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The characteristics of shear bands in cold-rolled Ta-2.5W alloy are systematically investigated at different mechanical reduction levels. With increasing strain, the shear bands can appear as in-grain shear bands, trans-granular shear bands and wavy bands. At low strain the crystallographic planar in-grain shear bands are aligned close to the highly stressed slip planes at low strain. As strain increases, the shear bands rotate around the or direction to smaller inclination angles with respect to the rolling direction (RD). Meanwhile, new groups of shear bands are developed. Two groups of in-grain shear bands with a specific fishbone structure appear in the orientations with larger Taylor factor at medium strain. The trans-granular shear bands are formed when the adjacent grains get the continuity of slip planes. Therefore, the frequency of trans-granular shear bands increases with the enhancing of local texture. The wavy bands appear to be a result of sequential necking in the harder γ-fiber and a cooperative flow in the softer α-fiber. Meanwhile, the formation model of the wavy bands is also proposed based on the laminar composites.

Elongated lamellar bands parallel to rolling plane are usually formed in γ-fiber of Ta W alloys at high strains. However, in this study, a type of lamellar bands oriented with α-fiber is formed in Ta 10 W alloy cold-rolled to 5%. Meanwhile, island equiaxed grains with special orientations can be seen in the lamellar bands. Furthermore, the lamellar bands are not homogenously distributed in the whole samples and concentrated in some elongated-grain bands. Although the lamellar bands are composed of extending planar dislocation boundaries with one or two dislocation cells across, they cannot result from incremental rotation of microbands or microshear bands, since no shear bands appear in these lamellar bands at such low strain. Therefore, the lamellar bands can be initiated by the retained elongated lamellar boundaries after annealing. They show a persistent microstructural feature as the ratio of reduction increases. As the hardness and dislocation density of the persistent lamellar bands is quite different from that of other deformed microstructures, these bands are bad for plastic deformation process. Meanwhile, protrusions at high-angle lamellar boundaries migrating to the recovered lamellar bands are observed during annealing because of the inhomogeneous dislocation microstructure. The lamellar bands can be fully eliminated when the annealing temperature reaches 1500 °C.

Glasses and vitroceramics in the xMoO 3 ·(100 − x)[4PbO 2 ·Pb] system with x = 5-50 mol% MoO 3 were prepared by melt quenching method. The influence of MoO 3 content on optical properties and structure of the 4PbO 2 ·Pb host network was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, photofluorescence and X-ray photoelectron (XPS) spectroscopies. The X-ray patterns show the presence of a small amount of Pb 2 MoO 5 crystalline phase in the sample with x = 40 mol% MoO 3 . By increasing of MoO 3 content up to 50 mol% MoO 3 , Pb 2 MoO 5 and tetragonal PbO crystalline phases were detected. Raman data show the bending modes of the O Pb O linkages which allow the intercalation of [PbO 4 ] structural units, isolated [MoO 4 ] and deformed [MoO 6 ] structural units as basic structural units formed by lead and molybdenum atoms. The photofluorescence spectroscopy data shows the transitions of Mo + 5 and Pb 2 + ions. According to the XPS data, the vitroceramic network contains mainly [MoO 4 ] tetrahedral units and small amounts of [MoO 6 ] octahedral units.

The effect of tungsten content on deformation texture and microstructure of Ta-W alloy is studied. It is found that the increase of tungsten content results in the strengthening of α-fiber and the weakening of γ-fiber in Ta-W alloys. The volume fraction of γ-fiber developed in Ta-10W alloy is lower than that in Ta-2.5W alloys. Meanwhile, a more significant through-thickness texture gradient is formed in Ta-10W alloy. The addition of tungsten has an important effect on the ability cross-slip of dislocations. Therefore, more dislocation loops and activated slip systems can be seen in Ta-2.5W alloy. The size of the dislocation cells in Ta-2.5W alloy is larger than that in Ta-10W alloy. As shear bands tends to appear in γ-fiber, the density of shear bands in the Ta-2.5W alloy is much higher than that of Ta-10W alloy at the same reduction strain. Meanwhile, the wavelength of the wavy shear bands in Ta-10W alloy is smaller than that in Ta-2.5W alloy. In Ta-10W alloy, new grains with Goss orientation can be seen in periodic shear bands developed in {111} orientations, which is different from that in Ta-2.5W alloy.

The influence of DC current on the resistivity and phase transition of polycrystalline La 0.7 Ca 0.3 MnO 3 has been investigated. The specific heat measurement found that charge carriers and ferromagnetic spin-wave contributions were changed after applied DC current. Applying high electric fields leads to the formation of ferromagnetic regions. The resistivity drops abruptly once the percolating current path is established. As current through the sample disappears, the larger ferromagnetic (FM) clusters, however, remain and are frozen in giving a measurable contribution to the specific heat of the system. The larger clusters should give rise to the value of spin-wave stiffness constant ( D ), as it is expected to increase the strength of the ferromagnetic coupling. The metallic ferromagnetic regions would make the charge carrier delocalization and attribute to specific heat linear term γ .

A new high-temperature thermal sensor based on large-grain polysilicon film formed by metal-induced lateral crystallization (MILC) is proposed. The sensor demonstrates a positive temperature coefficient (PTC) characteristic from 130 °C to high temperatures above 600 °C. Its fabrication process is more cost-effective than its silicon on insulator (SOI) counterpart, and its performance is better than the sensor based on small-grain polysilicon formed by solid-phase crystallization (SPC). Therefore, the proposed sensor is more suitable to be integrated into single-chip CMOS-MEMS gas-sensor system for monitoring the high temperature of sensing membranes.

La0.67Ca0.33MnO3 (LCMO)/YBa2Cu3Oy (YBCO)/Ni trilayers were fabricated with varying thickness of the mid-superconducting YBCO layer. Two different deposition systems were used to avoid oxidation of the magnetic metal Ni and contamination of the deposition systems. Transport properties show that the temperature dependence of resistance goes from a metallic-to-metal-insulator transition (manganite-like behavior) to a superconducting behavior (M-M-S) with increase of the thickness of the YBCO layer. The magnetoresistance (MR) ratio is very small in comparison with LCMO/YBCO bilayers at low temperature. Such phenomenon may depend on the charge transfer and the magnetic spin interaction between the bottom and cap magnetic layers. (c) 2005 Elsevier B.V. All rights reserved.

A thermal sensor built from a silicon resistor with a simple rectangular layout structure on thin-film (0.1 μm) silicon-on-insulator (SOI) substrate is studied and compared with those on thick-film (10 μm) SOI and bulk (450 μm) Si. Besides supporting the theory of minority-carrier exclusion effect through one-dimensional highly confined carrier transport in the ultra-thin rectangular silicon film, the thin-film SOI device demonstrates the effect of silicon-film thickness on the maximum operating temperature ( T max ) of the sensor: thinner Si film results in higher T max due to higher current density and hence stronger exclusion effect. Measurements and simulations both show that the SOI structure can indeed have the silicon-film thickness as an additional degree of freedom for increasing T max . More importantly, the thin-film SOI thermal resistor can achieve a T max beyond 400 °C even under a very low operating current of 0.1 μA, which is about 1000 times smaller than that of the thick-film SOI counterpart with the same T max . In conclusion, silicon resistor on SOI is a promising low-cost thermal sensor for a broad scope of low-power high-temperature applications.

We present the aggregation of silver perchlorate molecules in Langmuir-Blodgett films, which are generated from the reaction of silver arachidate multilayers with perchloric acid gas. Salt-acid conversion and structural variation of the films are investigated. The morphology of silver perchlorate clusters is visualized using atomic force microscopy. Plate-like clusters with diameters of several nanometres are presumed to result from the assembly of neighbouring smaller particles.

A high-gain and broadband printed antenna together with its feed network is developed, which consists of seven hexagonal sub-arrays as cells, each one is a hexagonal compound air-fed array (CAFA), arranged in a beehive-like shape. After choosing an optimal feeding-voltage ratio of the central cell to the circumjacent cells as 0.42, the corresponding feed network is carefully designed. The measured results of a fabricated prototype are of common bandwidth (for VSWR ⩽ 2.0÷1 & gain-drop ⩽ −3 dB & SLL ⩽ −15 dB) 8.28 % and maximal gain 22.51 dBi, while the simulation results are 9.63 % and 22.87 dBi.

Based on the minority-carrier exclusion theory, an analytical model is developed to explain the operating principle of thermal sensors fabricated on silicon-on-insulator in terms of the carrier-concentration distribution and the temperature dependence of the sensor resistance. The effects of temperature and carrier concentrations on carrier mobilities are included in the model. A two-region model is proposed to improve the resistance model at low bias current. The effect of self-heating on the sensor model is also considered.

A two-dimensional model is developed to explain the minority-carrier exclusion effect in circular Spreading-Resistance Temperature (SRT) sensor fabricated on thin silicon film. The model can be used to show the relation between minority-carrier exclusion length and maximum operating temperature of the sensor under different bias currents and different doping levels. Comparison is made between the proposed model and the conventional one-dimensional model used for similar sensors with rectangular shape. Experimental results show that the new model is more accurate than the one-dimensional model for predicting the characteristics of the circular SRT sensor.

A high-current injection phenomenon was found in Spreading-Resistance Temperature (SRT) sensor on SOI. Simulation and experiment of the sensor with different silicon-film thicknesses and doping concentrations were conducted to demonstrate this phenomenon, which can be explained by the conductivity modulation model normally used in LIGBT. This study is very helpful for designing the operating current of SRT sensor on SOI.

In this work, thermal resistors based on a simple rectangular structure are fabricated on three kinds of substrates thin-film (0.1 /spl mu/m) silicon-on-insulator (SOI), thick-film (10 /spl mu/m) SOI and bulk Si, and their characteristics are investigated. Measurements verify that SOI can indeed have additional freedom for increasing the maximum operating temperature (T/sub max/). More importantly, the thin-film SOI thermal resistor not only achieves a T/sub max/ as high as 420/spl deg/C, but also a low operating current of 1 /spl mu/A, which is about 1,000 times smaller than that of the thick-film SOI counterpart for the same T/sub max/. In conclusion, silicon resistor on SOI is a promising low-cost thermal sensor for a broad scope of low-power high-temperature applications.

This paper shows some technique about fabrication and analysis of electret back-plates in a kind of special microphones, which are used in measurement of sound wave. The sample of Teflon-FEP film (25 um thick) is deposited on the surface of the back-electrode of metal. Based on experimental results of the surface potential decay of electret samples, we use the method of high temperature extrapolation to calculate the active energy of trapped electrons. The result of experiments of surface potential decay is coincident with the theoretical analysis.

The effects of interlayer polarization in the preparation of electret are studied in this paper. We have deeply discussed several different samples by different ways, which is meaningful for the research of mini electret devices.

When a super-thin film electret is evaporated with metal electrodes on two sides, the electrons in electrodes have the possibility of crossing potential area in film. Suppose the electrons obey Fermi-distribution, it is found that the tunnel current across the film depends on both exerted voltage between the film and the thickness of the film. The temperature and work function of electrode-metal also have significant effects on the current. If exerted electrical field is very large, the result of calculation shows that the current can be proportional to exerted voltage in certain conditions.

Several highly nonlinear relations between disturbed surface acoustic wave (DSAW) and piezoelectric surface mount stress (PSMS) properties, temperature changes and electrode heights are computationally discovered, and quantitatively determined using a special new and effective perturbed multivariable thermal piezoelectric generalized plane strain finite element method (GPS FEM) with well-based shift and element static-condensation by improving plate element accuracies, in order to establish operating stabilities and design various potential high quality SAW resonating devices. Through executing the new codes on PC and Unix platforms, some new exclusive and fundamental results are included and provided.