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White organic light emitting diodes (WOLEDs) with both phosphorescent and fluorescent emitting layers (EML) usually adopt an interlayer between them to achieve high efficiency by preventing mutual quenching, but insertion of the interlayer causes a higher operating voltage as well as additional fabrication steps. Here, we demonstrate that simple-structure WOLEDs without an interlayer could be achieved using the combination of phosphor-sensitized-fluorescent red and phosphorescent blue EMLs. In addition, the main cause of the color shift with increasing current density was identified, and the color shift of the WOLED was successfully suppressed by properly balancing emission from the red and blue EMLs. Consequently, a maximum external quantum efficiency of 6.2% (a current efficiency of 14.3 cd/A) and very stable color coordinates of (0.32±0.01,0.42±0.002) were achieved. However, the elimination of an interlayer for the combination with a fluorescent blue EML causes about 50% decrease in the efficiency and a large change in the color coordinates with the driving current density. [ABSTRACT FROM AUTHOR]

Tunable photonic crystals that are based on acousto-optic effects were proposed in this paper. Theoretical analysis and numerical simulations were carried out for the tunable photonic crystals. According to the acousto-optic effect, acoustic waves propagating in elastic media induce periodic dielectric structures in the media, and thus the media can be used as photonic crystals. Such photonic crystals possess a prominent characteristic that the photonic band gaps can be changed real-timely by adjusting the acoustic intensity and frequency. The work done in this paper opens up a possibility to achieve tunable photonic crystals on the basis of acousto-optic effects. [ABSTRACT FROM AUTHOR]

A high refractive index of 2.231±0.001 at 1313 nm is achieved in a colorless, transparent spherical La4Ti9O24 glass that was prepared by using an aerodynamic levitation furnace. We also investigate the origin of the high refractive index based on the Lines theory. The physical parameters necessary for the theoretical calculations are the averaged nearest-neighbor Ti–O and La–O distances that are deduced by neutron and synchrotron x-ray diffraction measurement and the partial molar volumes of TiO2 and LaO1.5 in the glass. The sum of the calculated TiO2 and LaO1.5 susceptibilities provides a La4Ti9O24 glass refractive index of 2.244. This is very close to the experimental refractive index of the glass. In addition, the theoretical calculation results suggest that the oxygen fivefold Ti (TiO5) cluster produces greater susceptibilities than the sixfold Ti (TiO6) cluster in the glass. [ABSTRACT FROM AUTHOR]

Using a thermodynamic approach based upon the fluctuation-dissipation theorem, we quantify the stochastic dynamics of rectangular and V-shaped microscale cantilevers immersed in a viscous fluid. We show that the stochastic cantilever dynamics as measured by the displacement of the cantilever tip or by the angle of the cantilever tip are different. We trace this difference to contributions from the higher modes of the cantilever. We find that contributions from the higher modes are significant in the dynamics of the cantilever tip angle. For the V-shaped cantilever the resulting flow field is three-dimensional and complex in contrast to what is found for a long and slender rectangular cantilever. Despite this complexity, the stochastic dynamics can be predicted using a two-dimensional model with an appropriately chosen length scale. We also quantify the increased fluid dissipation that results as a V-shaped cantilever is brought near a solid planar boundary. [ABSTRACT FROM AUTHOR]

We have determined a refractive index of an organic single crystal of a thiophene/phenylene co-oligomer in its laser oscillation wavenumbers. We estimated the refractive index to be 4.0 on the basis of the mode intervals of the well-resolved longitudinal multimodes that are highly polarized along the normal to the (001) plane of the single crystal. This large number is in good agreement with that obtained by the quantum chemical calculations at semiempirical levels. This is also consistent with the high Q factor (∼24 500) obtained from the line shape analysis. [ABSTRACT FROM AUTHOR]

Recent experimental data on the dynamics of photoinduced volume changes in chalcogenide glasses are analyzed within a simple phenomenological model. Both kinetics of the volume expansion under continuous irradiation and that of the relaxation after the illumination is switched off are considered. Comparison between theoretical results and experimental data provides a quantitative estimate of the local conversion rate of structural units responsible for the effect into the expanded states. Furthermore, this comparison shows that the conversion rate in a-As2Se3 is several times smaller than that in a-Se. [ABSTRACT FROM AUTHOR]

A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x=0–17.5) alloy system. Low-Pd alloys (x<12.5) reveal low GFA dependence, while high-Pd ones (x>=12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. [ABSTRACT FROM AUTHOR]

The field-dependent hole mobility of 4,4′,4″-tris(1-naphthylphenylamino)triphenylamine (1-NaphDATA) has been measured on hole-only samples with layer thicknesses between 100 and 500 nm. To determine the mobility we employed three different methods: steady-state space-charge limited currents (SCLC), transient dark injection SCL currents (DI-SCLC), and admittance spectroscopy (AS). The results, especially the field dependence of the mobility, depend on the measuring method. The SCLC mobility increases with the layer thickness and becomes constant above 200 nm, which indicates a transition from contact-limited to bulk-limited conduction. Compared to AS and SCLC we found that DI-SCLC is the most reliable method to measure the mobility on thin samples because it is hardly affected by carrier trapping nor by the layer thickness. Using DI-SCLC an organic layer of 200 nm was sufficient to determine the bulk hole mobility of 1-NaphDATA (μ0=6.57×10-6 cm2/V s and γ=2.74×10-3 (cm/V)1/2, which is very thin compared to time-of-flight samples whose thickness is in the range of micrometers. [ABSTRACT FROM AUTHOR]

Ni doping Ti0.5Zr0.25Hf0.25Co1-xNixSb (x=0–0.05) half-Heusler compounds have been fabricated by combining high-frequency induction melting with spark plasma sintering technique, and their thermoelectric transport properties have been investigated in the temperature range of 300–900 K. With the increase of Ni doping content, the electrical conductivity increases significantly, and withal the Seebeck coefficient of all doped samples improve to some extent compared with the undoped Ti0.5Zr0.25Hf0.25CoSb compound. These lead to a great improvement in the power factor, and the highest power factor of 1.63×10-3 W m-1 K-1 is obtained at 715 K for Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb compound. Furthermore, thermal conductivity of Ti0.5Zr0.25Hf0.25Co1-xNixSb compounds decrease remarkably due to Zr and Hf substitutions on Ti site and Ni doping on Co site. Compared with ternary TiCoSb compound, the thermal conductivity of Ti0.5Zr0.25Hf0.25Co1-xNixSb compound decreases 415%–430% at room temperature, and compared with undoped Ti0.5Zr0.25Hf0.25CoSb compound, the thermal conductivity of Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb decreases 34% at 300 K and 21% at 900 K, respectively. A maximum dimensionless figure of merit ZT of 0.51 has been achieved for Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb compound at 813 K. [ABSTRACT FROM AUTHOR]

The performance of magnetic field sensors based upon the giant magnetoimpedance (GMI) effect in soft magnetic wires is investigated in the MHz frequency range. The performance of the sensor is based on its sensitivity, voltage noise level and (voltage) noise-to-sensitivity ratio, or intrinsic magnetic noise level. Optimization of the sensitivity and noise response of the sensor through variation of the sample anisotropy direction and external applied axial field and dc bias current suggest an intrinsic noise level in the [formula] level. Qualitative agreement is obtained between theory and experiment on a CoFeSiB microwire, for the maximum sensitivity and the corresponding noise, as a function of the external field and dc bias current. [ABSTRACT FROM AUTHOR]

Characterization of a vertical cavity surface emitting laser source for a frequency reference that uses coherent population trapping with atomic rubidium is reported. The frequency reference requires a low-noise laser that operates in a single transverse mode at 794.7 nm. We show that biasing the laser at low output power and modulating it at higher frequency than its low relaxation oscillation frequency are necessary to obtain symmetric modulation sidebands and improve the long-term performance of the frequency reference. [ABSTRACT FROM AUTHOR]

The behavior of a microfluidic device based on transport by capillary action and control by direct electrowetting was examined by changing the device parameters. The device was constructed with a polydimethylsiloxane (PDMS) substrate with a flow channel and a glass substrate with electrodes to control electrowetting. The microfluidic transport and valve action could be explained by Washburn’s model, which suggests that the model can be used for designing such a device. The device could be used for the timely delivery of a solution into many flow channels as well as for the mixing of solutions. [ABSTRACT FROM AUTHOR]

A single crystal GaAs wafer with front face mirror polished was irradiated by a 1064 nm continuous laser experimentally. The damage process was investigated by real-time surface reflectivity and optical distribution monitoring. No evident melting and oxidation occurrence was found and the components of Ga and As almost kept constant during the whole damaging process. The distinct differences from the damage by 532 nm continuous laser were analyzed as well. For the current wavelength, the damage threshold was greatly dependent on the boundary conditions, consequently only an estimated threshold value about 2 kW/cm2 was obtained. [ABSTRACT FROM AUTHOR]

The left-handed (LH) behavior of a combined structure of cut wire pair and continuous wire was experimentally studied. It was found that the LH behavior of a combined structure can still be observed as the width of cut wire pair increases until the cut wire joins the continuous wire, the so-called fishnet structure. These structures were designed, fabricated, and measured in the microwave frequency regime. In addition, we report the experimental results of the parametric study on the fishnet structure, which are also compared with the previous theoretical studies. [ABSTRACT FROM AUTHOR]

The dielectric behavior of lithium tantalate (LT) single crystals has been investigated in the vicinity of the ferroelectric phase transition for nonstoichiometric and near-stoichiometric compositions. Fitting of the experimental data to a modified Curie-Weiss equation indicates the occurrence of a mildly relaxor-ferroelectric-like phase transition in congruent LT single crystals (with the Curie-Weiss exponent γ having a value 1.2, rather than the value unity for a regular ferroelectric). As the Li concentration of these crystals approaches the stoichiometric value, the phase transition gets sharper, indicative of an increasing amount of long-range ordering. The bulk concentration of cation vacancies has also been estimated. [ABSTRACT FROM AUTHOR]

We employ a cavity-length study to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269 K with an emission wavelength of 4.05 μm. The characteristic temperature for the gain per unit current density is 39 K, which is slightly lower than T0 of the threshold current and is consistent with dominance by Auger recombination. The internal loss for the 150-μm-wide mesa devices increased from 11 cm-1 at 78 K to 28 cm-1 at 275 K. [ABSTRACT FROM AUTHOR]

The refrigeration processes in the InP/AlInAs triple-well semiconductor system with various structures are analyzed theoretically based on the model of optothermionic refrigeration. Thermal energy extraction in the triple-well system is calculated to be as much as 26 W/cm2 theoretically with properly designed well widths and doping densities. Furthermore, the temperature drop distributions for hot semiconductor devices are obtained self-consistently with various parameters including cross-sectional area, generation heat, environment temperature, and refrigeration heat. [ABSTRACT FROM AUTHOR]

The temperature dependence of the electrical properties of Pt/GaN Schottky barrier was studied. In particular, a Schottky barrier height of 0.96 eV and an ideality factor of 1.16 were found after a postdeposition annealing at 400 °C. Nanoscale electrical characterization was carried out by the conductive biased tip of an atomic force microscope both on the bare GaN surface and on the Pt/GaN contacts. The presence of a lateral inhomogeneity of the Schottky barrier, with a Gaussian distribution of the barrier height values, was demonstrated. Moreover, GaN surface defects were demonstrated to act as local preferential paths for the current conduction. The temperature dependent electrical characteristics of the diodes were discussed in terms of the existing models on inhomogeneous barriers and correlated to the nanoscale electrical characterization of the barrier. In this way, the anomalous electrical behavior of the ideality factor and of the Schottky barrier and the low experimental value of the Richardson’s constant were explained. [ABSTRACT FROM AUTHOR]

The effect of a dc on the interdiffusivity D in the Cu–Ni system was investigated over the temperature range of 650–850 °C and at current densities in the range of 0–1000 A cm-2. Interdiffusivities were calculated using the Sauer–Freise–den Broeder method and the values calculated in the absence of a current were in agreement with previously published results. The influence of the current on D depended on its direction relative to the two interfaces in the trilayered Cu–Ni–Cu samples. When the electronic flow was from Ni to Cu (cocurrent interface), the interdiffusivity showed a marked increase relative to copper content but was unchanged when the electronic flow was from Cu to Ni (countercurrent interface). The increase of D in the cocurrent interface depended on concentration and temperature. At lower temperatures, the increase becomes significant at higher copper concentrations but for the same value of current density, the increase is apparent at lower concentrations. The effective activation energy of interdiffusivity depended on concentration and decreased with the application of a current. The decrease was largest for higher copper concentrations. The results are interpreted in terms of a proposed vacancy-atom interaction for copper with the implication that the electron wind effect on Cu is counteracted by the effect of vacancies. [ABSTRACT FROM AUTHOR]

Improved conductivity has been achieved by controllable substitution of an ultraviolet electronic conductor. The transparent conducting oxide system, H-doped Ca12Al(14-x)SixO(33+x/2) with x=0-4, exhibits a conductivity strongly dependent on the substitution level. Four-point direct current conductivity increases with x from 0.15 to 0.61 S/cm at room temperature. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Si-substituted system with x=0, 2, and 4. Furthermore, the Seebeck coefficient is composition dependent suggesting the existence of an activated mobility associated with small polaron conduction. [ABSTRACT FROM AUTHOR]

Based on the two-step-switching model, the process of electromechanical poling of ferroelectric ceramics is simulated. A difference of the remnant polarizations between two poling protocols (mechanical stress is applied before and after the application of poling field) is found from our simulations, which is also observed in the experiment. An explanation is given to illustrate why the remnant polarization for the case that mechanical stress is loaded after the application of the electric field is larger than the case that mechanical stress is loaded before the application of the electric field. Our simulation results supply proof for the validity of the two-step-switching model in the electromechanical poling of polycrystalline ferroelectric ceramics. [ABSTRACT FROM AUTHOR]

Theoretical calculations have been performed to study the effects of piezoelectric fields in superlattice systems. The results show that cubic strained superlattices and quantum wells subjected to variable temperature and pressure exhibit changes in their piezoelectric fields. We consider superlattice systems grown in arbitrary directions, with a thickness smaller and larger than the critical thickness value (undercritical and overcritical systems). In both cases (including the partially relaxed case), theory predicts the existence of a critical temperature Tm and a critical pressure pm, above which the sign of the piezoelectric fields in each layer reverses. As applications to practical systems, we calculated (1) the piezoelectric fields as a function of temperature in GaAs/ZnSe superlattice and (2) the piezoelectric fields as a function of pressure in GaAs/InAs, GaAs/Si, and ZnSe/GaAs superlattice systems. We present here the results of the effects of piezoelectric fields for three different systems (undercritical systems, overcritical systems, and partially relaxed systems), where the piezoelectric field changes under variable temperature, pressure, and thickness of the layers. We also discuss the valence band offset, which is induced by piezoelectric fields, and its dependence on temperature and pressure. In addition, we present data on the valence band offset for some practical undercritical systems. All results and conclusions are valid in a linear region of strain or stress where no phase transitions occur. [ABSTRACT FROM AUTHOR]

The field enhancement factor of gated nanotube with opened top was analytically calculated by the electrostatic method. The effect of geometrical parameters of the device on their field enhancement factor was investigated, including the gate-hole radius, gate-anode distance, and nanotube radius. The theoretical analysis shows that the enhancement factor increases greatly with the decrease of gate-hole radius. However, if the gate voltage is zero, the factor increases with the increase of gate-hole radius, and finally reaches a constant, which increases with the increase of nanotube length L. The enhancement factor β gets larger when the nanotube radius gets smaller. As the gate-anode distance d2 is finite, the β will decrease with the increase of d2. If the d2 is infinite, the effect of gate-anode distance on β can be ignored. All the results of theoretical calculation can provide useful information in the fabrication and design of the gated nanotube cold cathode for field emission display panels and other nanoscale triode devices. [ABSTRACT FROM AUTHOR]

A discrete formulation of the Wigner distribution function (WDF) and the Wigner transport equation (WTE) is proposed, where the “discreteness” of the WDF and WTE is not just a practical, mathematical feature of discretization for the possible computations, but reveals a fundamental physics regarding the maximum correlation length of potentials (an essential quantum-mechanical feature of the WTE): it is set by the positional uncertainty due to the discrete values of momentum in evaluating the discrete WDF. Our formulation also shows that the weighting function to the potential-correlation term can be derived naturally from a mathematical necessity related to the antiperiodicity of the discrete density operator. In addition, we propose a mutually independent discretization scheme for the diagonal and cross-diagonal coordinates of the density operator, which results in a numerically effective discrete WTE in that it requires much less computational resources without significant loss in accuracy. [ABSTRACT FROM AUTHOR]

We have investigated the photoluminescence (PL) and time-resolved PL from the InN epilayers grown on Si substrates with different buffer layers. The narrowest value of the full width at half maximum of the PL peak is 52 meV with the AlN/AlGaN/GaN triple buffer layer, which is better than previous reports on similar InN epilayers on Si substrates. Based on the emission-energy dependence of the PL decays, the localization energy of carriers is also the least for the InN with a triple buffer layer. According to the x-ray diffraction measurements, we suggest that the reduced lattice mismatch between the InN epilayer and the top buffer layer is responsible for improvement of sample quality using the buffer-layer technique. [ABSTRACT FROM AUTHOR]

(1-x)(K0.42Na0.58)NbO3-xLiSbO3 [(1-x)KNN-xLS] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide method. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.04

In this article we present a quantitative study of the influence of the number and the thickness of the silicon spacer layer on the optical and structural properties of single and multilayers of self-assembled Ge/Si(001) islands. By means of cathodoluminescence spectroscopy, high resolution x-ray diffraction, and transmission electron microscopy, we will show that the island composition and strain status of single-layer samples do not depend on the silicon cap-layer thickness. On the contrary, we found that the strain interaction existing between island layers separated by a silicon spacer layer 33 nm thick (i.e., ∼3 times the mean island height), enhances the SiGe intermixing during the deposition of subsequent layers bringing to a composition inhomogeneity of the intermixed islands of about 18% along the stack. This inhomogeneity is not present in samples having a thicker spacer layer (60 nm) although the strain interaction between different layers is strong enough to drive the island stacking along the vertical direction. We conclude that the latter spacer layer thickness allows us to obtain a highly ordered three-dimensional superlattice of an island having a homogeneous size and composition along the stack itself. [ABSTRACT FROM AUTHOR]

Double-walled carbon nanotubes (DWCNTs) are modeled based on Donnell’s shell theory, and flow-induced instability that is induced when pressure-driven fluid goes through the inner tube at a steady flow velocity is studied. The van der Waals (vdW) interaction between the inner and outer walls is taken into account in the modeling. The numerical simulations show that the vdW interaction has significant effects on the flow-induced instability of DWCNTs. The critical flow velocities and loss of stability are closely related to the ratio of the length to the outer radius. Donnell’s shell model for carbon nanotubes (CNTs) is preferred in simulations because it takes into account the shear effects in the walls. A comparison between the CNTs that are based on a Eulerian beam model and those that are based on Donnell’s shell model shows that when the 50-nm-radius tube length is shorter than 10 μm, the comparative errors between the Eulerian beam and Donnell’s shell models are greatly increased. [ABSTRACT FROM AUTHOR]

A simple nonradiative Shockley-Read-Hall recombination model is used to interpret transient reflectivity and midinfrared transmission experiments of low-temperature-grown GaAs (LT-GaAs) materials annealed under various conditions of temperature and duration. The model introduces two main parameters, namely the deep-donor (NDD) and the acceptor (NA) concentrations in the GaAs matrix, to explain all observed behaviors coherently with other results in the literature. A precise study of the different parameters (pump wavelength and power, NDD, NA, etc.) is performed using our model. The introduction of growth and anneal-related parameters, such as NA and NDD, allows a good understanding of LT-GaAs. These results demonstrate the importance of acceptor densities in the dynamic properties. [ABSTRACT FROM AUTHOR]

This work discusses the temperature-dependent forward current-voltage characteristics of an AlGaInP light-emitting diode. From 300 to 470 K, all curves have the same ideality factor of n=1.58. The temperature-dependent saturation currents are in excellent agreement with the thermal activation behavior over ten decades of current and with an activation energy of Ea=1.405 eV. Based on the discussion of the barrier for forward current flow, nEa corresponds to the band gap of the active layer. Various mechanisms of current flow for pn junctions and Schottky diodes were examined and verified. Therefore, the nEa=2.22 eV of the sample corresponds to the band gap of the barriers in the active layer. This value is consistent with the band gap of (AlxGa1-x)0.5In0.5P for x>0.58. [ABSTRACT FROM AUTHOR]

We show that the polarization of the emission of a single quantum dot embedded within a microcavity pillar of elliptical cross section can be completely controlled and even switched between two orthogonal linear polarizations by changing the coupling of the dot emission with the polarized photonic modes. We also measure the spatial profile of the emission of a series of pillars with different ellipticities and show that the results can be well described by simple theoretical modeling of the modes of an infinite length elliptical cylinder. [ABSTRACT FROM AUTHOR]

During the pulsed-laser microdrilling process using nanosecond pulses, a plasma and a shockwave develop. In order to study their formation and propagation and investigate the possibilities for monitoring the process, we have developed a highly automated experimental setup utilizing two types of detectors: A high-speed beam-deflection probe and a camera equipped with a liquid-crystal light attenuator mounted on an optical microscope. By analyzing the data from both detectors we were able to develop a technique for the online monitoring of hole-depth during the pulsed-laser microdrilling process for glass. It is based on time-of-flight measurements of the shockwave and simultaneous determination of its source size. [ABSTRACT FROM AUTHOR]

The control of the vortex state magnetic nanoparticle by ultrafast magnetic fields is studied theoretically. Using the micromagnetic simulations for the Permalloy nanodisk we demonstrate that the vortex core magnetization can be irreversible switched by the alternating field, rotating in the disk plane, with the frequency about 10 GHz and intensity about 20 mT. We propose an analytical picture of such phenomena involving the creation and annihilation of vortex-antivortex pairs and calculate the phase diagram of the fields parameters leading to the switching. [ABSTRACT FROM AUTHOR]

The introduction of hydrogen chloride (HCl) in the deposition chamber during the growth of 4H-SiC epitaxial layers allows very high growth rates to be achieved. The properties of the epilayers and the growth rate depend on many parameters such as the growth temperature and the C/Si, Cl/Si, and Si/H2 ratios. We have used optical and electrical measurements to investigate the effect of the Cl/Si and Si/H2 ratio and growth temperature on the epitaxial growth process. The growth rate increases with increasing Si/H2 ratio and higher growth rates are obtained when HCl is added to the gas flow. Optical microscopy shows an improvement of the surface morphology, and luminescence measurements reveal a decrease in the concentration of complex defects with increasing Cl/Si ratio in the range of 0.05–2.0 and with increasing growth temperature from 1550 °C to 1650 °C. The electrical measurements on the diodes realized on these epitaxial layers show a decrease of the leakage current with increasing Cl/Si ratio and growth temperature over the same range. Deep level transient spectroscopy measurements indicate that the deep level EH6/7, which is one of the main levels responsible for the high value of leakage current measured in the Schottky diodes, is greatly reduced using HCl as a growth additive. [ABSTRACT FROM AUTHOR]

The crystallographic mechanisms of the crack initiation and propagation in a textured polycrystalline TiNi shape memory alloy were studied using scanning electron microscope and ex situ electron backscattered diffraction techniques. The results indicated that stress-induced martensitic transformation was triggered and formed a sandwich structure at the front of the crack tip prior to the crack initiation in the polycrystalline TiNi alloy. The crack propagated intragranularly and occasionally across the grain boundaries. The closed packed planes of the B2 parent phase such as {110} and {100} were revealed to favor the crack propagation. The stress-induced B2+B19′ sandwich structure determined the crack propagated by a microscopic sawtooth pattern and therefore a ductile feature in this textured polycrystalline TiNi sheet specimen. [ABSTRACT FROM AUTHOR]

We study the Joule heating of a 1.25 μm wide aluminum microstripe excited by an electrical current. The temperature changes are measured with a scanning thermal microscope that uses a small fluorescent particle as a sensor. The lateral resolution observed for this sample is better than 300 nm. We have compared the temperature distribution in the stripe with a simple analytical model of heat propagation in the wire and the substrate. A good qualitative agreement is observed, although the measured temperature is much smaller than the estimated one, showing that the heat transfer between the hot wire and the fluorescent probe is not fully efficient. [ABSTRACT FROM AUTHOR]

Island growth has been shown to also occur for atomic layer deposition (ALD) processes. This article presents a relatively simple analytical model using geometrical principles with few independent variables on evolution of thickness and roughness in island-dominated ALD processes. The model is well suited for the fitting of experimental data to extract parameters such as density of islands and growth rate. It allows islands of various shapes, but most of the attention here is devoted to cone and hemispherical shaped islands in a hexagonal grid on a flat substrate. For a selection of cases, exact analytical expressions are derived. The model shows that it is possible to reproduce the growth characteristics of substrate-inhibited growth of both types 1 and 2 with a suitable choice of functional form of the islands. Finally it is compared with previously advanced models describing substrate-inhibited growth. [ABSTRACT FROM AUTHOR]

Absorption and fluorescence spectra of commercially available polycrystalline ceramic Nd3+:Y2O3 and nanocrystalline aggregates of Nd3+:Y2O3 grown in our laboratory are optically characterized at nominal 8 K and room temperature. In comparing the spectra obtained from these two different sources, we find similarities in terms of the detailed crystal-field splitting of the energy levels of the Nd3+ ion in the Y2O3 host. The 8 K spectra are analyzed for the energy (Stark) level transitions between the 2S+1LJ multiplet manifolds of Nd3+(4f3). The analysis includes the manifolds of 4I9/2 (the ground state), 4I11/2, 4I13/2, 4I15/2, 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4S3/2, and 4F9/2. The results of this study are also compared with a crystal-field splitting analysis reported earlier for single-crystal Nd3+:Y2O3 grown by a modified flame fusion method. We find that the spectroscopic properties of our composites compare favorably with other ceramic and single-crystal forms of Nd3+:Y2O3 currently available. [ABSTRACT FROM AUTHOR]

A high-performance 4H-SiC p-i-n photodetector for visible-blind ultraviolet (UV) applications has been designed and fabricated. The electrical and optical characteristics were measured at room temperature. The photodetector suffered from significant dark current of 2.5 pA/mm2 at reverse bias of 5 V, and the UV light photocurrent was larger than four orders of magnitude higher than the dark current. The built-in potential and the unintentional i-layer doping concentration were obtained from capacitance-voltage (C-V) measurements. The spectral peak responsivity of the detector reached 0.13 A/W at a wavelength of 270 nm, corresponding to a maximum external quantum efficiency of ∼61%. And the ratio of responsivity at 270 nm to that at 380 nm was >103. The characteristics imply that the photodetector has a great improved ultraviolet-visible rejection ratio which is needed for ultraviolet signal detection. [ABSTRACT FROM AUTHOR]

A wave propagation model in macroscopically inhomogeneous porous media is derived from the alternative Biot’s theory of 1962. As a first application, the wave equation is reduced and solved in the case of rigid frame inhomogeneous porous materials. The pressure field, as well as the reflection and transmission coefficients, are obtained numerically using a wave splitting and “transmission” Green’s functions approach (WS-TGF). To validate both the wave equation and the method of resolution at normal and oblique incidence, results obtained by the WS-TGF method are compared to those calculated by the classical transfer matrix method and to experimental measurements for a known two-layered porous material, considered as a single inhomogeneous layer. Discussions are then given of the reflection and transmission coefficients for various inhomogeneity profiles as well as of the internal pressure field. [ABSTRACT FROM AUTHOR]

We characterized the current-voltage, voltage-flux, and the field sensitivity of integrated high-Tc series superconducting quantum interference device (SQUID) magnetometers and gradiometers. The series two-SQUID magnetometers shows field sensitivities of ∼30–40 fT/Hz1/2 at 1 kHz and ∼80–100 fT/Hz1/2 at 1 Hz over that of a one-SQUID magnetometer in shielded environment. The field sensitivity of a series two-SQUID gradiometers is ∼60 fT/Hz1/2 cm, while the one-SQUID gradiometer shows a gradient sensitivity of ∼80–150 fT/Hz1/2 cm at 1 kHz in an unshielded laboratory environment. The series two-SQUID magnetometers or gradiometers show a significant improvement in flux noises over that of one-SQUID magnetometers or gradiometers. [ABSTRACT FROM AUTHOR]

First principles calculations of mechanical properties of the YVO4 single crystal have been carried out after geometry optimization. We demonstrate that using first principles calculations is a simple and fast method for determining mechanical properties from crystals. The calculated elastic stiffness constants Cij are in good agreement with previous experimental data recorded in the literature. Our results also indicate that the anisotropic property of elastic stiffness constants is due to its lattice structure and electron-charge density distribution. The material constant Ms is also discussed in this work. [ABSTRACT FROM AUTHOR]

As-rich and Ga-rich GaAs(001) surfaces were studied with frequency-modulation dynamic force microscopy. By simply changing the parameters of argon sputtering and annealing during sample preparation, surfaces reconstructed with the As-rich c(4×4) phase or the Ga-rich c(8×2) phase could be obtained. True atomic resolution of the c(8×2) reconstruction is achieved by using constant frequency shift imaging. We show that tip functionalization allows selective species imaging. The presence at the tip apex of empty Ga dangling bonds or of fully filled As dangling bonds leads to selective atomic resolution of the As or Ga sublattices of the c(8×2) reconstructed surface, respectively. Our observations support the ζ model for the c(8×2) reconstruction (but no dimers were found) and the α model for the c(8×2) reconstruction (individual As–As dimers were resolved by dynamic force microscopy). [ABSTRACT FROM AUTHOR]

c-plane oriented GaN nucleation layers have been grown on (100) γ-LiAlO2 substrates by hydride vapor phase epitaxy. Longer recrystallization time favors the decomposition of the LiAlO2 substrate underneath the layers. The LiAlO2 decomposition at the GaN/LiAlO2 interface is accompanied by the formation of the epitaxial LiAl5O8 crystallites which are at least partly surrounded by cavities in the LiAlO2 matrix. The results suggest a mechanism that explains the spontaneous separation of thick GaN layers from LiAlO2 substrates during post-growth cooling down. [ABSTRACT FROM AUTHOR]

Recent experiments indicate that Sm–Fe melt-spun ribbons with the Sm5Fe17 phase exhibit high coercivity. To elucidate this phenomenon, we performed magnetization measurements and microstructural studies of Sm5Fe17 melt-spun ribbon with coercivity. We found that the coercivity of Sm5Fe17 melt-spun ribbon is single-domain type, and that Sm5Fe17 melt-spun ribbon with high coercivity possesses fine grains of 10–20 nm in diameter. [ABSTRACT FROM AUTHOR]

c-plane oriented GaN nucleation layers have been grown on (100) γ-LiAlO2 substrates by hydride vapor phase epitaxy. Longer recrystallization time favors the decomposition of the LiAlO2 substrate underneath the layers. The LiAlO2 decomposition at the GaN/LiAlO2 interface is accompanied by the formation of the epitaxial LiAl5O8 crystallites which are at least partly surrounded by cavities in the LiAlO2 matrix. The results suggest a mechanism that explains the spontaneous separation of thick GaN layers from LiAlO2 substrates during post-growth cooling down. [ABSTRACT FROM AUTHOR]

In this work we show that a reparametrized Tersoff potential accurately reproduces the bond length variations observed in ternary Ga1-xInxAs mixed crystals. The reparametrization is based on accurate first-principles electronic structure calculations. Previous parametrizations of the Tersoff potential for GaAs and InAs structures, although they accurately reproduce the properties of the zinc-blende GaAs and InAs crystals, are shown to be unable to reproduce the bond length variations in these mixed crystals. In addition to correcting the bond length inconsistencies, the new set of parameters is also shown to yield the elastic constants of GaAs and InAs that agree fairly well with measurements and to reproduce accurately their respective melting temperature. [ABSTRACT FROM AUTHOR]

The temperature, current, and magnetic field dependences of the transport properties at the interface between La0.8Ca0.2MnO3 and Nb(0.1%):SrTiO3 were studied. The striking feature in the present transport data is the appearance of a charging effect that typically occurs in RC circuits. It can be well modeled by a simple RC equivalent circuit. The results show that the interface of the present junctions has a very large capacitance with a value of the areal capacitance of 60 nF/mm2 leading to a very large time constant of the order of 100 s at 100 K. Both the interfacial resistance and the time constant significantly decrease with increasing temperature, current, and magnetic field, whereas the interfacial capacitance remains essentially unchanged. This phenomenon opens up the possibility for the development of a different type of current, magnetic field, and temperature sensitive capacitor. [ABSTRACT FROM AUTHOR]

In this article, to realize precise control of gas phase and surface reactions for high rate synthesis of high quality microcrystalline silicon (μc-Si) films, influences of source gas supply method and direct current (dc) substrate bias during film deposition process are investigated utilizing a microwave plasma source. It is found that the supply of SiH4 source gas near the substrate holder significantly enhances the deposition rate and mass density of deposited film and reduces film defect density while maintaining high crystallinity. On the other hand, a negative dc substrate bias induces film crystallization from the initial growth stage. An appropriate negative dc bias also leads to higher film cystallinity and density. Kinetics of the controlling gas phase and surface reactions through the optimizing source gas supply method and dc substrate bias is demonstrated. We claim that the high flux film precursor SiH3 and H along with less contribution of short-lifetime radicals on the film growing surface and ion-assist structural relaxation benefit the high-rate synthesis of high quality μc-Si films. [ABSTRACT FROM AUTHOR]

In this paper, the temporal evolution of the ion-matrix sheath near a target with a rectangular groove as a function of time and potential is investigated numerically. A two-dimensional model with a single groove is adopted. The profiles of potential, ion density, and the normalized ion flux over the sidewall and the floor of the groove are obtained. These profiles are provided for insight regarding the uniformity and efficiency of ion implantation on the sidewall. [ABSTRACT FROM AUTHOR]