Dynamical effective potential felt by an electron tunneling in the planar metal-insulator-metal system is considered. The tunneling electron coupled to the surface-plasmon modes is described within Feynman s path-integral formalism. Self-consistent numerical results for the effective potentials, tunneling times, and tunneling rates are presented. The classical image potential is obtained in the limit of long tunneling times. It is shown that in cases when the traversal time T becomes comparable to the plasmon, i.e. , screening time cu, , considerable departure from the classical image potential appears.

Experiments on surface melting of several organic materials have shown contradictory results. We study the Van der Waals interactions between interfaces in surface melting of the bulk CH 4 and interfacial melting of the CH 4 film on the M gO substrate. This analysis is based on the theory of Dzyaloshinskii, Lifshitz, and Pitaevskii for dispersion forces in materials characterized by the frequency dependent dielectric functions. These functions for magnesium oxide and methane are obtained from optical data using an oscillator model of the dielectric response. The results show that a repulsive interaction between the solid-liquid and liquid-vapor interfaces exists for the bulk methane. We also found that the van der Waals forces between two solid-liquid interfaces are attractive for the CH 4 film on the M gO substrate. This implies that the van der Waals forces induce the presence of complete surface melting for the bulk methane and the absence of interfacial melting for CH 4 on the MgO substrate.