Thermal annealing behaviour of Pt on n-GaN Schottky contacts

The structural evolution and temperature dependence of the Schottky barrier heights of Pt contacts on n-GaN epilayer at various annealing temperatures were investigated extensively by Rutherford backscattering spectrometry, x-ray diffraction measurements, Auger electron spectroscopy, scanning electron microscopy and current-voltage measurements. The temperature dependence of the Schottky barrier heights may be attributed to changes of surface morphology of Pt films on the surface and variation of nonstoichiometric defects at the interface vicinity. Experimental results indicated the degradation of Pt contacts on n-GaN above 600 degreesC.

Study on the reverse characteristics of Ti/6H-SiC Schottky contacts

The reverse I(V) measurement and analytic calculation of the electron transport across a Ti/6H-SiC Schottky barrier are presented. Based on the consideration of the barrier fluctuations and the barrier height shift caused by image charge and the applied voltage drop across Ti/SiC interfical layer, a comprehensive analytical model for the reverse tunneling current is developed using a WKB calculation of the tunneling probability through a reverse biased Schottky barrier. This model takes into account the main reverse conduction mechanism, such as field emission, thermionic field emission and thermionic emission. The fact that the simulated results are in good agreement with the experimental data indicates that the barrier height shift and barrier fluctuation can lead to reverse current densities orders of magnitude higher than that obtained from a simple theory. It is shown that the field and thermionic field emission processes, in which carries can tunnel through the barrier but cannot surmount it with insufficient thermal energy, dominate the reverse characteristics of a SiC Schottky contacts in a normal working condition.

Influence of annealed ohmic contact metals on electron mobility of strained AlGaN/GaN heterostructures

The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas (2DEG) is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors (AlGaN/GaN HFETs). Current-voltage (I-V) characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage (C-V) characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.

INFLUENCE OF THE OHMIC POLARIZATION EFFECT ON THIN-LAYER SPECTROELECTROCHEMISTRY

The influence of thin-layer resistance in cyclic voltammetry was studied in detail. Under the experimental conditions, a linear relationship between the peak-peak potential difference and the product of the peak current and the resistance was obtained and

Influenza vaccination of household contacts of newborns: a hospital-based strategy to increase vaccination rates.

We implemented a hospital-based influenza vaccination program for household contacts of newborns. Among mothers not vaccinated prenatally, 44.7% were vaccinated through the program, as were 25.7% of fathers. A hospital-based program provided opportunities for vaccination of household contacts of newborns, thereby facilitating better adherence to national vaccination guidelines.

Tungsten Silicide Contacts to Polycrystalline Silicon and Silicon-Germanium Alloys

Novel CVD WSi2 technology with low series and contact resistance in SiGe HBTs was achieved. Specific contact resistance to Si1-xGex with 0

Current-induced transition in atomic-sized contacts of metallic alloys

We have measured conductance histograms of atomic point contacts made from the noble-transition-metal alloys CuNi, AgPd, and AuPt for a concentration ratio of 1:1. For all alloys these histograms at low-bias voltage (below 300 mV) resemble those of the noble metals, whereas at high bias (above 300 mV) they resemble those of the transition metals. We interpret this effect as a change in the composition of the point contact with bias voltage. We discuss possible explanations in terms of electromigration and differential diffusion induced by current heating.

Current-driven magnetic rearrangements in spin-polarized point contacts

A method for investigating the dynamics of atomic magnetic moments in current-carrying magnetic point contacts under bias is presented. This combines the nonequilibrium Green's function (NEGF) method for evaluating the current and the charge density with a description of the dynamics of the magnetization in terms of quasistatic thermally activated transitions between stationary configurations. This method is then implemented in a tight-binding (TB) model with parameters chosen to simulate the main features of the electronic structures of magnetic transition metals. We investigate the domain wall (DW) migration in magnetic monoatomic chains sandwiched between magnetic leads, and for realistic parameters find that collinear arrangement of the magnetic moments of the chain is always favorable. Several stationary magnetic configurations are identified, corresponding to a different number of Bloch walls in the chain and to a different current. The relative stability of these configurations depends on the geometrical details of the junction and on the bias; however, we predict transitions between different configurations with activation barriers of the order of a few tens of meV. Since different magnetic configurations are associated with different resistances, this suggests an intrinsic random telegraph noise at microwave frequencies in the I-V curves of magnetic atomic point contacts at room temperature. Finally, we investigate whether or not current-induced torques are conservative.

Magnetomechanical interplay in spin-polarized point contacts

We investigate the interplay between magnetic and structural dynamics in ferromagnetic atomic point contacts. In particular, we look at the effect of the atomic relaxation on the energy barrier for magnetic domain wall migration and, reversely, at the effect of the magnetic state on the mechanical forces and structural relaxation. We observe changes of the barrier height due to the atomic relaxation up to 200%, suggesting a very strong coupling between the structural and the magnetic degrees of freedom. The reverse interplay is weak; i.e., the magnetic state has little effect on the structural relaxation at equilibrium or under nonequilibrium, current-carrying conditions.

Management of varicella contacts in pregnancy: VZIG or Vaccination?

Background Varicella infection during pregnancy poses a serious risk for both foetus and mother. It has been suggested that it would be more cost-effective to screen antenatally with post-partum vaccination, which occurs in the US, than the current policy of checking immune status post varicella exposure, with VZIG administration where necessary. Additionally, it is doubtful whether the current policy provides best patient care, when a vaccine is available. Objectives The study aims to retrospectively compare the cost of the current policy with a cost estimate for antenatal screening with post-partum vaccination in NI. Study design A cost estimate of antenatal screening of primigravidas, with post-partum vaccination, was calculated for two models: (1) verbal screening, with serological testing of those with no history of varicella infection and (2) serological screening of all primigravidas. Results The cost of VZIG issued to pregnant women in 2006 was £100,800; 43% of births were to primigravidas therefore the estimated cost of VZIG issued to multigravidas was £58,100. The cost of verbal screening with post-partum vaccination is estimated at £23,750 p.a., saving £34,350 over current policy. The estimated cost of screening all primigravidas with post-partum vaccination is £43,000, saving £15,100. Conclusions This retrospective study suggests that in NI either of the proposed antenatal screening strategies would be less costly than current practice. This finding supports the suggestion that varicella immunity testing should be included in the Antenatal Infectious Diseases Screening Programme, either as part of the universal vaccination programme or solely as an antenatal programme.

Extended contact effects as a function of closeness of relationship with ingroup contacts

Using survey data from Catholics and Protestants in Northern Ireland (N = 428), the authors examined the effects of extended contact via different types of ingroup contacts (neighbors, work colleagues, friends, and family members) and tested whether closeness to ingroup contacts moderated the effects of extended contact on outgroup trust. Results demonstrated that extended contact effects varied as a function of the relationship to ingroup contacts, and that extended contact interacted with closeness ratings in predicting outgroup trust. Consistent with hypotheses, extended contacts via more intimate ingroup relationships (i.e., friends and family) were overall more strongly related to outgroup trust than extended contacts via less intimate ingroup relations (i.e., neighbors and work colleagues). Moreover, within each level of intimacy extended contact was related to outgroup trust only at high, and not at low, levels of rated closeness to ingroup contacts. The theoretical contributions, limitations and practical implications of these findings are discussed.