Spin transport in self assembled all-metal nanowire spin valves: a study of the pure Elliott-Yafet mechanism

We report experimental study of spin transport in all metal nanowire spin valve structures. The nanowires have a diameter of 50 nm and consist of three layers--cobalt, copper, and nickel. Based on the experimental observations, we determine that the primary spin relaxation mechanism in the paramagnet layer--copper--is the Elliott-Yafet mode associated with elastic scattering caused by charged states on the surface of the nanowires. This mode is overwhelmingly dominant over all other modes, so that we are able to study the pure Elliott-Yafet mechanism in isolation. We deduce that the spin diffusion length associated with this mechanism is about 16 nm in our nanowires and is fairly temperature independent in the range 1-100 K, which is consistent with the spin relaxation being associated with elastic scattering by surface states. The corresponding spin relaxation time is about 100 femtoseconds. We also find that the spin relaxation rate is fairly independent of the electric field driving the current in the field range 0.3-3 kV/cm.     

Wearable and Miniaturized Sensor Technologies for Personalized and Preventive Medicine

The unprecedented medical achievements of the last century have dramatically improved our quality of life. Today, the high cost of many healthcare approaches challenges their long‐term financial sustainability and translation to a global scale. The convergence of wearable electronics, miniaturized sensor technologies, and big data analysis provides novel opportunities to improve the quality of healthcare while decreasing costs by the very early stage detection and prevention of fatal and chronic diseases. Here, some exciting achievements, emerging technologies, and standing challenges for the development of non‐invasive personalized and preventive medicine devices are discussed. The engineering of wire‐ and power‐less ultra‐thin sensors on wearable biocompatible materials that can be placed on the skin, pupil, and teeth is reviewed, focusing on common solutions and current limitations. The integration and development of sophisticated sensing nanomaterials are presented with respect to their performance, showing exemplary implementations for the detection of ultra‐low concentrations of biomarkers in complex mixtures such as the human sweat and breath. This review is concluded by summarizing achievements and standing challenges with the aim to provide directions for future research in miniaturized medical sensor technologies.     

A novel rock-like nanoarchitecture of YVO4:Eu3+ phosphor: selective synthesis, characterization, and luminescence behavior

A facile, surfactant-mediated strategy involving ‘oriented attachment’ assisted self-assembly of rice-like and grape-like nanostructures resulted into a novel encapsulated rock-like luminescent YVO₄:Eu³⁺ nanoarchitecture in aqueous medium. It is shown that a characteristic crystallization behavior of YVO₄:Eu³⁺ leads to the growth of a rice-like shape in a template-free reaction system. In presence of a surfactant, these rice-like structures in the vicinity of the micellar head groups self-assemble to form nanograpes and ultimately produce rock-like nanostructures upon prolonged autoclaving. The rock-like nanocrystalline phosphors, having an average area of 2798 nm², are composed of an inner nucleus and a surrounding shell-like cover, as evidenced from the transmission electron microscopy images. Finally, the room temperature photoluminescence spectra demonstrate that the morphology of the nanophosphors has immense influence on their chromaticity.     

Effect of compaction on the kinetics of thermal decomposition of dolomite under non-isothermal condition

Many workers [1–9] studied the kinetics of dolomite decomposition to study the effects of different parameters like, gas (CO₂, N₂ etc.) pressures, water vapor, presence of other impurities, particle size and grain size of the dolomite samples, crystallinity etc. on the decomposition kinetics of dolomite using different tools like, thermal analysis, thermo-gravimetric analyses, XRD technique etc. and different values of the activation energies for the decomposition reaction, order of reactions have been reported. It has been observed that pure dolomite decomposed in only two steps. The first stage of the thermal decomposition of dolomite resulted in the formation of Mg-calcite [(CaMg)CO₃] and periclase (MgO), with the liberation of CO₂. It was further observed that under CO₂, dolomite decomposed directly to CaCO₃, accompanied by the formation of MgO between 550 and 765^∘C. Calcite decomposed to CaO between 900 and 960^∘C and under air, simultaneous formation of CaCO₃, CaO and MgO accompanied dolomite decomposition between 700 and 740–750∘C. At the latter temperature, the calcite began to decompose even though a significant amount of dolomite was still present and simultaneous decomposition of the two carbonates was terminated at 780^∘C. Also, changes in decomposition rates of the various phases correlated with changes in the rate of weight loss determined by derivative thermo-gravimetric analysis.     

Electrical Discharge Machining of MMCs Reinforced with Very Small Particles

This paper investigates material removal rate (MRR), kerf width, surface finish, and electrode wire wear for different pule-on-times as well as wire tensions during EDM of 6061 aluminum alloy reinforced with 10 vol % 700 nm SiCp MMC. Effects of pulse-on-time on output variables at lower and higher wire tensions were investigated. Similarly, effects of the wire tensions on output variables at shorter and longer pulse-on-times were also investigated. Longer pule-on-time increases the MRR though the higher wire tension reduces the MMR. The effect of wire tension on MRR is much more significant at longer pule-on-time compare to that at shorter pule-on-time. There is an optimum pule-on-time for which best surface finish is achieved. The surface finish deteriorates when the pulse-on-time is higher or lower than the optimum pule-on-time. With the rise of tension in wire, the surface roughness increases and decreases at shorter and longer pule-on-times, respectively. The machined surface contains solidified molten material, splash of materials, and blisters. Generation of the tapered slot with higher kerf width at the top indicates the wear of wire electrode. Significant variation of the electrode wire diameter was due to coating of the matrix, wear, and clogging of small reinforced particles in the electrode gap.     

Effect of annealing on the fracture behavior of La0.58Sr0.4Co0.8Fe0.2O3‐δ, a potential energy material for oxygen separation

The perovskite material La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ, offers high oxygen permeability at elevated temperature and is considered as a potential material for oxygen separation membranes. It can enhance the efficiency of oxy‐fuel combustion at high temperatures (> 800 °C) and hence due to the high reliability demands, required by the long term operation at elevated temperatures, it requires a thorough investigation from the view point of structural stability. Aiming towards long term stability, the present work is a detailed and systematic study on the effect of annealing on the mechanical behavior of dense La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ. The study reveals that the indentation fracture toughness of the material increases with increase in annealing temperature. In most of the indentation loads, the subsurface crack profile was Palmqvist in nature with low value of the ratio of crack length versus indentation size (c/a). A consistent pattern of variation of c/a and indentation fracture toughness (K_IC) at all indentation loads was observed. Systematic drop in c/a and subsequent increase in fracture toughness in the as prepared test pieces has been attributed to residual stress accumulation during preparation.     

Optimization of Epoxy-Barium Titanate Nanocomposites for High Performance Embedded Capacitor Components

One of the most promising avenues to meet the requirements of higher performance, lower cost, and smaller size in electronic systems is the embedded capacitor technology. Polymer-ceramic nanocomposites can combine the low cost, low temperature processability of polymers with the desirable electrical and dielectric properties of ceramic fillers, and have been identified as the major dielectric materials for embedded capacitors. However, the demanding requirements of mechanical properties and reliability of embedded capacitor components restrict the maximum applicable filler loading (<50vol%) of nanocomposites and thereby limit their highest dielectric constants (<50) for real applications. In this paper, we present a study on the optimization of the epoxy-barium titanate nanocomposites in order to obtain high performance, reliable embedded capacitor components. To improve the reliability of polymer-ceramic nanocomposites at a high filler loading, the epoxy matrix was modified with a secondary rubberized epoxy, which formed isolated flexible domains (island) in the continuous primary epoxy phase (sea). The effects of sea-island structure on the thermal mechanical properties, adhesion, and thermal stress reliability of embedded capacitors were systematically evaluated. The optimized, rubberized nanocomposite formulations had a high dielectric constant above 50 and successfully passed the stringent thermal stress reliability test. A high breakdown voltage of 89MV/m and a low leakage current of about 1.9times10^-11A/cm² were measured in the large area thin film capacitors     

Cutting performance of diamond tools during ultra-precision turning of electroless-nickel plated die materials

This study is an attempt (a) to observe the wear characteristic of diamond tool with 200 km cutting distance and to study the effects of wear on the surface roughness and cutting forces and (b) to optimize various cutting parameters such as depth of cut, feed rate, spindle speed and phosphorus content. The experimental results showed that tool wear was not so significant although some defects on rake face were observed after cutting 15.6 km. Further cutting showed that the surface roughness increases with cutting distance, and that the cutting forces were larger than thrust force at the beginning of cutting, but after cutting 130 km, thrust force became larger and increased rapidly. It was also observed that forces increase with the increase of depth of cut, spindle speed and feed rate, and decrease with the increase of phosphorus content of the plating. Depth of cut has no significant effect on surface roughness, while it increases with increase of feed rate and decreases with the increase of percentage of phosphorus content in the workpieces. In case of spindle speed, surface roughness decreases with the increase of spindle speed up to a certain value and then starts to increase with the increase of spindle speed.     

A Study on Process Parameters of Direct Ethanol Fuel Cell

Ethanol is one of the promising future fuels of Direct Alcohol Fuel Cells (DAFC). The electro‐oxidation of ethanol fuel on anode made of carbon‐supported Pt‐Ru electrode catalysts was carried out in a lab scale direct ethanol fuel cell (DEFC). Cathode used was Pt‐black high surface area. The membrane electrode assembly (MEA) was prepared by sandwiching the solid polymer electrolyte membrane, prepared from Nafion^® (SE‐5112, DuPont USA) dispersion, between the anode and cathode. The DEFC was fabricated using the MEA and tested at different catalyst loadings at the electrodes, temperatures and ethanol concentrations. The maximum power density of DEFC for optimized value of ethanol concentration, catalyst loading and temperature were determined. The maximum open circuit voltage (OCV) of 0.815 V, short circuit current density (SCCD) of 27.90 mA/cm² and power density of 10.30 mW/cm² were obtained for anode (Pt‐Ru/C) and cathode (Pt‐black) loading of 1 mg/cm² at a temperature of 90°C anode and 60°C cathode for 2M ethanol.     

Surface modification of low‐density polyethylene films by a novel solution base chemical process

The surfaces of the film samples of low‐density polyethylene (LDPE) were chemically modified with an aqueous solution of ammonium persulphate solution (0.1 M) and Fe (NO₃)_3,9H₂O (0.2 M) heated to about 80°C for 2.5 h for which polar groups like ? OH, 〉CO, ? COOH, etc., were generated on the surface of the LDPE films. The modified films were analyzed by Infrared (IR) spectroscopy, Scanning Electron Microscopy (SEM), and Electron Spectroscopy for Chemical Analysis (ESCA). New surface of LDPE produced by this modification, demonstrated reasonable oxygen incorporation on the surface of polymer films through chemical bonding, which is essential for adhesion processes. For these chemical changes the extent of printability and adhesion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3046–3051, 2004