Avalanche in Adhesion at Metal Interfaces

Simulations have shown that as two metal surfaces approach each other, the surface layers can avalanche together when the rigid interfacial spacing falls below a critical distance. This is accompanied by a discontinuous decrease in the adhesive energy. Here we present an examination of this phenomenon for the body centered cubic (BCC) metals Fe and W using the Equivalent Crystal Theory. In order to identify the circumstances under which avalanche might be inhibited, the effect of loss of registry between the two surfaces is investigated in detail. The avalanche is inhibited when the two surfaces are sufficiently far out of registry and when only a few layers near the surface are allowed to relax. As the relaxing slabs get thicker a sharp avalanche reappears. However, as the loss of registry increases the energy released in the avalanche decreases

Interfacial adhesion: Theory and experiment

Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along wiith recommendations for future progress and needs

Resonant band-electron –f -electron scattering theory for highly correlated actinide systems

In earlier studies we recognized that the highly correlated behavior of the f electrons within moderately delocalized light actinide (uranium, neptunium, plutonium) systems is linked to the non-f-band behavior via the hybridization process. By transforming the hybridization into a bandelectron-f-electron resonant scattering from the correlated multiplet states of the actinide ions, and considering only the scattering processes that involve f electrons in the ml=0, ms=+/-1/2 states (for quantization along the interionic axis) which dominate the two-ion interactions, our earlier work explained the main features of the anisotropic magnetic equilibrium behavior for the PuSb system but failed to reproduce the correct polarization (longitudinal) for the long-period antiferromagnetic structure observed in the temperature range below the Neel temperature. In this paper we include the next-to-dominant scattering channels (single-site scattering processes involving f electrons with ml=+/-1, ms-/+1/2). This refinement changes the angular dependence of the anisotropic interaction, and successfully yields the ferromagnetic to longitudinally polarized long-period antiferromagnetic phase transition as is experimentally observed. Excellent agreement with experiment for the correlation length anisotropy is also obtained. For the magnetic excitation behavior in the ferromagnetic phase pertinent to PuSb at T=O, the theory gives a spectrum with two polarized branches at the zone boundary for q along the [100] (transverse-to-moment) direction. In fact, the predicted excitation behavior is rather remarkable. The appearance of two polarized branches rather than a single branch at the zone boundary occurs only over an extremely narrow range of crystal-field splitting. We choose the crystal-field splitting to give two branches, and this unadjustably yields excitation energies that are very close to the experimental values. An only slightly different crystal-field value would give neither two branches nor correct excitation energies