Electric dipole image forces in three-layer systems: The classical electrostatic model

Electrostatic image force energy for charges in three-layer structures: exact formulas and their approximations

The problem of image force energyW(Z) in three-layer plane structures, whereZis the coordinate perpendicular to the layers, has been reconsidered. In the classical electrostatic limit, where the dielectric permittivitiesɛ_iof all structure components (i= 1, 2, 3) are constants, the exact general dependencesW(Z) were obtained for each layer and anyɛ_i-combination in terms of the Lerch transcendent function. For certain combinations ofɛ_i, an ion adsorption minimum was found to arise in one of the covers far from the interlayer. Some other combinations ofɛ_ican lead to the appearance of a potential barrier, which does not permit a free charge existing in the cover to approach the interlayer, although it will be attracted to the interlayer in the close vicinity of the latter. For symmetric structures (ɛ₁=ɛ₃), the asymptotic behavior ofW(Z→∞)was shown to beZ-2rather thanZ-1, as it takes place in the two-layer case. Simple approximate analytical formulas that describeW(Z) and possess high accuracy for arbitrary relationships among theɛ_i-constants were proposed.

Orientation of adsorbed polar molecules (dipoles) in external electrostatic field

A model is proposed in the framework of classical electrostatics to describe the behavior of an adsorbed polar molecule near the plane interface between two insulators under the action of an external electrostatic field. The molecule is considered as a permanent point dipole that polarizes the interface and interacts with it through electrostatic image forces. The latter and the applied field try to reorient the dipole in a competitive manner. The system behavior turns out to be rather complicated: it may show a bistable character with a hysteresis (a switch). Such a switch can serve as an element in a memory network made of adsorbed molecules.