An investigation of the origin of the main electron trap in GaAs

The origin of the main electron trap (0.83 eV) in GaAs is investigated by creating conditions to favour the formation of Ga-vacancy-oxygen complex in the material. Two specific schemes have been used, (1) Liquid phase epitaxial (LPE) growth of the material at high temperatures (≈1000°C) with oxygen doping and (2) Electron bombardment of LPE material and subsequent annealing. The traps have been characterised by transient capacitance technique. The results show that the main electron trap cannot be produced by either of the schemes thereby implying that a complex involving Ga-vacancy and oxygen may not be responsible for the trap.     

Spatial distribution of power coupling in self-pumped photorefractive reflection gratings

The spatial distribution of the power transfer achieved by contradirectional two-beam coupling using self-pumped photorefractive reflection gratings is investigated in two materials with different photorefractive gain coefficients, LiNbO3:Fe and KNbO3:Fe. Incremental portions of the volume grating are erased optically by inducing thin optical damage planes, reducing the overall two-beam coupling efficiency. By monitoring the effect of local grating disruption, the distribution of power transfer is spatially resolved throughout the crystal, and the results are found to be in agreement with our theoretical predictions.     

Phase equilibria in the system BaO-CeO2

The phase equilibrium relationships in the binary system BaO-CeO₂ have been investigated by thermal analysis, metallographic and X-ray diffraction methods. The system is characterised by the existence of only one compound, namely, BaCeO₃ which is found to melt incongruently at 1480±5°C with formation of solid CeO₂ and a liquid. A eutectic is found to occur between BaO and BaCeO₃ at 46±0.5 mol% CeO₂ and its melting point was determined as 1440±5°C. A narrow solid solubility range of BaO in BaCeO₃ exists but no solid solubility of BaCeO₃ in either BaO or CeO₂ was detected.     

Amorphous hydrogenated silicon films prepared from a glowdischarge

From a detailed study of electrical and optical properties of amorphous hydrogenated silicon prepared from a mixture of 10% silane and 90% hydrogen, it is shown that the properties of the films compare favourably with the best reported results on those prepared from 100% silane.     

Interface effects in YBCO/(Y-Pr)BCO multilayers, and the dimensionality of high-Tc superconductivity

Measurements on YBCO/(Y-Pr)BCO trilayers show that the depression of the transition temperature in ultrathin YBCO is accompanied by a decrease in the conductance of the layers adjacent to the interfaces. The lowering of the conductance seems to be primarily the result of charge transfer across the interfaces, and perhaps to some extent also of defects. The intrinsic properties of YBCO seem to change little or not at all as the thickness decreases from bulk down to that of a single unit cell.     

Synthesis and characterization of highly acetylated sago starch

This study was carried out to understand and establish the changes in physicochemical parameters of sago starch after acetylation. Highly substituted starch acetate was prepared by reaction with native sago starch and acetic anhydride in organic solvent. Their formation was confirmed by the titrimetric analysis and FT‐IR. The presence of absorption band in FT‐IR at 1748 cm⁻¹ confirmed the carbonyl group attachment. The thermal behavior of native and acetyl substituted sago starch was investigated using thermo gravimetric analysis (TGA) and DSC. The results reveal that highly substituted starch acetate was more thermally stable as compared to native form. The XRD patterns showed loss of crystalline nature and its transformation into amorphous form. The SEM study suggested that the smooth surfaces of starch granules were changed into fibrous form after acetylation.     

High performance wire‐array silicon solar cells

Nano/micro‐wire silicon solar cells, consisting of wire‐arrays of radial p–n junction structures, are expected to offer performance enhancement at lower costs, using smaller volumes of low carrier lifetime, cheaper silicon. Using inexpensive microsphere‐lithography‐based fabrication that is scalable to large areas, we have demonstrated wire‐array solar cells that outperform the control cell. Key to the design of these cells is the impact of various parameters, such as wire diameter and junction depth, that influences the competing effects of light trapping ability of the wire‐array, quantum efficiency, and series resistance of the resulting device. Using capacitance measurements we can identify two possible types of junction structure in a wire‐array solar cell: radial and planar. We show that the former is the prerequisite for performance‐enhancing wire‐array solar cells. Copyright © 2010 John Wiley & Sons, Ltd.     

Survey on various architectures of preamplifiers for electroencephalogram (EEG) signal acquisition

Microsystem Technologies - Modern-day biomedical science and technology have progressed with implantable neural recording systems. There is a demand for miniaturised devices that can be emplaced...     

A single variable shear deformable nonlocal theory for transversely loaded micro- and nano-scale rectangular beams

In this paper, a simple single variable shear deformable nonlocal theory for bending of micro- and nano-scale rectangular beams is presented. To incorporate small size effects, the theory uses Eringen’s nonlocal differential constitutive relations. The theory has only one fourth-order governing differential equation involving a single unknown variable. The governing equation and the expressions for the bending moment and shear force of the present theory are strikingly similar to those of nonlocal Euler-Bernoulli Beam Theory (EBT) formulated based on Eringen’s nonlocal elasticity theory. The theory assumes that the axial and lateral displacements have bending and shear components such that the bending components do not contribute towards shear force, and the shear components do not contribute towards bending moment. Also, the chosen displacement functions of the theory give rise to a realistic parabolic transverse shear stress distribution across the beam cross-section. Efficacy of the proposed theory is demonstrated through bending of simply supported, cantilever and clamped-clamped micro- and nano-scale beams of rectangular cross-section. The numerical results obtained by using the present theory are compared with those predicted by other nonlocal first-order and higher-order shear deformation beam theories. The results obtained are quite accurate.