Moment of van der Waals forces between anisotropic bodies

We find the moment of the van der Waals forces between two anisotropic uniaxial thick plates separated by a thick gap filled with isotropic material. Errors which occurred in [2, 3] in a discussion of this effect are pointed out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1637–1643, November, 1978.In conclusion, we thank V. L. Ginzburg, who brought the existence of the effect discussed in this article to the attention of the author.     

Yang-Mills potentials and the van der Waals force between hadrons

The colour-induced magnetic dipole interaction between hadrons is discussed. Fermion motion in a gauge field obtained by solving the classical Yang-Mills equations is considered. It is shown that the spectrum of stationary fermion states is discrete and bound states are colourless. The long range asymptotic behaviour of the gauge potential results in the van der Waals interaction of hadrons.     

First-principles theory of van der Waals forces between macroscopic bodies

We present a first-principles method for the determination of the van der Waals interactions for a collection of finite-sized macroscopic bodies. The method is based on fluctuational electrodynamics and a rigorous multiple-scattering method for the electromagnetic field. As such, the method takes fully into account retardation, many-body, multipolar, and near-fields effects. By application of the method to the case of two metallic nanoparticles, we demonstrate the breakdown of the standard 1/r(2) distance law as the van der Waals force decays exponentially with distance when the nanoparticles are too close or too far apart.     

原子力显微镜探针耦合变形下的微观扫描力研究

原子力显微镜(AFM)的微探针系统是典型的微机械构件，它在接触扫描过程处于耦合变形状态.采用数值模拟方法探究恒力模式下探针耦合变形对微观扫描力信号、微观形貌信号的影响.研究表明，AFM的恒力模式扫描中，法向扫描力并不是恒定大小，与轴向扫描力存在耦合作用，在粗糙峰峰值增加阶段，二力均增加；在粗糙峰峰值减小阶段，二力均减小；该耦合作用随形貌坡度、针尖长度等增加而加强.微观形貌的测试信号和横向扫描侧向力信号受探针耦合变形影响较小，但侧向力与形貌斜率密切相关，且其极值点与形貌极值点存在位置偏差，这些结果均与原子力 关键词： 原子力显微镜 探针悬臂梁 耦合变形 扫描力     

The van der Waals interaction energy between a void and a metal surface

The plasmon part of the van der Waals interaction energy between a void and a metal surface is calculated. In the limit of large z₀ (distance between the void and the surface), the interaction energy is shown to be proportional to z^-3₀ and 2 to 5 times larger than the elastic energy for copper.     

Resonant enhancement and dissipation in nonequilibrium van der Waals forces

Dispersion forces between molecules that are in relative motion, coupled to baths at different temperatures, or in excited states, are calculated using a Green function Liouville space expansion that extends the celebrated McLachlan response theory to the nonlinear regime. Our dynamical theory is applicable to systems that may be in any initial nonequilibrium state and that are subject to an arbitrary time-dependent coupling. In contrast to equilibrium forces which are attractive, nonequilibrium forces may be attractive or repulsive, exhibit chemically specific resonances, are far stronger, and may be nonconservative (with either positive or negative dissipation).     

Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure–distance dependence p  1/D³. It is demonstrated that a layer (oxide or water) at any of the surfaces influences the pressure up to distances, which are an order of magnitude larger than its own thickness. A jump on the p(D) curve is expected at contact of the adsorbed liquid layers. The retardation of van der Waals forces at 5 < D < 20 nm has the similar effect on the pressure as 1 nm oxide layers. At the far end of this range the pressure decreases by 30% due to the retardation. Nanoscale roughness plays a great role when the surfaces are close-to-contact, the crucial factor is the height distribution of asperities. However, their curvature and surface density are also important, as well as the amount of adsorbed water.     

On the macroscopic theory of temperature-dependent van der Waals forces

We give a simple derivation of the van der Waals free energy of interaction between two semiinfinite media, including effects of nonzero temperature and retardation. The method, an extension of one used by van Kampen and co-workers at the short-distance and low-temperature limits, considers the free energy of electromagnetic surface modes in the region between the two media. The result is the same as derived by Lifshitz and co-workers using Green's function techniques.     

范德华作用和静电作用下的二元粒子自组装

采用简单粗粒化粒子模型,通过郎之万动力学模拟研究了具有范德华作用和静电作用的二元粒子自组装．研究发现,通过改变粒子尺寸和粒子间作用强度,二元粒子能够自发形成各种聚集结构,如球 形、堆叠层状与管状结构．利用两亲性分子或两嵌段聚合物自组装理论,解释了二元粒子聚集结构的形成规律．当向溶液中加入反电荷离子时,模拟表明粒子聚集结构在相图中的分布出现了明显偏移．     

Atomic-resolution dynamic force microscopy and spectroscopy of a single-walled carbon nanotube: characterization of interatomic van der Waals forces

We report atomic-resolution imaging and site-specific quantitative force measurements on a single-walled carbon nanotube by dynamic force microscopy and three-dimensional force field spectroscopy at low temperatures. The topography imaged in the attractive force regime reflects the trigonal arrangement of the hollow sites as maxima. Individual force curves were unambiguously assigned to carbon atoms and hollow sites, respectively. Site-specific quantitative evaluation revealed that the short-range interatomic van der Waals forces are responsible for the atomic-scale contrast.     

On the thermodynamics of contact interaction in an atomic force microscope

Contact interaction in an atomic force microscope is considered in terms of the thermodynamic approach. It is shown that hysteresis observed when a sample is probed in the vertical direction is due to the surface energy-work thermodynamic cycle. The force of sample-tip interaction is calculated for the case when the tip is a paraboloid of revolution. Fluctuations of the basic thermodynamic parameters are found. The role of electrocapillary forces is considered. A new method of spectroscopy in the lateral force mode is suggested.     

A comment on the common one-dimensional derivation of the van der Waals forces

In many physical text-books a simple one-dimensional model is used to derive the characteristic 1/R ⁷-dependence of the attractive van der Waals forces. We show that this calculation is wrong. The long range forces in this simple model are not attractive but repulsive proportional to 1/R ⁶. Only a three-dimensional calculation yields the correct behavior.     

Broadband laser excitation of van der Waals polymers from a cold atomic gas

In this article, we study the molecular states or polymer states excited from a broadband laser, in which case the dipole blockade will be suppressed. As expected, it is shown that more molecular states are observed through broadband laser excitations compared with narrow-band laser excitations. In addition, it is discovered that a larger energy difference, larger detuning, is required to form deeper potential wells.     

Dynamic scanning force microscopy at low temperatures on a van der Waals surface: graphite (0001)

The (0001) surface of highly oriented pyrolytic graphite is studied by scanning force microscopy in both contact and dynamic mode. Low temperatures were necessary for the dynamic mode measurements in order to achieve the required signal to noise ratio. At 22 K, atomic scale structures with 2.46 Å periodicity and trigonal symmetry of the individual maxima were obtained in both modes. Since graphite exhibits a van der Waals surface in good approximation, this result shows that comparatively weak forces of van der Waals type are sufficient for successful imaging in the dynamic mode on the atomic scale. However, since the positions of the observed maxima correspond to the ones found by scanning tunneling microscopy and contact scanning force microscopy, but not to the positions of the carbon atoms, it also opens new questions on the imaging mechanism in the dynamic mode.     

Multi-modal analysis on the intermittent contact dynamics of atomic force microscope

A multi-modal analysis on the intermittent contact between an atomic force microscope (AFM) with a soft sample is presented. The intermittent contact induces the participation of the higher modes into the motion and various subharmonic motions are shown. The AFM tip mass enhances the coupling of different modes. The AFM tip mass is modeled by the Dirac delta function and the coupling effects are analyzed via the Galerkin method. The necessity of applying multi-modal analysis to the intermittent contact problem is demonstrated. Unlike the impact oscillator model which assumes the impact/contact time is infinitesimal, the contact time can be a significant fractional portion in each cycle, especially for the soft sample case and thus results in different dynamic behavior from that of an impact oscillator.     

Atoms near magnetodielectric bodies: van der Waals energy and the Casimir-Polder force

Based on macroscopic QED in linear, causal media, a consistent theory for the Casimir-Polder force acting on an atom positioned near dispersing and absorbing magnetodielectric bodies is presented. The perturbative result for the van der Waals energy is shown to exhibit interesting new features in the presence of magnetodielectric bodies. To go beyond perturbation theory, we start with the center-of-mass equation of motion and derive a dynamical expression for the Casimir-Polder force acting on an atom prepared in an arbitrary electronic state. For a nondriven atom in the weak coupling regime, the force as a function of time is shown to be a superposition of force components that are related to the electronic density matrix elements at a chosen time. These force components depend on the position-dependent polarizability of the atom, which correctly accounts for the body-induced level shifts and broadenings.     

Deformation of the contact area and adhesive friction between a scanning frictional microscope probe and the atomic-flat surface

The determination of the equilibrium atomic structure of a nanotribocontact, formed by a hard probe to be viewed as a paraboloid of revolution and subjected to an external load, with the soft surface modeled by a set of parallel atomic planes is considered. Structural, energy, and load characteristics are calculated. In addition, dissipative static adhesive friction as a function of the normal load and the radius of probe curvature for the diamond-graphite system is derived. A number of approximations of the interatomic potentials is used. It is shown that an allowance for the deformation of the contact area causes the adhesive frictional force in the tensile (negative) load range to decrease. For positive loads in a range of 0–80 nN, the variation of the frictional force (when deformation is taken into account) depends on the radius of the probe curvature and the used approximation of the interaction potential. The dependence of friction on the radius of the probe curvature is close to a direct proportionality. The calculated results are compared with the available experimental data.