On the interaction between chemisorbed atoms at transition metal surfaces

A model hamiltonian is derived describing the interaction of two adsorbates. The nonorthogonality of the basis set is converted into a renormalization of the matrix elements. The interaction energy, direct and indirect of two hydrogen atoms and single particle spectral densities are calculated for adsorption on a semi infinite simple cubic solid. Correlation effects are included by a variational ansatz.     

Nature of the short-range interaction between noble gas atoms and metal surfaces

I propose that an interpretation of the interaction of noble gas atoms with metal surfaces as predominantly physisorbing provides the best explanation for the systematics of their binding energies and surface dipoles, as well as for the tendency of noble gas atoms to bind in low coordinated sites. In the present context physisorption is defined as a process driven by the overlap of the electrostatic atomic potentials of the interacting species. PACS 68.43.Fg; 68.47.De     

Surface-plasmon-polariton-assisted dipole-dipole interaction near metal surfaces

We investigate the surface plasmon polariton (SPP)-assisted interaction between two dipoles near a metal surface. The radiation energy from a dipole can excite SPPs and transport to another dipole through the channel of the localized SPP modes. This energy transfer can be much more efficient than direct energy transfer via dipole-dipole radiation interaction in free space. A simple analytical model is proposed to describe the underlying physics behind the influence of SPP on the dipole-dipole interaction energy, and it predicts a wide variety of complicated interaction features that agree well with rigorous calculations.     

Surface friction constant and range of dynamical interaction between adatoms on metal surfaces

The electronic contribution to the surface friction constant of an adatom on a metal surface is calculated using: (i) the Dirac density matrix for an infinite barrier model of an inhomogeneous electron gas, and (ii) two simple models of screened potentials at the surface based on reliable asymptotes in and outside the surface respectively. Though the results are clearly approximate, attention is drawn especially to the predictions of the models concerning long-range dynamic interactions between adatoms on metal surfaces.     

Band effects and the dipole interaction between two adatoms on a metal surface

The contribution of band effects to the adatom interaction energy is investigated to second order in perturbation theory. These are found to bring an important correction to the dipole law derived recently by Kohn and Lau.     

Van der Waals interaction between a molecule and a metal surface: Effect of spatial dispersion

In this paper the effect of spatial dispersion on the dielectric response of a semi-infinite metal is investigated in the hydrodynamic approximation, and the result is used to evaluate the van der Waals force between a molecule and a metal surface. It is shown that corrections to the image potential result arising out of spatial dispersion can be evaluated systematically.     

分子尺度上水和金属表面的相互作用

虽然水普遍存在,但人们在分子尺度上对水与固体表面的相互作用的理解却仍然处在初始阶段.文章简述了20年来人们对水在贵金属表面的吸附和浸润过程进行微观尺度上研究的进展,分析和讨论了水和表面作用的一般规律和所获得的经验教训,特别着重讨论了对上世纪80年代人们提出的经典双层冰模型的修正.     

分子尺度上水和金属表面的相互作用

虽然水普遍存在,但人们在分子尺度上对水与固体表面的相互作用的理解却仍然处在初始阶段.文章简述了20年来人们对水在贵金属表面的吸附和浸润过程进行微观尺度上研究的进展,分析和讨论了水和表面作用的一般规律和所获得的经验教训,特别着重讨论了对上世纪80年代人们提出的经典双层冰模型的修正.     

Spatial and angular distributions of third harmonic generation from metal surfaces

Third harmonic generation from planar and spherical metal surfaces is studied theoretically through the standard Green function method, so that the results are not affected by the uncertainty associated with previous simplified models. In general the pattern of the non-linear scattering loosely resembles the pattern of Mie scattering. The strong backward scattering is uniquely related to the non-linear process. These results differ significantly from the predictions of the surface charge model. Received: 20 May 1998 / Received in final form: 25 August 1998 / Accepted: 1st September 1998     

Direct observation of adatom-substitutional atom interaction on dilute metal alloy surfaces

The field ion microscope is used to study interactions of a migrating tungsten adatom with substitutional rhenium atoms in the (110) plane of a W-3%Re alloy. By observing about 300 migration periods on a single (110) surface plane of a small field ion emittier, each position of the adatom with respect to deduced Re atom locations can be identified. The interaction is found to be attractive with a strength of 90 ± 7 meV at the closest equilibrium separation, and repulsive with a strength of at least 80 meV at the second closest separation. No interaction could be observed for larger separations indicating a strength of less than 10 meV. Results of a control experiment, diffusion of single W adatoms on the (110) plane of pure W, are also presented for comparison.     

An experiment concerning the dispersion forces between very small metal spheres

The London-Van der Waals attraction between very small spheres is determined in an experiment with colloidal particles. The measured value of the attraction constant is a function of the particle size. It is ten times smaller than values calculated with the macroscopic theory of dispersion forces on the basis of data for a bulk material.     

Comparison of the third-order dispersion terms of interaction between chiral molecules

Using a quantum electrodynamic approach, the coupling between chiral molecules derived from the exchange of three virtual photons of the electric dipole type is investigated. The resulting interaction potential, which involves the first nonlinear polarizability of the molecules, is compared with a previously derived interaction potential involving the optical activity of the molecules; the latter is accounted for by the exchange of two virtual photons, one being electric dipolar and the other being electric quadrupolar or magnetic dipolar. The symmetry properties of the new term is considered and its quasi-static limit is derived. It appears that the two interaction terms, which both are third-order dispersion processes, might have the same order of magnitude; thus none can a priori be neglected and both might equally contribute to the possibility of a helical ordering.     

Dynamical phenomena including many body effects at metal surfaces

In this contribution, we give a brief survey of some elementary many body processes observable at surfaces. We begin the survey by discussing how the electron ground state would behave and look like in real space at surfaces. Next, we discuss how these electrons behave when they are perturbed by external fields characterized by ultrashort time scales. We follow this with a discussion of how the dynamics of electrons would then affect the motion of adsorbates on surfaces. Finally, we cite some possible technological applications utilizing this knowledge. We also discuss possible trends or directions of scientific research in this century.     

氢分子间色散相互作用能的自然轨道泛函

理论上对分子间色散相互作用能的精确计算一直是个难点问题.密度矩阵泛函基于非定域量一阶密度矩阵为基本变量,它与色散相互作用起源于电子间的非定域关联特性相吻合.论文以最简单的氢分子为研究对象,通过分析两相互平行的氢分子间色散相互作用能,构造出了该体系中色散相互作用能的自然轨道泛函.结果表明:描述该体系中色散相互作用能的自然轨道泛函形式为包含有4个轨道的非交换和库伦积分.该结果对发展色散相互作用能的密度矩阵泛函理论具有重要的参考价值.     

Signature of a chemical bond in the conductance between two metal surfaces

Conductance in monatomic metal contacts is quantized; it increases in discrete steps of one conductance quantum 2e(2)/h. By contrast, in a vacuum barrier between two metal surfaces we find that conductance increases linearly and continuously with the interaction energy between individual atoms. This behavior shows unambiguously that current flow between single atoms is a measure for their chemical interaction. In the controlled environment of a scanning tunneling microscope it should allow us to study the formation of covalent bonds up to the point where these atoms finally jump into contact.     

Spatial inhomogeneity of the interaction between bistable ferromagnetic wires

An experimental study and a theoretical calculation are presented of the hysteresis loop of two bistable ferromagnetic wires. A new effect—an asymmetry of the shift of the switching field at the first and the second Barkhausen jump—is found experimentally. The effect is explained as a consequence of the spatial dependence of the stray field. It is also reproduced within our recent calculation of the stray field from the magnetisation profile. Theoretical results qualitatively agree with the experimental data.