Surface and interface phonons and related topics

We analyze the state of the art of surface and interface phonons with an emphasis on their relevance to many aspects of surface and interface physics.     

光散射法同时测量气液二元体系的黏度、界面张力和热、质扩散系数的研究

当气液二元体系处于宏观热力学平衡状态时,表面与体相的波动弛豫时间具有不同量级,通过调节散射体积和改变采样时间,利用表面光散射实验系统可以同时探测到来自界面处表面波及体相中温度和浓度的波动信息。本文在已有的表面光散射实验系统上,以正庚烷与二氧化碳二元系统为例,同时实现了该体系黏度、界面张力和热、质扩散系数的测量,其扩展不确定度分布为3.0%,3.7%,20%,4.3%(k=2)。实验所得到的数据与文献进行了对比,其偏差在不确定度范围内,证明了本文提出的测量方法可以实现气液二元体系四种性质的同时测量,且测量精度可以满足一般工程应用。     

Surface and near-surface passivation, chemical reaction, and Schottky barrier formation at ZnO surfaces and interfaces

Using a combination of depth-resolved cathodoluminescence spectroscopy, electronic transport, and surface science techniques, we have demonstrated the primary role of native defects within ZnO single crystals as well as native defects created by metallization on metal-ZnO Schottky barrier heights and their ideality factors. Native defects and impurities resident within the ZnO depletion region as well as defects extending into the bulk from the intimate metal-ZnO interface contribute to barrier thinning of, carrier hopping across, and tunneling through these Schottky barriers. Chemical reactions at clean ZnO-metal interfaces lead to metal-specific eutectic or oxide formation with pronounced transport effects. These results highlight the importance of bulk crystal quality, surface cleaning, metal interaction, and post-metallization annealing for controlling Schottky barriers.     

Gas—liquid interfaces of room temperature ionic liquids

The structure of the gas-liquid surface of dimethylimidazolium chloride has been studied using atomistic simulation. We find that there is a region of enhanced density immediately below the interface in which the cations are oriented with their planes perpendicular to the surface and their dipoles in the surface plane. There is negligible segregation of cations and anions. The temperature dependence of the surface tension is predicted to be anomalously low or be reversed in sign. The vapour-liquid interfaces between mixtures of water and dimethylimidazolium chloride show similar regions of enhanced density and preferential orientation of the cations. Water molecules also show preferential orientation in the interface region and are preferentially adsorbed on the vapour side of the interface. The surface tension decreases with increase in the mole fraction of water.     

Boundary conditions and non-equilibrium thermodynamics

The theory of non-equilibrium thermodynamics is applied to a system of two immiscible fluids and their interface. A singular energy density at the interface, which is related to the phenomenon of surface tension, is taken into account. Furthermore the momentum and the heat currents are allowed to be singular at the interface. Using the conservation laws and the Gibbs' relation for the surface, an expression for the singular entropy production density at the interface is obtained. The linear phenomenological laws between fluxes and thermodynamic forces occurring in this singular entropy production density are given. Some of these linear laws are boundary conditions for the solution of the differential equations governing the evolution of the state variables in the bulk.     

Surface tension and energy in multivariant martensitic transformations: phase-field theory, simulations, and model of coherent interface

The Ginzburg-Landau theory for multivariant martensitic phase transformations is advanced in three directions: the potential is developed that introduces the surface tension at interfaces; a mixed term in gradient energy is introduced to control the martensite-martensite interface energy independent of that for austenite-martensite; and a noncontradictory expression for variable surface energy is suggested. The problems of surface-induced pretransformation, barrierless multivariant nucleation, and the growth of an embryo in a nanosize sample are solved to elucidate the effect of the above contributions. The obtained results represent an advanced model for coherent interface.     

A study of advances in characterization of interfaces and fiber surfaces in lignocellulosic fiber-reinforced composites

This article deals with the aspects of interfacial and surface characterization of natural fibers and their composites. Vegetable fibers and their composites have attracted the attention of scientists worldwide because of their favorable properties. The different chemical modifications of natural fibers and characterization aspects have been discussed. The adhesion between fiber and matrix is a major factor in determining the response of the interface and its integrity under stress. Therefore characterization of the interface is of utmost importance. Both fiber surface and polymer matrix surface can be modified to obtain a strong interface. Various treatments being used for the lignocellulosic surfaces and the characterization techniques have been illustrated. The four main techniques of interfacial characterization that are enumerated in this article are the micromechanical techniques, spectroscopic, microscopic and swelling techniques. The micromechanical techniques like fiber pull-out and fragmentation have been dealt with giving emphasis to experimental aspects. Recent studies dealing with interfacial study of different lignocellulosic fiber reinforced composites have also been cited.     

Hydrodynamic response and free surface modes for two immiscible fluids

We consider a system consisting of two immiscible fluids and their interface. The equilibrium interface is assumed to be planar. The velocity fields in the fluids are described by the linearized Navier-Stokes equations with appropriate boundary conditions at the interface. Explicit expressions for the response of the system to arbitrary bulk and/or surface forces are derived. In particular, we consider the transmission and reflection of sound modes and conclude that ultrasonic techniques can be used to measure the coefficient of sliding friction between fluids. In addition, we obtain dispersion relations for the free surface modes.     

Molecular dynamics study of water in contact with the TiO2 rutile-110, 100, 101, 001 and anatase-101, 001 surface

We have carried out classical molecular dynamics of various surfaces of TiO₂ with its interface with water. We report the geometrical features of the first and second monolayers of water using a Matsui Akaogi (MA) force field for the TiO₂ surface and a flexible single point charge model for the water molecules. We show that the MA force field can be applied to surfaces other than rutile (110). It was found that water OH bond lengths, H–O–H bond angles and dipole moments do not vary due to the nature of the surface. However, their orientation within the first and second monolayers suggest that planar rutile (001) and anatase (001) surfaces may play an important role in not hindering removal of the products formed on these surfaces. Also, we discuss the effect of surface termination in order to explain the layering of water molecules throughout the simulation box.     

Experimental measurement of variations in the optical reflection coefficient of water-magnetic liquid interface in an electric field,wave motion,and surface instability

A variation in the reflection coefficient of an interface of two liquids (water and magnetic liquid) in the presence of an electric field is experimentally studied. An increase in the reflection coefficient of the interface is demonstrated. A surface instability of the water-magnetic liquid interface, the wave motion at the interface, and wave interference are observed.     

Silicon surface passivation by static charge

A properly passivated silicon surface is chemically stable, and all interface properties are constant. The silicon dioxide layers fulfil the chemical stability requirements; however, their surface and interface charges have effect on the silicon surface potential barrier. Positive charge is usually assumed at the oxide-silicon interface, thus depletion or inversion layer develops in the case of p and accumulation in the case of n-type silicon.The surface of silicon dioxide can be charged macroscopically by corona charger or by conductive rubber stamp, microscopically by a tip of some scanning probe microscope (STM or AFM). The oxide surface usually retains the charges for a long time, however in the case of ultra-thin or other leaky oxide continuous charging it is necessary to keep the constant surface potential.The main purpose of this work is to summarize the possibilities of charging up the surface, the effect of the surface and interface charge on the surface properties of the silicon. The rearrangement of the surface charges will also be discussed.     

Surface morphology of InGaAs on GaAs(100) by chemical beam epitaxy using unprecracked monoethylarsine, triethylgallium and trimethylindium

Temperature-dependent evolution of surface corrugation and the interface dislocation in In_0.15Ga_0.85As epilayer on GaAs(100) substrate grown by chemical beam epitaxy using unprecracked monoethylarsine have been investigated by atomic force microscope (AFM) and transmission electron microscopy (TEM). AFM images showed that the line direction of surface ridge changes from [011] to [0 1] with increasing temperature. However, TEM micrographs showed that dislocation networks are formed along both [011] and [0 1] directions at the interface. These results indicate that growth kinetics on the terrace and at surface steps generated by the dislocations play an important role in determining the direction of surface corrugation. We suggest that the temperature-dependent change of surface corrugation is caused by an anisotropic surface diffusion on the terrace and different sticking probability of adsorbates on the surface steps which were produced by interface misfit dislocation along the two orthogonal surface directions.     

Colloids in external electric and magnetic fields: Colloidal crystals, pinning, chain formation, and electrokinetics

The motion of dilute and concentrated dispersions of colloids by external electric or magnetic fields is discussed. Electrokinetics is studied for colloids in confinement, where the confining walls can be flat or rough. As an example for a rough wall superhydrophobic surfaces are chosen. It is shown that the reduced friction at the water-air interface is insufficient to enhance electro-osmosis. Magnetic particles are pulled through a crystalline matrix formed by nonmagnetic colloids to investigate local melting and recrystallization of a crystalline matrix. The average strain field is calculated and the reorganization processes are compared to those induced by shear fields. Using single domain, magnetically blocked particles of different shape and surface characteristics, the interplay between particles, their environment and an external field is investigated.     

表面等离激元的聚焦与波导增强

近年来,表面等离激元学（plasmonics）已经形成一个新的学科热点.电子在金属与介质界面的集体振荡行为形成一种元激发——表面等离激元（surface plasomon polariton,SPP）.由于其具有特殊的耦合与传播性质,与SPP相关的器件设计与应用成为目前纳米光子学领域的国际前沿研究方向.文章介绍了利用微...     

Probing simultaneously the volume and surface structure of nanospheres adsorbed at a solid-liquid interface by GISANS

We demonstrate in this paper the possibilities offered by Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of solid/liquid interfaces. We present experimental results obtained by Specular Neutron Reflectivity (SNR) and GISANS on a model system made of silica nanospheres adsorbed on a silicon wafer by electrostatic interactions both at solid/air interface and solid/liquid interfaces. At the solid/liquid interface, we demonstrate that grazing incidence scattering enables to discriminate the surface and the bulk scattering. The surface structure factor derived from GISANS shows that the nanospheres are organized as a repulsive liquid system, with a surface fraction occupation consistent with values obtained by SNR. This original setup highlights a direct correlation between the structure of the silica nanospheres in solution and their organization on the surface: due to the strong electrostatic repulsions between spheres, their organization at the surface is close to the projection in 2D of the 3D organization of the nanospheres in solution.     

Surface passivation of III-V semiconductors for future CMOS devices—Past research, present status and key issues for future

Currently, III-V metal-insulator-semiconductor field effect transistors (MISFETs) are considered to be promising device candidates for the so-called “More Moore Approach” to continue scaling CMOS transistors on the silicon platform. Strong interest also exists in III-V nanowire MISFETs as a possible candidate for a “Beyond CMOS”-type device. III-V sensors using insulator-semiconductor interfaces are good candidates for “More Moore”-type of devices on the Si platform. The success of these new approaches for future electronics depends on the availability of a surface passivation technology which can realize pinning-free, high-quality interfaces between insulator and III-V semiconductors.This paper reviews the past history, present status and key issues of the research on the surface passivation technology for III-V semiconductors. First, a brief survey of previous research on surface passivation and MISFETs is made, and Fermi level pinning at insulator-semiconductor interface is discussed. Then, a brief review is made on recent approaches of interface control for high-k III-V MIS structures. Subsequently, as an actual example of interface control, latest results on the authors’ surface passivation approach using a silicon interface control layer (Si ICL) are discussed. Finally, a photoluminescence (PL) method to characterize the interface quality is presented as an efficient contactless and non-destructive method which can be applied at each step of interface formation process without fabrication of MIS capacitors and MISFETs.     

Wetting, drying, and layering of colloid-polymer mixtures at porous interfaces

The influence of interface porosity on the wetting properties of colloid-polymer mixtures is studied within density functional theory for the Asakura-Oosawa-Vrij model at the surface of a quenched hard-sphere matrix. While the porosity hardly changes the location of the transition from partial to complete wetting at colloidal bulk gas-liquid coexistence, the onset of wetting, as signaled by the first discontinuous layering transition, can be efficiently controlled by tailoring the porosity. We furthermore find that the penetrability of the porous interface induces complete drying into the matrix upon approaching capillary coexistence.     

Effects of surface and interface energies on the bending behavior of nanoscale multilayered beams

A modified continuum model of the nanoscale multilayered beams is established by incorporating surface and interface energies. Through the principle of minimum potential energy, the governing equations and boundary conditions are obtained. The closed-form solutions are presented and the overall Young's modulus of the beam is studied. The surface and interface energies are found to have a major influence on the bending behavior and the overall Young's modulus of the beam. The effect of surface and interface energies on the overall Young's modulus depends on the boundary condition of the beam, the values of the surface/interface elasticity constants and the initial surface/interface energy of the system. The results can be used to guide the determinations of the surface/interface elasticity properties and the initial surface/interface energies of the nanoscale multilayered materials through nanoscale beam bending experiments.     

Local friction at a sliding interface between an elastomer and a rigid spherical probe

This paper reports on spatially resolved measurements of the shear stress distribution at a frictional interface between a flat rubber substrate and a glass lens. Silicone rubber specimens marked close to their surface by a colored pattern have been prepared in order to measure the surface displacement field induced by the steady-state friction of the spherical probe. The deconvolution of this displacement field then provides the actual shear stress distribution at the contact interface. When a smooth glass lens is used, a nearly constant shear stress is achieved within the contact. On the other hand, a bell-shaped shear stress distribution is obtained with rough lenses. These first results suggest that simple notions of real contact area and constant interface shear stress cannot account for the observed changes in local friction when roughness is varied.     

Kinetic roughening,global quantities,and fluctuation–dissipation relations

Growth processes and interface fluctuations can be studied through the properties of global quantities. We here discuss a global quantity that not only captures better the roughness of an interface than the widely studied surface width, but that is also directly conjugate to an experimentally accessible parameter, thereby allowing us to study in a consistent way the global response of the system to a global change of external conditions. Exploiting the full analyticity of the linear Edwards–Wilkinson and Mullins–Herring equations, we study in detail various two-time functions related to that quantity. This quantity fulfills the fluctuation–dissipation theorem when considering steady-state equilibrium fluctuations.