Abstract: Two concentric two-dimensional GaAs/(Al,Ga)As nanorings in a normal magnetic field are theoretically studied. The single-band effective mass approximation is adopted for both the electron and the hole states, and the analytical solutions are given. We find that the electronic single particle states are arranged in pairs, which exhibit anticrossings and the orbital momentum transitions in the energy spectrum when magnetic field increases. Their period is essentially determined by the radius of the outer ring. The oscillator strength for interband transitions is strongly reduced close to each anticrossing. We show that an optical excitonic Aharonov-Bohm effect may occur in concentric nanorings.

Abstract: Tunnel field-effect transistors (TFETs) are potential successors of metal-oxide-semiconductor FETs because scaling the supply voltage below 1 V is possible due to the absence of a subthreshold-swing limit of 60 mV/decade. The modeling of the TFET performance, however, is still preliminary. We have developed models allowing a direct comparison between the single-gate, double-gate, and gate-all-around configuration at high drain voltage, when the drain-voltage dependence is negligible, and we provide improved insight in the TFET physics. The dependence of the tunnel current on device parameters is analyzed, in particular, the scaling with gate-dielectric thickness, channel thickness, and dielectric constants of gate dielectric and channel material. We show that scaling the gate-dielectric thickness improves the TFET performance more than scaling the channel thickness and that improvements are often overestimated. There is qualitative agreement between our model and our experimental data.

Abstract: The capacitance-voltage (C-V) characteristic is calculated for p-type In_0.53Ga_0.47As metal-oxide-semiconductor (MOS) structures based on a self-consistent PoissonSchrödinger solution. For strong inversion, charge quantization leads to occupation of the satellite valleys which appears as a sharp increase in the capacitance toward the oxide capacitance. The results indicate that the charge quantization, even in the absence of interface defects (D_it), is a contributing factor to the experimental observation of an almost symmetric C-V response for In_0.53Ga_0.47As MOS structures. In addition, nonparabolic corrections are shown to enhance the depopulation of the Γ valley, shifting the capacitance increase to lower inversion charge densities.

Abstract: The electronic properties of a set of intrinsic and extrinsic point defects in gamma-Al2O3 are investigated using quasiparticle calculations within the G(0)W(0) approximation. We find that the electronic signature of atomic vacancies lie deep in the band gap, close to the top of the valence band edge. The introduction of C, Si, and N impurities induces defective levels that are located close to the conduction band edge and near the middle of the band gap of the oxide. The comparison with electrical measurements reveals that the energy levels of some of these defects match with the electronic fingerprint of the defects reported in gamma-Al2O3 based nonvolatile memories. (C) 2010 American Institute of Physics. [doi:10.1063/1.3507385]

Abstract: The cyclotron resonance (CR) absorption spectrum is calculated for a II-VI parabolic quantum dot (QD) containing few electrons and a single magnetic dopant (Mn(2+)). We find that Kohn's theorem no longer holds for this system and that the CR spectrum depends on the number of electrons inside the QD. The electron-Mn-ion interaction strength can be tuned for example by the magnetic field and by moving the Mn-ion to different positions inside the QD. We demonstrate that due to the presence of the Mn-ion the relative motion of the electrons couple with their center-of-mass motion through the electron-Mn-ion spin-spin exchange term resulting in an electron-electron interaction dependence of the magneto-optical absorption spectrum. At the ferromagnetic-antiferromagnetic transition we observe significant discontinuities in the CR lines.

Abstract: Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids.

Abstract: Multiple-step martensitic transformations of an aged Ni51Ti49 single crystal using calorimetric method were investigated. Results show that for short aging times (1045 min) multiple-step martensitic transformations on cooling occur in two steps. Applying intermediate aging times (1.254 h) results in three steps and long aging times (more than 8 h) lead to two-step martensitic transformations again. This behavior has not been recognized in NiTi single crystals in literatures. It can be related to the heterogeneity of composition and stress fields around Ni4Ti3 precipitates.

Abstract: This paper uses a mechanistic frontier approach as a reference to evaluate the ability of conventional parametric (SFA) and non-parametric (DEA) frontier approaches for analyzing economicenvironmental trade-offs. Conventional frontier approaches are environmentally adjusted through incorporating the materials balance principle. The analysis is worked out for the Flemish pig finishing case, which is both representative and didactic. Results show that, on average, SFA and DEA yield adequate economicenvironmental trade-offs. Both methods are good estimators for technical efficiency. Cost allocative and environmental allocative efficiency scores are less robust, due to the well-known methodological advantages and disadvantages of SFA and DEA. For particular firms, SFA, DEA and the mechanistic approach may yield different economicenvironmental trade-offs. One has therefore to be careful when using conventional frontier approaches for firm-specific decision support. The mechanistic approach allows for optimizing performances per average present finisher, which is the production unit in pig finishing. Conventional frontier methods do not allow for this optimization since the number of average present finishers varies along the production functions. Since the mechanistic production function is based on underlying growth, feed uptake and mortality functions, additional firm-specific indicators can also be calculated at each point of the production function.

Abstract: Laser ablation is used in a growing number of applications in various areas including medicine, archaeology, chemistry, environmental and materials sciences. In this work the heat transfer and phase change phenomena during nanosecond laser ablation of a copper (Cu) target in a helium (He) background gas at atmospheric pressure are presented. An enthalpy model is outlined, which accounts for heating, melting, and vaporization of the target. As far as we know, this is the first model that connects the thermodynamics and underlying kinetics of this challenging phase change problem in a selfconsistent way.

Abstract: The molecular character of atmospheric particulate matter is of prime importance when interpreting air pollution trends and its subsequent influence on environmental monitoring and preventative conservation. The known methods of estimating the molecular composition normally involve elemental analysis of particles (both as bulk and computer controlled analyses of single particles) with subsequent multivariate analyses to clusterise the elements in groups of elements that are closely related to each other. With this approach one can at best suggest associations. Evidently the application of molecular spectroscopy in addition to elemental concentration profiles would provide intimate information regarding the nature of the particles and consequently their fate. This paper gives an overview of research performed in our laboratory and describes the optimisation of experimental parameters to use scanning electron microscopy with energy-dispersive X-ray detection (SEM/EDX) or electron probe X-ray microanalysis (EPXMA) in parallel with micro-Raman Spectrometry (MRS) to investigate single environmental particles. The challenges associated with the two stand-alone techniques are revealed and consequently those posed with an interfaced approach are discussed. Preliminary results, of an initial investigation of the SEM/EDX interfaced with MRS to ultra-fine heterogeneous environmental particles, are given.

Abstract: Recent findings have linked low hysteresis in shape memory alloys with phase compatibility between austenite and martensite. To investigate the evolution of microstructure as phase compatibility increases and hysteresis is reduced, transmission electron microscopy was used to study the alloy system Ti50Ni50xPdx, where the composition is systemically tuned to approach perfect compatibility. Changes in morphology, twinning density and twinning modes are reported, along with special microstructures occurring when compatibility is achieved. In addition, the interface between austenite and a single variant of martensite was studied by high-resolution and conventional electron microscopy. The low energy configuration of the interface detailed in this article suggests that it plays an important role in the lowering of hysteresis compared to classical habit plane interfaces.