(SCP)中的腐蚀过程,并对噪声数据进行时域分析与频域分析,对阻抗谱数据进行等效电路分析。采用SEM结合EDS和XRD研究了Q235钢的表面形貌和结构组成。结果表明,Q235钢在SCP溶液中的腐蚀过程可分为钝化膜的形成与破裂阶段(Ⅰ)、亚稳态点蚀阶段(Ⅱ)和Ca²⁺沉积和腐蚀产物形成阶段(Ⅲ)。在(Ⅰ)阶段,电流噪声的波动幅值较小,电流噪声标准偏差S_I、白噪声水平W_I较小、噪声电阻R_n较大;在(Ⅱ)阶段,电流噪声波动幅值较大,S_I、W_I呈现阶跃式增长,R_n显著降低;在(Ⅲ)阶段,电流噪声波动幅值增大到200 nA,S_I、W_I、R_n平稳波动。Q235钢在SCP溶液中腐蚀10 d后在其表面出现Fe₂O₃和弥散分布的CaCO₃晶体,此时阻抗谱中出现类Warburg阻抗,腐蚀反应受电荷转移和O₂扩散的联合控制。     

Exploring the fracture toughness KIE and KIC of a medium-Strength steel plate using the surface-flaw test

The fracture toughness of a 30 CrMnSiA steel plate of three thicknesses (10,8 and 5 mm) and three widths (110,80 and 56 mm) has been investigated by using surface-flaw method under room temperature. It is not easy to compute the value of K_IE by the maximum applied load. But the values of K_IE and K_IC could be obtained easily, if the computation of the conditional applied load P₁₀ and P₅ based on the relative effective extension Δa/a₀ = 10% and 5% were adopted, together with the conditions of P_max/P₁₀ 1.2 and P_max/P₅ 1.3. The K_R — Δ_a curve, i.e. the resistance-curve described by the parameter K, has been plotted. The values of K_IC and K_IE are then the resistances corresponding to the real extensions of flaws of Δ/a₀ = 2 and 7%, respectively. These values so obtained are in good agreement with the computed values of K_IC and K_IE by using the conditional applied loads. The values of K_IC and K_IE so obtained are also in agreement with the value of K_IC converted from the J-integral and the effective value of K_IE computed by the maximum applied load, respectively.

An approximate relation between K_IC and K_IE has been found to be: K_IC = (0.85˜0.95)K_IE.

The requirements for the dimensions of specimens are: Thickness of plate: B 1.0(K_IC/σ_0.2)² or 1.25(K_ICσ_0.2)²]; Width of plate: 8 W/B 10, 4 W/2c 5; Effective length: l 2W.     

The microscopic theory of diffusion-controlled defect aggregation

The kinetics of diffusion-controlled aggregation of primary Frenkel defects (F and H centers) in irradiated CaF₂ crystals is theoretically studied. Microscopic theory is based on the discrete-lattice formalism for the single defect densities (concentrations) and the coupled joint densities of similar and dissimilar defects treated in terms of the Kirkwood superposition approximation. Conditions and dynamics of the efficient F center aggregation during crystal heating after irradiation are analyzed.     

Structural, chemical, and electrical characterisation of reactively sputtered WSx thin films

WS_x films were sputter-deposited on Si, SiO₂/Si, and glass substrates from a WS₂ target in an Ar/H₂S atmosphere. Their structure, morphology, chemical composition, and electrical properties were investigated as a function of deposition parameters such as working pressure and H₂S fraction. Films could be grown in the composition range WS_0.3−WS_3.5. Crystallisation was achieved at substrate temperatures T_s > 70 °C and compositions 0.7 ≤ x ≤ 1.95. While the first 5–50 nm near the interface exhibited a basal orientation (c), further growth resulted in the formation of edge-oriented platelets (c) giving rise to a porous, lamellar microstructure. The crystalline structure was mainly turbostratic, while some degree of ordered stacking was present in samples grown at high substrate temperature (600 °C). Resistivity measurements showed a semiconductor-type temperature dependence characterised by activation energies up to 95 meV. Sheet resistance was found to be nearly independent of film thickness, suggesting that the main carrier transport takes place in an interfacial layer of about 20 nm in thickness.     

SiC nanocrystals embedded in oligoetheracrylate photopolymer matrices; new promising nonlinear optical materials

Photoinduced optical phenomena in SiC nanocrystallites embedded within the photo-polymer oligoetheracrylate matrices have been studied using experimental nonlinear optics, particularly photoinduced optical second harmonic generation (SHG). The YAG-Nd-laser (λ=1.06 μm; W=30 MW; pulse duration within the 30–50 ps) was used as a source of pumping light and the nitrogen laser (λ=337 nm) has been applied as a source of the photoinducing light. With increasing intensity of the photoinducing beam, the SHG (λ=0.53 μm) signal increased and achieved a maximum (χ₂₂₂=10.1 ± 0.13 pm/V) at a photon flux of about 1.61 GW/cm². With decreasing temperature, the SHG signal strongly increases within the temperature range 25–30 K. Time-dependent probe–pump measurements indicate an existence of the SHG maximum for a pump–probe time delay of about 20 ps. The SiC hexagonal structural components play a key role in the observed photoinduced nonlinear optical effects. Large values of the nonlinear optical constants as well the good technological parameters open a possibility to enhance the nonlinear optical susceptibilities.     

Effect of N2O/SiH4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH₄---N₂O. The effect of a gas-phase reaction on the SiO₂ film properties and Si/SiO₂ interface was investigated. As the partial pressure ratio was increased above N₂O/SiH₄ = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N₂O/SiH₄ <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si---OH and Si---H) but when N₂O/SiH₄ >4, the incorporation of Si---OH bond became significant and Si¹⁺, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C---V and I---V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO₂ interface.     

磷酸银纳米结构的调控及其光催化性能研究

基于十二烷基硫酸钠(SDS)、环己烷、异戊醇和水溶液构建的反相微乳液体系, 以硝酸银、磷酸二氢钾为原料, 通过改变水与表面活性剂物质的量比值(W)调控制备出棒状、纺锤状及四面体状磷酸银(Ag₃PO₄)纳米材料。利用XRD、SEM、TEM和UV-Vis-DRS光谱对样品结构、形貌以及可见光响应特性进行了表征, 探讨了不同形貌Ag₃PO₄的形成机理, 并以次甲基蓝(MB)降解效果评价了样品光催化性能。实验结果表明: 制备的系列纳米Ag₃PO₄均为体心立方结构晶体, 其形貌受W值影响明显; Ag₃PO₄形貌的不同主要由于SDS量的变化改变了含有产物水核的直径与界面膜强度。此外, 制备的样品均表现出好的可见光催化降解MB性能, 其中, 具有完整四面体形貌的Ag₃PO₄光催化性能最佳, 这与其能够裸露出多的{111}晶面有关。     

CO在U2N3+xOy薄膜表面反应特性研究

采用磁控溅射沉积方法在Si基底表面制备U₂N_3+xO_y薄膜, 采用X光电子能谱(XPS)分析技术观测CO气氛环境下U₂N_3+xO_y薄膜表面腐蚀行为, 以期获得U₂N_3+xO_y薄膜在CO环境下的表面腐蚀机理。结果表明: 超高真空条件下, CO在U₂N_3+xO_y薄膜表面表现为氧化特性; CO在薄膜表面吸附解离生成的C以无定形碳形式聚集在薄膜表面, 深度剖析过程中并未观察到C向U₂N_3+xO_y薄膜内部扩散; 而解离生成的氧在薄膜内扩散并发生氧化反应, 生成高价氧化物或铀氮氧化物和氮。氧化反应生成的氮向薄膜内部扩散, 并在次表面反应生成富氮中间产物。随着CO暴露反应进程的推进, 富氮层逐渐向薄膜内部迁移, 这是导致U4f谱卫星峰变化的主要原因。     

On the ratio (Φ) of the J-integral to the total work done per unit uncracked area

The ratio (Φ) of the J-integral to the total work done per unit uncracked area is shown to be dependent upon Poisson's ratio (v) in both plane stress and plain strain conditions. An expression for Φ in three-point-bending of linear elastic materials is derived analytically as a function of a/W (initial crack size/width), S/W (span/width) and v. The variation of Φ on the Poisson's ratio and a/W is illustrated in both graphical and tabulated fonns for S/W = 4. Error margins are discussed when Φ is taken as 2.00 universally for all materials exhibiting linear elastic behavior when a/W exceeds 0.5. The Φ value is experimentally detennined for several a/W ratios using a polymeric material. This experimental result is compared with an analytic prediction shown in the present study. The prediction is in good agreement with the experimental result.     

Physics and diagnostics of laser ablation plume propagation for high-Tc superconductor film growth

The formation, composition and propagation of laser-produced plasmas used for pulsed laser deposition (PLD) of Y₁Ba₂Cu₃O_7−x have been studied under film growth conditions. Four complementary spatially and temporally resolved in situ diagnostic techniques are applied to characterize the expansion of the laser plume into both vacuum and ambient gases: optical emission and absorption spectroscopy, fast ion probe measurements, and fast photography with a gated, image-intensified charge-coupled detector-array (ICCD) camera system. Transient optical absorption spectroscopy reveals large densities of ground state atoms, ions, and molecules in the plume as well as a slower component to the plume transport than is indicated by the plasma fluorescence and ion current.

Ablation into background gases results in scattering and attenuation of the laser plume. The exponential attenuation of the positive ion flux transmitted through 50–300 mTorr background oxygen is measured and used to define an overall ion-oxygen reaction cross-section σ_i−O2 = 2.3 × 10⁻¹⁶ cm² under the described film growth conditions.

The slowing of the laser plasma and formation of shock structures due to collisions with the ambient gas are described using ion probe measurements and ICCD photographic comparisons of expansion into vacuum and background oxygen. At the pressures used for PLD, distance-time R−t plots derived from the photographs and ion probe waveforms indicate that the higher pressure plume initially expands through the ambient gas in accordance with a drag model (where R = x_f[1 − exp( − βt)]), experiencing little slowing until a visible shock structure forms. Following a transition period, in which the plume appears to have two components, a single-component shock structure propagates in better agreement with a shock, or blast wave (R = ξ₀(E/₀)^1/5t^2/5) model.     

Exclusion zone model of islands spatial distribution in molecular beam epitaxy

A simple model of islands spatial distribution based on the statistical nucleation model combined with a forbidden for nucleation zone is proposed. Islands nucleate at random points of uncovered substrate with a constant rate and then grow in a hemisphere at a constant velocity. Around each growing island there exists an exclusion zone of some width L within which nucleation is forbidden, while outside this zone islands continue to germinate in a usual spatially random fashion. By this model formulas for the probability that an arbitrarily chosen surface region at any given time moment t will be either empty or contain just one island, W₀(t) and W₁(t), respectively, are derived. Calculations with this formula shows that a simple introduction of the forbidden zone leads to some ordering degree in a spatial distribution of islands, similar to that observed in experiments, and provides a good quantitative coincidence with experiment at reasonable values of the model parameter L.