Boundary treatment effects on molecular dynamics simulations of interface thermal resistance

Molecular Dynamics simulations of heat conduction in liquid Argon confined in Silver nano-channels are performed subject to three different thermal conditions. Particularly, different surface temperatures are imposed on Silver domains using a thermostat in all and limited number of solid layers, resulting in heat flux in the liquid domain. Alternatively, energy is injected and extracted from solid layers to create a NVE liquid Argon system, which corresponds to heat flux specification. Imposition of a constant temperature region in the solid domain results in an unphysical temperature jump, indicating the presence of an artificial thermal resistance induced by the thermostat. Thermal resistance analyses for the components of each case are performed to distinguish the artificial and interface thermal resistance effects. Constant wall temperature simulations are shown to exhibit superposition of the artificial and interface thermal resistance values at the liquid/solid interface, while applying thermostat on wall layers sufficiently away from the liquid/solid interface results in consistent predictions of the interface thermal resistance. Injecting and extracting energy from each solid layer eliminates the artificial resistance. However, the method cannot directly specify a desired temperature difference between the two solid domains.     

Boundary conditions at a fluid-solid interface

We study the boundary conditions at a fluid-solid interface using molecular dynamics simulations covering a broad range of fluid-solid interactions and fluid densities and both simple and chain-molecule fluids. The slip length is shown to be independent of the type of flow, but rather is related to the fluid organization near the solid, as governed by the fluid-solid molecular interactions.     

Transport properties of the interface metal chalcogenide/vacuum

The process of spontaneous thermal dissociation of the semiconducting nonstoichiometric compounds Cu_2-δX (X=S, Se) in vacuum has been investigated. Thermogravimetric, X-ray and electrochemical techniques reveal that the dissociation rates sharply decrease at δ≤δ_cr. (δ_cr.=f(T)) and the chalcogen fluxes from the compounds into the vacuum become immeasurably small. The results of the experiments are discussed in terms of the formation of a phase at the surface with properties of a compound of constant composition. Possible reasons are the excess surface energy together with the high mobility of copper ions which results probably in the reconstruction of the subsurface layers.     

Hydrogen plasma modification of metal/GaAs interface

GaAs surface modification caused by room-temperature atomic hydrogen treatment in an RF plasma system operated in the reactive ion etching (RIE) mode has been studied by electrical characterization of subsequently fabricated Au/GaAs Schottky barriers. Unlike with reported results for plasma hydrogenation at higher temperatures, the Schottky barrier height on n-GaAs is found to decrease slightly. More interestingly, a pronounced increase in the effective barrier height is seen for p-GaAs. Dopant deactivation close to the surface is also observed for both conductivity types.     

Boundary conditions for an electromagnetic field in the presence of a rough interface

Kharkov State University. Translated from Izvestiya Vysshikh Uchebykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1091–1096, September, 1989.     

Surface resistance measurements at the metal/electrolyte interface of Ag(100) and Ag(111) thin film electrodes

The conductivity of thin film metal electrodes with a thickness of the order of the mean free path of the conduction electrons (50 nm at 300 K) is sensitive to several processes on the metal surface (e.g. adsorption and desorption of ions). We developed epitaxially grown Ag(100)/MgO(100) and Ag(111)/TiO₂(110) electrodes of 20 nm thickness. The change in the surface resistance of Ag(100) thin film electrodes during adsorption of the halide ions Cl⁻, Br⁻ and I⁻ shows the different strengths of specific adsorption. We investigated the phase transition of thiocyanate (SCN⁻) on Ag(100) electrodes by combining the surface resistance method with voltammetric, capacitance and ex-situ XPS measurements. The influence of adsorbed uracil on the resistance of Ag(100) films was demonstrated. The surface resistance is very sensitive to small concentrations of metal cations (e.g. Tl⁺). The surface resistance of Ag(100) and Ag(111) thin film electrodes shows the typical difference in the stripping potential of Tl⁺ of about 100 mV.     

螺旋线慢波结构中界面热阻率的研究

通过理论和实验的方法,对螺旋线慢波结构中的界面热阻率进行了研究.分析了两个接触处的界面热阻率对慢波结构散热性能的不同影响.提出了一种计算界面热阻率的方法,并对其准确性和可行性进行了验证.该方法可以分别估算两个接触处的界面热阻率,并考虑了组件材料属性随温度变化的特性.利用该方法研究了夹持杆材料和装配方法对螺旋线慢波结构界面热阻率的影响. 关键词： 慢波结构 散热性能 界面热阻率     

Surface and interface dipoles on catalytic metal films

The work function changes introduced by hydrogen on the surface and at the metal-support interface of a thin Pd-film were studied by simultaneous Kelvin probe and C(V)-measurements. It is demonstrated how these techniques can be used at atmospheric pressures to yield information about catalytic metals and on chemical kinetics on the metal surface. The main purpose of the communication is to point out the correlation between the surface and interface dipoles on catalytic metal films. Furthermore since the interface dipole is only created by hydrogen atoms it is shown how this can be used in a more complex situation to independently monitor the hydrogen content of the metal films.     

Electrically tunable resistance of a metal

Electric field-induced tuning of material properties is usually restricted to nonmetals such as semiconductors and piezoelectric ceramics. We show that variations of the electrical resistance of a metal (Pt) in the range of several percent can be reversibly induced at low charging voltages making use of a nanocrystallite-electrolyte composite. The charge-induced resistance variation is analyzed taking into account the modification of the charge carrier density and scattering rate by surface charging. The contribution arising from the charge-induced variation of the lattice constant is found to be small.     

Influence of parameters of the potential barrier at the metal/polymer interface on the electronic switching in the metal/polymer/metal structure

The influence of the first-order phase transition on the parameters of the potential barrier at the indium/polymer interface has been investigated. It has been established that the phase transition occurring in the metal initiates switching of the polymer insulator into a high-conductivity state. Performed investigations have shown that the main charge transfer mechanism in the metal-polymer-metal structure at high temperatures is the current caused by the electron thermionic emission. The analysis of current-voltage characteristics has demonstrated that the first-order phase transition in indium leads to the variation in the potential barrier height at the metal/polymer interface by Δφ ≈ 0.18 eV. It is this phenomenon that is responsible for the electronic switching.     

Thermoelectric effects in normal metal/superconductor interface structures

The thermopower of Andreev interferometers, which are doubly connected loops in which one arm is a superconductor and one arm is a normal metal, oscillates as a function of magnetic field with a fundamental period corresponding to a flux quantum h / 2 e through the area of the loop. While the magnetoresistance of an Andreev interferometer is symmetric with respect to the magnetic field, the thermopower can be either symmetric or antisymmetric, depending on the topology of the sample. The temperature dependence of the thermopower oscillations is nonmonotonic. This nonmonotonic behavior does not appear to be related to the reentrance observed by many groups in the conductance of normal-metal/superconductor (NS) structures.     

Study of interface liquation in metal systems with chemical interaction

The interface melting point in binary metal systems exhibiting chemical interaction is estimated. Calculations for the Bi-Tl systems satisfactorily agree with the experimental results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, 94–97, January, 1976.In conclusion the authors wish to express their appreciation to S. N. Zadumkin and Associate Professor A. A. Shebzykhov for their assistance.     

Phase slippage at the interface: normal metal/sliding charge-density wave

Phase slippage is required at the current electrodes of quasi-one-dimensional conductors with a charge density wave (CDW) ground state for the conversion from free to condensed carriers. We have performed at the ESRF high-resolution X-ray measurements of the spatially varying shift q(x) of the CDW satellite wave vector between current contacts on a thin NbSe₃ whisker in the sliding state. Applying direct currents, we observe at 90 K a steep exponential decrease of the shift within a few hundred microns from the contact. The CDW strain profile q(x) reflects the carrier conversion process, via nucleation and growth of phase-dislocation loops. Pulsed current measurements of the shift q show important differences between pulsed and dc current data, revealing a spatially dependent relaxational behaviour of the CDW strain. Using time-resolved high spatial resolution X-ray we observe at 300 μm from the electrode a stretched exponential-type decay of the shift q(t) upon switching off the current (T=75 K): q(t)=q₀[exp(−t/τ)^μ] with τ=23 ms and μ=0.36.     

Surface waves at the interface between a metal and a photovoltaic-photorefractive crystal

We investigate surface waves at the interface between a metal and a photovoltaic-photorefractive (PP) crystal. These surface waves appear in several forms: delocalized surface waves, shock surface waves, and localized surface waves. Only localized surface waves have limited energy. We demonstrate that the transverse sizes of localized surface waves decrease with an increase in the propagation constant and the amplitudes of localized surface waves increase with the propagation constant. The stability of localized surface waves is investigated numerically and it is found that they are stable.     

On interface thermal resistance associated with thermal vibrations

This Letter generalizes the well-known acoustic mismatch theory of interface thermal resistance by inclusion into consideration a broad class of thermal vibrations that were excluded from that theory by the imposition in it of the Sommerfeld radiation condition, which is required for the theory of sound but is not relevant for the analysis of heat transport. This extension preserves the main ideas of the acoustic mismatch theory but provides much better estimates for the interface resistance, which have an order-of-magnitude agreement with experiments previously published by others.     

Surface states induced by metal atoms at the Si/electrolyte interface

Metal atoms have been chemically deposited on n-Si and p-Si and the obtained deposits have been characterized with Auger electron spectroscopy. The obtained samples have been used as electrodes in acetonitrile electrolyte. The electrochemical studies heve been performed using classical current-voltage, impedance and Schottky-Mott measurements, and also subgap photocurrent spectroscopy of the surface states. It appears that the deposited metal atoms do induce surface states on the silicon surface. These surface states have a weak effect on the flatband potential (i.e. no strong pinning of the Fermi level is observed even for monolayer coverage) but the subgap photoyield is increased by several orders of magnitude. The shape of the quantum yield versus photon energy curve points to surface states widely distributed through the bandgap. These experiments finally confirm the ability of the subgap photocurrent technique to distinguish between the two kinds of optical processes that may occur between the surface states and the semiconductor bands.     

A study of the thin metal film/fluid interface using surface plasmon-polaritons

Surface plasmon-polaritons have been used as the probe to study the interface between a thin polycrystalline gold film and a series of aliphatic alcohols. It is found that fitting the reflectivity data to theoretical predictions from Fresnel's equations for layered structures produces variations in both the apparent thickness and the dielectric constants of the gold film which depend on the adjacent alcohol. These variations are far greater than the experimental error and lead to the conclusion that a very thin (<0.5 nm) surface roughness layer has a significant influence on the results from this type of experiment.     

Information and complexity measures in the interface of a metal and a superconductor

Fisher information, Shannon information entropy and Statistical Complexity are calculated for the interface of a normal metal and a superconductor, as a function of the temperature for several materials. The order parameter $\mathrm{\Psi }(\mathbf{r})$ derived from the Ginzburg–Landau theory is used as an input together with experimental values of critical transition temperature $T_c$ and the superconducting coherence length ${\xi }_0$. Analytical expressions are obtained for information and complexity measures. Thus $T_c$ is directly related in a simple way with disorder and complexity. An analytical relation is found of the Fisher Information with the energy profile of superconductivity i.e. the ratio of surface free energy and the bulk free energy. We verify that a simple relation holds between Shannon and Fisher information i.e. a decomposition of a global information quantity (Shannon) in terms of two local ones (Fisher information), previously derived and verified for atoms and molecules by Liu et al. Finally, we find analytical expressions for generalized information measures like the Tsallis entropy and Fisher information. We conclude that the proper value of the non-extensivity parameter $q?1$, in agreement with previous work using a different model, where $q?1.005$.     

Factors influencing the ballistic impact resistance of elastomer-coated metal substrates

An experimental study was carried out of various factors affecting the ballistic penetration resistance of elastomer/steel bilayers. For blunt penetrators, the contribution of the coating to performance is optimized using the hardest substrates, front surface placement of the elastomer, and (when normalizing by added weight) thin, ca. 2–3?mm, coatings. These results, none of which are predicted by existing models, evince the marked coupling of coating and substrate in the impact response of the bilayer. We also show that nanoparticle fillers have a modest effect on ballistic performance of polyurea coatings, changing the penetration velocity by a few percent or less. This contrasts with the linear dynamic mechanical behavior, which shows much more significant increases in energy absorption due to nano-reinforcement.