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Characterizing interface trap states in commercial wide bandgap devices using frequency-based measurements requires unconventionally high probing frequencies to account for both fast and slow traps associated with wide bandgap materials. The C − ψ S technique has been suggested as a viable quasi-static method for determining the interface trap state densities in wide bandgap systems, but the results are shown to be susceptible to errors in the analysis procedure. This work explores the primary sources of errors present in the C − ψ S technique using an analytical model that describes the apparent response for wide bandgap MOS capacitor devices. Measurement noise is shown to greatly impact the linear fitting routine of the 1 / C S ∗ 2 vs ψ S plot to calibrate the additive constant in the surface potential/gate voltage relationship, and an inexact knowledge of the oxide capacitance is also shown to impede interface trap state analysis near the band edge. In addition, a slight nonlinearity that is typically present throughout the 1 / C S ∗ 2 vs ψ S plot hinders the accurate estimation of interface trap densities, which is demonstrated for a fabricated n-SiC MOS capacitor device. Methods are suggested to improve quasi-static analysis, including a novel method to determine an approximate integration constant without relying on a linear fitting routine. [ABSTRACT FROM AUTHOR]

Antiferromagnetic coupling between rare-earth (RE) and transition metals (TM) gives rise to various magnetic ground states in RE/TM heterostructures. Interface structure and morphology tend to play important roles in defining the magnetic properties of heterostructures of these materials. Using spin-dependent polarized neutron reflectivity (PNR), we found a distinct magnetic structure for RE/TM (Gd/Co) multilayers having different interface morphologies. Two Gd/Co multilayers, each consisting of eight bilayers of Gd and Co, were grown at different argon pressures to accomplish variation in the interface morphology. The Gd/Co multilayer, which is grown at a lower argon pressure, exhibits lower intermixing/interdiffusion at the interfaces and shows asymmetric magnetic hysteresis loops below the compensation temperature (Tcomp ∼ 140 K) and antisymmetric magnetoresistance at Tcomp. The other multilayer, grown at two different argon pressures for the top and bottom four bilayers, shows a double hysteresis loop with an exchange-bias-like shift to the field axis at temperatures above Tcomp (∼150 K). From PNR measurements across Tcomp, these behaviors were attributed to interface dependent magnetic helical structures. The PNR results indicate the formation of a twisted helical magnetic structure with planar 2π domain walls and the evolution of magnetic inhomogeneities below Tcomp. The interface dependent twisted helical magnetic structures and the development of highly correlated magnetic inhomogeneities may find applications in all-spin-based technologies. [ABSTRACT FROM AUTHOR]

We investigate electron transport in epitaxially grown nitride-based resonant tunneling diodes (RTDs) and superlattice sequential tunneling devices. A density-matrix model is developed, and shown to reproduce the experimentally measured features of the current–voltage curves, with its dephasing terms calculated from semi-classical scattering rates. Lifetime broadening effects are shown to have a significant influence in the experimental data. Additionally, it is shown that the interface roughness geometry has a large effect on current magnitude, peak-to-valley ratios and misalignment features; in some cases eliminating negative differential resistance entirely in RTDs. Sequential tunneling device characteristics are dominated by a parasitic current that is most likely to be caused by dislocations; however, excellent agreement between the simulated and experimentally measured tunneling current magnitude and alignment bias is demonstrated. This analysis of the effects of scattering lifetimes, contact doping and growth quality on electron transport highlights critical optimization parameters for the development of III–nitride unipolar electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The anomalous appearance of a ferromagnetic moment in nominally antiferromagnetic nanoparticles has been known about since Néel, but never well understood. We present proof of the core/shell model of magnetism in antiferromagnetic NiO nanoparticles (NP) using neutron diffraction. Nickel oxide nanoparticles were produced in a large quantity by a novel continuous hydrothermal flow synthesis method. The antiferromagnetic nature of the nanoparticles allowed the structural and the magnetic diffraction peaks to be completely separated. Using both the microstructure option in "Fullprof" microstructure fitting suite and convolution techniques, we determined the NP consisted of an ordered antiferromagnetic core 5.2(2) nm in diameter surrounded by a disordered shell 0.7(2) nm thick. Further magnetic measurements showed that this disordered shell possess a significant polarisable magnetisation, up to a fifth that of pure nickel. They also indicate that two magnetic transitions occur between 400 and 10 K; around 350 K, there is a broad transition from paramagnetic to a form of superparamagnetism, then near 30 K there is a transition to a higher anisotropy state. Differences in field cooled and zero field cooled hysteresis loops were found, though with no evidence of exchange bias effects. [ABSTRACT FROM AUTHOR]

The nonparabolic Schrödinger equation for electrons in quantum cascade lasers (QCLs) is a cubic eigenvalue problem (EVP) which cannot be solved directly. While a method for linearizing this cubic EVP has been proposed in principle for quantum dots [Hwang et al., Math. Comput. Modell., 40, 519 (2004)] it was deemed too computationally expensive because of the three-dimensional geometry under consideration. We adapt this linearization approach to the one-dimensional geometry of QCLs, and arrive at a direct and exact solution to the cubic EVP. The method is then compared with the well established shooting method, and it is shown to be more accurate and reliable for calculating the bandstructure of mid-infrared QCLs. [ABSTRACT FROM AUTHOR]

A design of a biological molecule carrier is presented for the application of high throughput multiplexing biological assays. This carrier contains a bit addressable “magnetic barcode” made of either Permalloy or cobalt thin films, sandwiched between two planar SU8 protective layers. We describe how the design of the magnetic carriers is optimized by engineering the coercivity of each barcode element, allowing the number of available signatures to be increased. Fully encapsulated digital magnetic carriers which carry a 5 bit addressable barcode were also fabricated and are presented. Writing and reading of digital carriers were both performed after releasing in dried solution. [ABSTRACT FROM AUTHOR]

Discusses the fabrication and electrical performance of an all refractory niobium-nitrogen medium scale integrated circuit process. Fabrication of Josephson junctions; Plasma etching of in situ radio frequency sputter deposited trilayers of niobium-nitrogen/magnesium-oxygen/niobium-nitrogen; Use of a deposited silicon dioxide film for wiring and resistor insulation.

Presents a study which described the low-level pretunneling leakage currents and the measurement techniques needed to determine the properties of the excess leakage currents associated with the traps generated inside of the oxide. Components of current which were identified; Unstressed current-voltage characteristics; Stressed current-voltage characteristics.

Focuses on a study which characterized the SiO[sub2]/SiC interface through the high-low capacitance-voltage and conductance-frequency techniques. Experimental details; Results and discussion; Summary.

Presents a study that described electrical measurement on exposed surfaces of n- and p-type gallium arsenide. Features of the n-type surface; Features of the p-type gallium arsenide; Significance of the findings for gallium arsenide devices.

Presents a study which demonstrated that thermal generation rates in gallium arsenide can increase by more than three orders of magnitude when samples are metallized in E-beam evaporators rather than in thermal evaporators. Device fabrication; Measurement technique; Experimental results; Activation energy of the control sample.

Presents a study that examined the photocapacitance-voltage and current-voltage characteristics of p[sup+]-gallium arsenide/i-alimunum arsenide/n-gallium arsenide heterojunction enhancement mode capacitors. Analysis of the constant illumination of the capacitor; Determination of the constant reverse sweep rate; Evaluation of the frequency dependence of the capacitor.

Presents a study which investigated the collisionally induced line shapes corresponding to an electric quadropole transition in neutral calcium for a variety of rare-gas perturber species. Experimental details; Interpretation of the results in terms of molecular potentials; Conclusion.

Presents results of experiments probing the effect of collisions on forbidden lines. Classes of transitions of low oscillator strength in many atoms; Description of collisions between radiators and perturbers via an interaction; Blue wing of the collisionally induced signal for the calcium/argon collision complex.

Microarrays and suspension-based technologies have attracted significant interest over the past decade with applications in medical diagnostics and biochemical multiplexed assays. However, the throughput of microarrays will always be limited by the array density and the slow kinetics, while the suspension (or bead)-based technologies are currently limited by the number of distinct codes the beads can carry. A novel digital magnetic tagging technology based on magnetic tags that can be used as encoded microcarriers for biomolecular probes, is presented here. The highly disruptive platform technology can provide a very large number of unique codes, enabling a high degree of multiplexing. The design principles of a novel magnetic laboratory-on-a-chip device comprising microfluidic channels with embedded magnetic tunneling magnetoresistive sensors are also discussed. [ABSTRACT FROM AUTHOR]

Focuses on a study that detailed the measurement of capacitance-time transients on n-type 6H-silicon carbide (SiC) metal-oxide semiconductor (MOS) capacitors. Purpose of conducting the measurement; Result that occurred due to the high band gap energy of SiC; Properties in which SiC is unusual; Key element in MOS devices.

Provides information on a study concerning the fabrication of gate-controlled diodes in the wide band gap semiconductor 6hydrogen-silicon carbon by thermal oxidation and ion implantation of nitrogen. Discussion of the nonequilibrium characteristics of diodes; Room-temperature capacitance-voltage characteristics; Surface state density.