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Molecular dynamics (MD) simulations were performed on model interfaces between n -hexane and water and between water and 1-hexanol. The SPC/E model was used for water. Organic molecules were modeled with united atom potentials located at heavy nuclei, but included explicit modeling of the alcohol H. The structure of the interface was examined in terms of its position, thickness, roughness, and molecular orientations. Additionally, self diffusion coefficients in each phase and the interfacial tension were determined. Significant differences in the interfacial structure were found between the immiscible and partially miscible systems. The interface for the immiscible system is molecularly sharp with only small dynamic waves or corrugation. On the other hand, the interface in the partially miscible system consists of a molecularly sharp region and a bilayer of hexanol oriented with the OH heads out. Relatively static waves corrugate the inner part of the interface considerably more than that for the immiscible system. Water solubility in the hexanol phase occurs in hydrogen bonded cages formed by the OH groups of the alcohol. [ABSTRACT FROM AUTHOR]

The impact of interfacial dynamics on turbulent heat transfer at a deformable, sheared gas-liquid interface is studied using Direct Numerical Simulation (DNS). The flow system comprises a gas and a liquid phase flowing in opposite directions. The governing equations for the two fluids are alternately solved in separate domains and then coupled at the interface by imposing continuity of velocity and stress. The deformations of the interface fall in the range of capillary waves of waveslope ak=0.01 (wave amplitude a times wavenumber k), and very small phase speed-to-friction velocity ratio, c/u[sub*]. The influence of low-to-moderate molecular Prandtl numbers (Pr) on the transport in the immediate vicinity of the interface is examined for the gas phase, and results are compared to existing wall-bounded flow data. The shear-based Reynolds number Re[sub*] is 171 and Prandtl numbers of 1, 5, and 10 were studied. The effects induced by changes in Pr in both wall-bounded flow and over a gas-liquid interface were analyzed by comparing the relevant statistical flow properties, including the budgets for the temperature variance and the turbulent heat fluxes. Overall, Pr was found to affect the results in very much the same way as in most of the available wall flow data. The intensity of the averaged normal heat flux at high Prandtl numbers is found to be slightly greater near the interface than at the wall. Similar to what is observed in wall flows, for Pr=1 the turbulent viscosity and diffusivity are found to asymptote with z&sup+3;, where z[sup+] is the distance to the interface, and with z[sup+n], where n>3 for Pr=5 and 10. This implies that the gas phase perceives deformable interfaces as impermeable walls for small amplitude waves with wavelengths much larger than the diffusive sublayers. Moreover, high-frequency fluctuating fields are shown to play a minor role in transferring heat across the interface, with a marked filtering effect of Pr. A new scaling law for... [ABSTRACT FROM AUTHOR]

Two- and three-dimensional numerical simulations are performed to study interfacial waves in a periodic domain by imposing a source term in the horizontal momentum equation. Removing the source term before breaking generates a stable interfacial wave. Continued forcing results in a two-dimensional shear instability for waves with thinner interfaces, and a convective instability for waves with thick interfaces. The subsequent three-dimensional dynamics and mixing is dominated by secondary cross-stream convective rolls which account for roughly half of the total dissipation of wave energy. Dissipation and mixing are maximized when the interface thickness is roughly the same size as the amplitude of the wave, while the mixing efficiency is a weak function of the interface thickness. The maximum instantaneous mixing efficiency is found to be $0.36\pm 0.02$. [ABSTRACT FROM AUTHOR]

A diffuse-interface method is proposed for the simulation of interfaces between compressible fluids with general equations of state, including tabulated laws. The interface is allowed to diffuse on a small number of computational cells and a mixture model is given for this transition region. We write conservation equations for the mass of each fluid and for the total momentum and energy of the mixture and an advection equation for the volume fraction of one of the two fluids. The model needs an additional closure law. We study two different closure laws: isobaric and isothermal. We study the mathematical properties of the resulting models: consistency, hyperbolicity, and existence of a mathematical entropy. We also study the stability of the interfaces with respect to averaging due to the numerical diffusion, a crucial property for the simulation of interface problems by conservative schemes. We show that the isobaric closure is preferable to the isothermal closure with respect to this property. We propose a Roe-type numerical scheme for the simulation of the model and show numerical results for classical test cases. [Copyright &y& Elsevier]

The use of micromechanically based constitutive equations for contact interfaces leads to technically relevant parameters to ill-conditioned finite-element equations. In the paper an augmented Lagrangian technique is employed to overcome this difficulty and to provide a good converging algorithm. [ABSTRACT FROM AUTHOR]

The method of measuring position/orientation in the real world determines the construction of the VR interface. This paper proposes a method of measuring marker position/orientation by image processing. The marker is rectangular. The position/orientation is measured using a single camera. The orientation of the marker is estimated by optimization, utilizing the information of two vanishing points obtained from an image. Then, the position of the marker is determined by calculations. This is facilitated because we have only to attach a marker to a target of measurements. The expansion in the measurement of multiple objects is straightforward and the system can be constructed cheaply because no special circuitry is required. Also, the measurement range is easily modified by resetting the camera lens. The advantage of this method is shown by computer simulations and experimental results using a real image. The real-time measuring accuracy of the system, which was composed of ready-made devices and a highly distorted camera, was 0.5 degrees in directional deviations and 1 mm in depth deviation. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(3): 1–12, 1997 [ABSTRACT FROM AUTHOR]

Inductive response of supercapacitor to switching of charging current has been examined. The observed effect has been interpreted as a consequence of mechanical inertia of liquid conducting system (electrolyte). The proposed interpretation has been confirmed by simulation experiment. [ABSTRACT FROM AUTHOR]

Abstract: This letter presents a study on the influence of the three different etching modes (isotropic, anisotropic and sputtering) on the dynamics of smoothing of roughed surfaces. Calculations were performed using a three-dimensional simulation package based on the level set method. The obtained simulation results clearly show that the surface roughness could be reduced by both the sputtering and the isotropic etching, although the sputtering process is much more efficient. On the other hand, it is shown that the anisotropic etching is not an effective mechanism of smoothing. The time dependence of the interface width is analyzed and growth exponent β has been determined for all etching modes. [Copyright &y& Elsevier]

Abstract: The drift length Ldrift = μτE within the i layer of a-Si:H solar cells is a crucial parameter for charge collection and efficiency. It is strongly reduced not only by light-induced reduction of μτ, but also by electric field deformation ΔE by charges near the p–i and i–n interfaces. Here, a simple model is presented to estimate contributions of free carriers, charges trapped in band tails and charged dangling bonds to ΔE. It is shown that the model reproduces correctly trends observed experimentally and by ASA simulations: charged dangling bonds contribute most to ΔE of meta-stable cells. Electrons trapped in the conduction band tail near the i–n interface lead to the strongest field deformation in the initial state, while positively charged dangling bonds near the p–i interface get more important with degradation under AM1.5g spectrum. The measurable parameter V coll is proposed as an indirect parameter to estimate the electric field, and an experimental technique is presented that could enable the distinction of defects near the p–i and the i–n interfaces. [Copyright &y& Elsevier]

The translocation of a polymer through compound channels under external electrical field was investigated by Monte Carlo simulation on a three-dimensional simple cubic lattice. The compound channel is composed of two parts: part α with length Lpα and part β with length Lpβ. The two parts have different polymer-channel interactions: a strong attractive interaction with strength &eh;α for part α and a variable interaction with strength &eh;β for part β. Results show that the translocation process is remarkably affected by both &eh;β and Lpα, and the fastest translocation can be achieved with a proper choice of &eh;β and Lpα. When &eh;β is large, the translocation is dominated by the last escaping process as it is difficult for the polymer chain to leave the channel. Whereas when Lpα is small and &eh;β < &eh;α, the translocation is determined by the initial filling process. For this case, there is a free-energy well at the interface between the part α and the part β, which not only influences the filling dynamics but also affects the translocation probability. [ABSTRACT FROM AUTHOR]

The analysis of injection-dependent charge carrier lifetimes is a well-established method to determine material and interface quality in crystalline silicon wafer-based device structures such as solar cells. However, for thin films, this method has rarely been used. One reason is that the physical interpretation of experimental data must rely on advanced theoretical models. In this study, we show by numerical simulations and analytical approximations that the effective charge carrier lifetime in thin films is heavily affected by space charge regions (SCR) over a wide range of injection levels. By analysis of the characteristic features in the injection-dependent effective charge carrier lifetime curves, qualitative information about SCRs that occur at grain boundaries or interfaces can be obtained. In contrast, information about the defect density can only be extracted in a very limited range of injection levels and the relationship between effective charge carrier lifetime and the quasi-Fermi level splitting, which is limiting the open circuit voltage of wafer-based solar cells, is not valid in thin films. On the basis of this theoretical study, we analyze measurements of effective charge carrier lifetime in 1.5 μm thin and 2 μm fine-grained polycrystalline silicon films with lifetimes of up to 100 μs and find experimental evidence for grain boundary potential barriers. Finally, we present guidelines for optimized photoconductance measurements and the evaluation of charge carrier lifetimes in thin films, in general. [ABSTRACT FROM AUTHOR]

Resonant tunneling features through impurity clusters embedded in an insulating matrix have been examined through the inter-play between the size of the clusters and the inter-cluster distance. Constructive interference phenomena were tuned through a systematic study of different geometrical configurations, thereby controlling confinement in quasi-bound states. Gaussian trap potentials have been used to simulate the imperfect barrier-well interface associated with disordered materials. Strongly localized states can be formed successfully despite weak disorder as illustrated by breaking the symmetry in the horizontal configuration. To this end, triangular cluster configurations were investigated under a variety of conditions including various shapes and orientations. The effects of disorder created effectively by the arbitary configurations destroy the Fano resonance, which is previlent in conductance spectra and consequently reduce the peak to valley ratio of the resonant peak in current vs. voltage curves. However the formation of two quasi-bound states is demonstrated, suggesting possible applications for disordered naturally grown systems of impurity clusters. This work addresses the controlled lifetime of quasi-bound states and can inform the design of fast switching devices based on high band gap materials by the astute incorporation of impurity clusters with specific geometrical configurations. [ABSTRACT FROM AUTHOR]

Abstract: Two surface plasmon resonance dips in reflectance angular spectrum for a p-polarized incident beam of a [prism/Ag/SiO2 helical thin film] Kretschmann configuration are measured and compared with simulations. The simulation also shows that the angular positions of resonances due to surface plasmon waves in reflectance spectrum are sensitive to the variation of principal refractive indices of helical films. It indicates that multiple surface plasmon waves at the [Ag/SiO2 helical thin film] interface is more attractive than the traditional method of producing only one surface plasmon wave for chemical- and bio-sensing applications. [Copyright &y& Elsevier]

Molecular modeling simulations reveal the role of stereogenic centers in the formation of enantiomorphoussurface-confined supramolecular rosette-like assemblies in monolayers of oligophenylene vinylene oligomers adsorbed at the graphite/solvent interface. [ABSTRACT FROM AUTHOR]

Making good electrical contacts to nanodevice channels is crucial for device performance. Carbon-based nanomaterials are studied and compared to each other as the contact materials for graphene nanoribbons (GNRs) by atomistic quantum transport simulations. A monolayer graphene that has an AB stacking structure on the GNR offers the best electrical contact. Rotation of the graphene layer with regard to the GNR leads to a considerable increase in the contact resistance and contact transfer length. Importance of wave vector matching and interfacial defects is examined for improving electrical contacts to GNRs. This paper could be useful for designing all-carbon-based circuits. [ABSTRACT FROM AUTHOR]

Abstract: A generally available and easy-to-use viewer for the simultaneous visualisation of the ASDEX Upgrade vacuum vessel computer aided design models, diagnostics and magnetic geometry, solutions of 3D plasma simulation codes and 2D camera images was developed. Here we report on the working principle of this software and give several examples of its technical and scientific application. [ABSTRACT FROM AUTHOR]

Abstract: Advanced nuclear fuel concepts sometimes involve metal oxide interfaces between fissile and nonfissile phases. During operation, cascade damage as secondary events from a fission track will occur throughout the material. Some of that damage will take place at the interface between phases. Here we simulate representative secondary events of this nature. As a model system, ongoing experiments consider a composite in which the nonfissile material is magnesia and the fissile phase is modeled via hafnia as a surrogate. In correspondence the experiments, the atomistic simulation cells are composed of hafnia in the fluorite structure and magnesia in the rocksalt structure. Molecular dynamics simulations of cascade damage across interfaces of these materials shows Hf cations becoming kinetically trapped in the magnesia phase. The Hf cations remained trapped for the duration of the 20-ps simulations. When the primary-knock-on atom energy is above a few hundred eV in the direction of the interface and is within five lattice spacings, the propensity for trapping is very high. Under these same conditions, an Mg cation will occasionally become trapped in the hafnia. Complementary electronic structure calculations indicate that Hf cations are thermodynamically unstable in magnesia. Furthermore, these calculations indicate that the charge on the Hf ions reduces by one electron if no compensating defect is present, but reverts to the charge in HfO2 bulk in the presence of a defect such as an oxygen interstitial. Extensions of these observations to the behavior of urania and ceria are mentioned. [ABSTRACT FROM AUTHOR]

Abstract: In glass–ceramics, the density difference between the new, semi-crystalline system, and the ambient phase requires a deformation of the grains. However, the first stage of surface induced crystallization is the creation of rigid shell, opposing the shrinkage. Therefore, an important stress appears inside the grain. If the average density of the new system is higher than that of the ambient phase, a tensile stress is generated. In the opposite case, a compressive stress is developed. As soon as the system is neither pure elastic body nor pure plastic one, the concentration of the stress energy depends on the distance from the interface. We describe theoretically the distribution profile of the stress energy. Depending on the stress attenuation parameter and the grain size, there are two solutions. The first one predicts a maximum in the middle of the grain. According to the second, there are two maxima close to the crystal/glass interface. This explains the appearance of cabbage like crystals or of crystalline grains with a pore in the center. [Copyright &y& Elsevier]

We present a generalized model of the density of interface states at III-V oxide interfaces. The states are based on the native defects such as dangling bonds on the Ga and As sites or As–As bonds created by oxidation. The model explains the difficulty of n-type operation for GaAs field effect transistors (FETs) compared to GaAs pFETs or to InGaAs nFETs. [ABSTRACT FROM AUTHOR]

Thermal conduction governs the writing time and energy of phase-change memory (PCM) devices. Recent measurements demonstrated large thermal resistances at the interfaces of phase-change materials with neighboring electrode and passivation materials. In this letter, electrothermal simulations quantify the impact of these resistances on the set to reset transition. The programming current decreases strongly with increasing boundary resistance due to increased lateral temperature uniformity, which cannot be captured using a reduced effective conductivity in the phase-change material. Reductions in programming current from 20% to 30% occur for an interface resistance of 50 m[sup2] . K/GW. The precise spatial distribution of thermal proper- ties is critical for the simulation of PCM devices. [ABSTRACT FROM AUTHOR]

The interface capacitance model is briefly revised. It is emphasized that this is a device model related to the boundary condition for polarization and unable to explain the thickness evolution of the ferroelectric properties. The model can be applied to extract the properties of the film from those measured in the capacitor. The interface parameters are found to be temperature independent. The coupling of the film with the interface and the electrode is shown to result in the measured frequency dependent permittivity totally different from that of the film. [ABSTRACT FROM AUTHOR]

As a growing importance is placed on developing more efficient organic solar cells, understanding the behavior of free charge carriers at the metal/organic (M/O) interface is critical. One of the current challenges is understanding surface losses, essentially the loss of free charge carriers at the electrode/organic interface. In this paper, we use device model simulations to study such phenomena and we pay particular attention to the role of polaron pair (PP) M/O interfacial dissociation. The origin of surface losses is through the extraction of free charge carriers from the wrong electrodes, or direct surface recombination of PPs. Through simulation, we find that a high injection barrier leads to a large surface loss. In addition, surface loss increases with both the interfacial dissociation rate and PP diffusivity. Efficient interfacial dissociation can significantly enhance surface losses if the PP diffusivity is relatively large. Furthermore, current voltage characteristics reveal that surface losses undermine the device operating parameters and efficiency. Interlayers inserted at the M/O interface could block wrong electrode carriers, suppress the interfacial dissociation and reduce surface losses. [ABSTRACT FROM AUTHOR]

We have used molecular dynamics simulations to calculate the interfacial tension of hydroxylated SiO2 nanoparticles under different temperatures and solutions (helium and brine with monovalent and divalent salts). In order to benchmark the atomistic model, quartz SiO2 interfacial tension was measured based on inverse gas chromatography under He atmosphere. The experimental interfacial tension values for quartz were found between 0.512 and 0.617 N/m. Our calculated results for the interfacial tension of silica nanoparticles within helium atmosphere was 0.676 N/m, which is higher than the value found for the system containing He/α-quartz (0.478 N/m), but it is similar to the one found for amorphous silica surface. We have also studied the interfacial tension of the nanoparticles in electrolyte aqueous solution for different types and salts concentrations (NaCl, CaCl2, and MgCl2). Our calculations indicate that adsorption properties and salt solutions greatly influence the interfacial tension in an order of CaCl2 > MgCl2 > NaCl. This effect is due to the difference in distribution of ions in solution, which modifies the hydration and electrostatic potential of those ions near the nanoparticle. [ABSTRACT FROM AUTHOR]

The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte Carlo simulations at densities inside the two-phase coexistence region of fluid and solid. Choosing a geometry where the system is confined between two flat walls, and a wall-colloid potential that leads to incomplete wetting of the crystal at the wall, conditions can be created where a single nanoscopic wall-attached crystalline cluster coexists with fluid in the remainder of the simulation box. Following related ideas that have been useful to study heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we estimate the contact angles from observations of the crystalline clusters in thermal equilibrium. We find fair agreement with a prediction based on Young's equation, using estimates of interface and wall tension from the study of flat surfaces. It is shown that the pressure versus density curve of the finite system exhibits a loop, but the pressure maximum signifies the 'droplet evaporation-condensation' transition and thus has nothing in common with a van der Waals-like loop. Preparing systems where the packing fraction is deep inside the two-phase coexistence region, the system spontaneously forms a 'slab state,' with two wall-attached crystalline domains separated by (flat) interfaces from liquid in full equilibrium with the crystal in between; analysis of such states allows a precise estimation of the bulk equilibrium properties at phase coexistence. [ABSTRACT FROM AUTHOR]

Monte Carlo and molecular dynamics computer simulations have been used to study the structure and dynamics of the interlayer aqueous solution in a colloidal sodium laponite clay at 277 K. The system studied has a clay-clay spacing of 34.06 Å, and contains 1200 interlayer water molecules and 24 sodium counterions. The density profiles for interlayer species show two distinct layers of surface water as one moves away from the clay particles. The innermost of these layers is strongly oriented to form hydrogen bonds to the surface oxygen atoms. Radially averaged pair distributions have been calculated as a function of distance from the clay surfaces, and show that throughout our system the water structure is significantly perturbed from the bulk. In particular, we observe an increase in the second nearest-neighbor oxygen-oxygen distance, similar to that reported for low-density water at 268 K [A. K. Soper and M. A. Ricci, Phys. Rev. Lett. 84, 2881 (2000)]. The majority of the sodium counterions are fully hydrated by six water molecules. These hydrated ions have a strong tendency to remain close to the solid surfaces, as so-called "outer-sphere" complexes. However, we also observe cations further from the clay sheets, in the diffuse layer. Diffusion of water and cations in the plane of the clay sheets is comparable to that in the bulk, but is significantly reduced normal to the clay sheets. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

For the first time, we have explored the effect of positive and negative interface trap charges on the dopingless device using charge plasma concept and named the proposed device as heterogeneous gate dielectric charge plasma tunnel field-effect transistor (HD-CP-TFET). The heterogeneous gate dielectric is considered to improve the ON-state current and device performance. The main intention of this work is to improve the drain current, transconductance characteristics along with linearity figure-of-merits (FOMs). A comparative analysis is done with conventional CP-TFET in the presence of interface trap charges (ITCs). From comparative results, it is found that the proposed device shows a better performance in the presence of interface trap charges. All the simulations are performed on ATLAS TCAD device simulator. The results show that the proposed device has a better tunneling current, transconductance (gm), cut-off frequency (fT), second-order voltage intercept point (VIP2), third-order voltage intercept point (VIP3), third-order input intercept point (IIP3), and third-order intermodulation distortion (IMD3). Thus, the proposed device (HD-CP-TFET) shows the better performance in the presence of interface trap charges and indicates that this device is suitable for low-voltage analog/RF applications. [ABSTRACT FROM AUTHOR]

There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account. [ABSTRACT FROM AUTHOR]

Water-saturated porous media often exhibit a seismoelectric effect due to the existence of an electrical double layer and a relative flow of pore fluid. Here we consider the seismoelectric waves in an open borehole surrounded by water-saturated porous formation which exhibits discontinuity of electrochemical properties at a cylindrical interface. We carefully analyze the seismoelectric interface response since these signals show sensitivity to contrasts in electrochemical properties across an interface. Both coupled and approximate methods are used to compute borehole seismoelectric fields. The simulation results show that the radiated electromagnetic wave from the electrochemical interface is generated due to the change of salinity in pore fluid in the porous formation. However, the elastic properties of the formation remain unchanged across such an electrochemical interface. As a result it is difficult to recognize such a change in electrochemical properties using only elastic waves. Therefore, the seismoelectric interface response is potentially used to detect the changes of the electrochemical properties in the formation. [ABSTRACT FROM AUTHOR]

The article discusses the simulation of multifunctional structures and offers a look into how more powerful computers and better algorithms are making it possible to probe and engineer the properties of nanostructures at their atomic-level. Developments in materials simulation, which are driven by advances in algorithms, are leading interfacial engineering designs and nanostructures with prescribed properties. According to the authors, the missing piece to such device-size simulations are descriptions of interatomic interactions that allow differently bonding materials to be treated in an integrated manner. Topics include an in-depth look at the various interfaces between disparate bonding environments such, as metallic and microelectronics, and the challenges to their application.