Applied Physics

In this article, performance of 70 W, 350 rpm, axial-field and radial-field permanent magnet brushless dc motors is compared using computer aided design (CAD) and finite element (FE) methods. The design variables like number of poles, slots per pole per phase, airgap length, airgap flux density, slot electric loading, stator flux density, and the permanent magnet material are changed one at a time and the performances are calculated using the developed CAD program. The CAD results are validated by carrying out two-dimensional and three-dimensional FE analyses. It is observed that the axial-field motor gives higher efficiency, whereas the radial-field motor has less weight.

Hysteresis behaviour of the current–voltage characteristics collected on spin coated synthetic eumelanin layer embedded in the Au/eumelanin/ITO/glass structure is shown. The effect has been observed under dark both in air and vacuum environment and its magnitude has been found related to the eumelanin hydration state. Moreover, in vacuum and under white light illumination, enhancement of the hysteresis loop area respect to those collected under dark has been observed. Space charge storage and charge trapping/detrapping as possible mechanisms responsible of the observed current–voltage behaviour are discussed. Preliminary experimental results have evidenced the possible integration of eumelanin layers in electro-optical charge storage based memory devices.

The melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high-temperature endotherm (T2M) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 220°C, while the lower-temperature endotherm (T1M) extrapolates to an ultimate melting point of 185°C. Noncrystalline chain orientation influences the endotherm temperature through its changing configurational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.

A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the InP energy gap, followed by strongly damped Franz-Keldysh oscillations (FKOs) which do not appear when the spectra are obtained at 77 K. The builtin electric field estimated from FKOs shows a small doping dependence but is substantially affected by the inclusion of a thin layer of AlxGayIn1-x-yAs (x≡0.22) at the interface between InP (Fe) and AlInAs:Si. In order to explain these results, a model based on the discontinuity of the energy bands in the InP/AlInAs and InP/AlGaInAs/AlInAs systems and also on the matching of the Fermi levels between the different materials is suggested.

Passive and remote sensing technology has many potential applications in implantable devices, automation, or structural monitoring. In this paper, a tri-layer thin film giant magnetoimpedance (GMI) sensor with the maximum sensitivity of 16%/Oe and GMI ratio of 44% was combined with a two-port surface acoustic wave (SAW) transponder on a common substrate using standard microfabrication technology resulting in a fully integrated sensor for passive and remote operation. The implementation of the two devices has been optimized by on-chip matching circuits. The measurement results clearly show a magnetic field response at the input port of the SAW transponder that reflects the impedance change of the GMI sensor.

Na-doped ZnO thin films were deposited on quartz substrates at various temperatures by using pulsed laser deposition technique. An X-ray diffractometer and an atomic force microscope were used to investigate the structural and morphological properties of the thin films. A Hall effect measurement system was used to investigate the electrical properties of the thin films. A spectrophotometer was used to measure the transmittances of the thin films. The band gap energies of the thin films were calculated by linear fitting the sharp absorption edge for high-quality thin film. The band gap energies of the Na-doped ZnO thin films are nearly the same as the pure ZnO. A spectrometer was used to investigate the luminescent properties of the thin films. The thin film deposited at 200 degrees C had no near band edge emission and no deep-level emission. The NBE emission appeared and increased with increasing the growth temperature.

The generalized plane strain solution for anisotropic multilayer nanostructures with cubic crystal symmetry under the influence of initial strains has been derived. This solution can be used to estimate equilibrium curvature radius and strains/stresses of rolled-up anisotropic multilayer nanostructures, whose deformations are induced by crystal lattice mismatch. The solution has been applied for calculation of curvature radii and strain components of a bilayer In0.2Ga0.8As/GaAs rolled-up nanostructure. The results are in agreement with those obtained by a finite element analysis.

Fluorinated and hydrogenated amorphous silicon‐carbon alloys (a‐SiC:H,F) are produced by glow discharge decomposition of SiF 4 ‐CH 4 ‐H 2 mixture. Small amount of CH 4 in SiF 4 ‐H 2 mixture are enough to produce silicon carbon alloys having optical gap ranging between 1.8 and 2.6 eV. Materials, having 1.95 eV band gap and exhibiting optoelectronic properties typical of state of art a‐SiC:H, are deposited under plasma modulation conditions. © 1996 American Institute of Physics.