梯度表面能材料表面上液滴形状的数值模拟

本文建立了固体表面上静止液滴的势能方程,根据能量最小化原理,当系统总势能取得最小值时,液滴将处于平衡状态.采用有限元方法,将初始自由液面离散化,通过曲面上节点的虚拟位移,改变自由液面的拓扑结构,使系统总势能取得最小值,从而得到静止液滴的形状.并应用该方法对均质表面和梯度表面能材料表面上的液滴界面进行了数值模拟,得到了均质材料表面和梯度表面能材料表面上静止液滴的界面形状及分布.     

表面不平整对半无限超晶格表面电磁耦子的影响

本文讨论表面不平整对半无限超晶格表面电磁耦子(polariton)的影响。文中推导了平整表面半无限超晶格情形,Maxwell方程的格林函数。由此导出表面电磁耦子的色散关系。主要结论是:在表面不平整情形,将出现新的模式——表面型TE模表面电磁耦子,可资实验检验。 关键词：     

Dispersion and damping of a surface plasmon polariton on a one-dimensional randomly rough metal surface

Abstract

By the use of the reduced Rayleigh equation for the amplitude of a surface plasmon polariton on a one-dimensional randomly rough metal surface that is in contact with vacuum, we calculate the dispersion and damping of the surface electromagnetic wave to the lowest nonzero order in the rms height of the surface. It is found that the frequency of the surface plasmon polariton is depressed by the surface roughness. The attenuation of the surface plasmon polariton in the long wavelength limit is due primarily to its scattering into other surface plasmon polaritons, while in the short wavelength limit it is due primarily to its roughness-induced scattering into volume electromagnetic waves in the vacuum. The energy mean free path of the surface plasmon polariton is shorter on a randomly rough metal surface than it is on a lossy planar metal surface, and the surface plasmon polariton is more tightly bound to a rough surface than to a planar one.     

Shear viscosity of polymer and surfactant monolayers

The surface shear viscosity of monolayers formed at the surface of water by adsorbed polyethyl- eneoxyde and by stearic acid is measured as a function of the surface pressure of the monolayer using a new surface viscometer. The principle of the viscometer is the measurement of the drag force on a circular disk undergoing a uniform translation at the water surface: a hydrodynamic model based on the lubrication approximation allows a calculation of the surface viscosities from the absolute measurement of the drag forces. Received: 26 August 1999     

利用激光超声技术研究表面微裂纹缺陷材料的低通滤波效应

利用激光激发声表面波的理论模型,研究了被激发宽带声表面波在具有表面微裂纹缺陷金属材料上的传播特性.对具有不同形状的表面缺陷模型进行了数值分析.结果表明:表面微裂纹缺陷有明显的低通效应,缺陷深度越大高频截止频率就越低,缺陷深度与低通滤波的截止频率呈近似线性关系;缺陷的宽度增大对表面波透射能量有明显的衰减作用. 关键词： 激光超声 声表面波 有限元方法 低通滤波器     

Design of a Reflective Aspherical Surface of a Compact Beam-Shaping Device

A compact beam-shaping device with a reflective aspherical surface is proposed. The device converts a circular symmetric Gaussian beam from a laser into a uniform distribution on a target plane. The device consists of a laser, a reflective aspherical surface formed on the base plane inclined by 45° against the optical axis, and a spacer. The surface is designed for an optical device used as a transmitter of indoor wireless optical communication, which is one of the promising applications. The designed surface is obtained by approximation using polynomial. Beam shaping of a simulated surface and a uniform intensity distribution on the target plane is obtained. The intensity distribution generated by the surface is numerically simulated and evaluated if the surface is misaligned. It is clarified that the generated distribution is tolerable for the misalignment.     

The surface composition of the silver—Gold system by Auger electron spectroscopy

The surface composition of polycrystalline AgAu alloy foils is studied by Auger electron spectroscopy. The intensities of principal Auger peaks over a wide range of electron energies are obtained as a function of alloy bulk composition for the clean equilibrated surfaces. Their ratios are compared with ratios expected for a surface showing no surface segregation, and for a surface obeying the regular solution monolayer model that predicts silver surface segregation. The experimental results give evidence for enrichment of the surface with silver, but to an extent less than predicted by the regular solution model.     

The influence of contact surface microstructure on vacuum arcstability and voltage

The authors present the results of DC vacuum arc lifetime and voltage measurements for contacts with different surface microstructures. This was realized by treating the contact surface with emery paper of varying roughness. The contact surface microstructure was found to have a large effect on the DC arc lifetime (several tens of times difference at the most) and arc voltage (30% difference at the most). The mechanism of the surface microstructure effect on DC arc stability was analyzed and is explained preliminarily. The rougher the contact surface is, the longer the arc lifetime and the more stable. The arc itself has a tendency to condition the surface in a way that is unfavorable for a sustained arc lifetime. The crater size for a rough surface is smaller than for a smooth one. The rougher the contact is, the lower the arc voltage (both DC and HF components). The arc erosion has a tendency to increase the arc voltage. It is probable that type I cathode spots (fast motion, small crater size) correspond not only to the surface contamination, but also to the surface roughness     

Symmetric Surface Momentum and Centripetal Force for a Particle on a Curved Surface

The Hermitian surface momentum operator for a particle confined to a 2D curved surface spanned by orthogonal coordinates and embedded in 3D space is expressed as a symmetric expression in derivatives with respect to the surface coordinates and so is manifestly along the surface. This is an alternative form to the one reported in the literature and usually named geometric momentum, which has a term proportional to the mean curvature along the direction normal to the surface, and so "apparently" not along the surface. The symmetric form of the momentum is the sum of two symmetric Hermitian operators along the two orthogonal directions defined by the surface coordinates. The centripetal force operator for a particle on the surface of a cylinder and a sphere is calculated by taking the time derivative of the momentum and is seen to be a symmetrization of the well-known classical expressions.     

Observation of surface plasmon splitting on Ag(111) by electroreflectance spectroscopy

The spectral dependence of electroreflectance near the surface plasma frequency of Ag(111) has been measured for various degrees of surface roughness. The experiments clearly show a splitting of the surface plasma resonance on increasing the roughness of the sample. The results agree well with a recent theory which predicts a splitting of the surface plasmon dispersion relation on a statistically rough surface.     

Giant Rashba-type spin splitting at polar surfaces of BiTeI

On the basis of relativistic ab initio calculations, we show that both Te- and I-terminated surfaces of the polar layered semiconductor BiTeI hold surface states with a giant Rashba-type spin splitting. The Te-terminated surface state has nearly isotropic free-electron-like dispersion with a positive effective mass, which along with the giant spin splitting makes BiTeI fulfilling the requirements demanded by many semiconductor-spintronics applications. The I-terminated surface state with its negative effective-mass dispersion reproduces nicely the situation with the Rashba-split surface state on surfaces of noble-metal based surface alloys. The crucial advantage of BiTeI as compared with the surface alloys is the location of the I-terminated surface state in a quite wide band gap.     

A new surface phase in liquid normal-alkanes

A new surface phase is found in liquid normal-alkanes. X-ray and surface tension measurements show the formation of a crystalline monolayer on the surface of the liquid at temperatures up to 3°C above the bulk solidification temperature, T_f. The molecules in the monolayer are hexagonally packed and oriented normal to the surface. A single solid monolayer persists down to T_f, thus exhibiting a very limited partial wetting. The new surface phase is obtained only for chain lengths 14<n50. Its vanishing for n14 is interpreted as a possible transition from surface freezing to surface melting behaviour. The measurements are satisfactory accounted for within a simple theory based on surface energy cosiderations.     

三维随机粗糙面与目标复合电磁散射的FDTD方法

用时域有限差分方法(FDTD)研究三维周期性延拓的随机粗糙面与上方目标复合电磁散射.用周期性延拓消除数值计算中截取有限大小粗糙面产生的边缘效应,讨论一个周期单元粗糙面的边长与其相关长度之间的关系.给出在FDTD方法中向粗糙面加载入射波的方法,建立了粗糙面上单个三维目标的复合散射FDTD计算模型.数值结果给出粗糙面与目标散射的近场分布,应用近远场变换得到全方位散射角的双站散射系数.比较了三维与二维散射模型的区别.结果显示当粗糙面上放置目标时,其后向散射显著增强.     

Variational problems on the contact of heterogeneous phases

The variational formulation of general problems of capillary surface equilibrium (problems on a drop on a solid surface, drop on the surface of a drop of another liquid, partly faceted capillary surface) is considered. For the problem of a partly faceted capillary surface, the Legendre transformation between the equilibrium form and surface energy density is used.     

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF₂ underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.     

Study of a surface critical phenomenon associated with surface segregation in Cu---Ag alloys

This paper presents a modified regular solution formalism for surface segregation in substitutional alloys which distinguishes between bond energies at the surface and in the bulk of a solid solution. The differences between surface and bulk energies are ascribed to strain energy effects associated with misfitting solutes. Experimental measurements of surface composition on (111) surfaces of Cu---Ag alloys dilute in Ag are reported and show the existence of a surface phase transition, which manifests itself as an abrupt surface composition change at temperatures below 788 K. Similar measurements on (100) surfaces show no comparable critical phenomena down to temperatures as low as 523 K, indicating a strong anisotropic behavior of the surface phase transition. The data are compared with the model to obtain model-based estimates of the surface critical temperatures and the surface regular solution constants for both surface orientations.     

The effect of surface alloying on the surface properties of activated CdSe films

Changes in surface potential, surface conductivity, mobility in a field, and Hall electron mobility in activated CdSe films with a surface alloy of indium are studied. The strong enrichment of charge carriers on the surface is explained by the presence of a positive charge on the surface, neutralizing the negative charge of oxygen atoms, with the latter being neutralized as a result of interaction of metal atoms with oxygen adsorbed on the surface. The possibility of determining the parameters of volume traps and the absolute surface potential of the film by experiments with surface alloying is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 86–90, September, 1972.     

Theoretical modeling of hard X-ray surface modes in a periodic multilayer

The excitation of hard X-ray surface modes of a periodic multilayer is studied with the help of theoretical modeling. It is found that a hard X-ray surface mode can appear in a specific periodic multilayer coated with a high-density reflecting layer. The generation of the hard X-ray surface modes is shown to be effective only at a certain set of the structural parameters of the multilayer. A method for the calculation of the propagation (attenuation) length of the surface mode running in the periodic multilayer is described. The excitation of the hard X-ray surface modes is compared with that of optical surface modes in photonic crystals. The relationship between the surface modes and guided modes of periodic multilayers is discussed.     

On the effect of microscopic roughness of the metal surface on the surface plasmon dispersion relation and photoemission

The effect of microscopic surface roughness on the opical characteristics of metal is considered. The field near the rough surface has been calculated on the basis of integral equations containing only smoothly varying field components. It appears that the influence of surface plasmons can cause, as a result of drastic enhancement of the field at the surface, an increase by several orders in such observed surface effects as photoemission and Raman scattering by adsorbed molecules. The results of calculation are compared with the experimental data obtained from the study of photoemission from silver with rough surface. Expressions have been derived for the dispersion relation for surface plasmons on a rough surface.     

Three-dimensional tomography of the beryllium fermi surface: surface charge redistribution

The discontinuity in the lattice periodic potential at surfaces often leads to the creation of new electronic surface states. We developed a photoemission based Fermi surface tomography whose surface sensitivity allowed us to quantify the charge redistribution on the Be(0001) surface. The volume enclosed by the bulklike Fermi surface is significantly reduced at the surface, consistent with the charge transfer to the two surface states as estimated from the area within their two-dimensional Fermi contours. This result represents the first quantification of the charge redistribution on a natural surface termination.