John Ferrante

Multilayer Relaxation and Surface Energies of FCC and BCC Metals Using Equivalent Crystal Theory

Abstract The multilayer relaxation of fcc and bcc metal surfaces is calculated using equivalent crystal theory. The results for changes in interplanar spacings of planes close to the surface and the ensuing surface energies are discussed in reference to other theoretical results and compared to available experimental data. The calculation includes high-index surfaces for which no other theoretical results are known.

A theory of adhesion at a bimetallic interface - Overlap effects.

Abstract A preliminary calculation of the chemical bonding adhesive interaction between metal surfaces is provided. In this first theory the Hohenberg and Kohn formalism is used to give the bimetallic adhesive binding energy versus separation. The close-packed planes of Al, Mg, and Zn are considered. The effect of simple overlap of the metal-vacuum distributions is determined. The importance of registry between contact surfaces is ascertained. A minimum in the binding energy curve is exhibited for all combinations. The theoretical predictions agree with trends in bond strengths taken from available experimental data. An insight into the mechanisms involved in metallic transfer is given. The relationship between dhesive energies, cohesive energies, and surface energies is discussed.

Heat of segregation of single substitutional impurities

The method of Bozzolo, Ferrante and Smith (BFS) is applied for the calculation of the heat of segregation of single substitutional impurities in fcc metals. A simple equation for predicting the heat of segregation is derived for the rigid case (no atomic relaxations). The results of including atomic relaxation using a Monte Carlo method are also presented and the results compared with a number of experimental and theoretical results.

Multilayer relaxation and surface structure of ordered alloys

Using BFS, a new semiempirical method for alloys, we study the surface structure of fcc ordered binary alloys in the L12 structure (Ni3Al and Cu3Au). We show that the surface energy is lowest for the mixed-composition truncation of the low-index faces of such systems. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.

Production of Ne Auger electrons by Ne/+/ bombardment of Mg and Al surfaces

A description is given of experiments which provide evidence for the production of an inner shell vacancy in the Ne by the asymmetric Ne-Mg and Ne-Al collision. In addition, autoionization states of neutral Ne have been observed. These states are to be distinguished from the more usual case in Auger electron spectroscopy of de-excitation of an ion with a core vacancy. The experiments involved the bombardment of Mg and Al surfaces with Ne(+) ions. A LEED-Auger system equipped with an ion gun and a four-grid retarding potential analyzer operated in the usual dN(E)/dE mode was used.

Universal behavior in ideal slip

The slip energies and stresses are computed for defect-free crystals of Ni, Cu, Ag, and Al using the many-atom approach. A simple analytical expression for the slip energies is obtained, leading to a universal form for slip, with the energy scaled by the surface energy and displacement scaled by the lattice constant. Maximum stresses are found to be somewhat larger than but comparable with experimentally determined maximum whisker strengths.

Universal aspects of adhesion and atomic force microscopy

Adhesive energies are computed for flat and atomically sharp tips as a function of the normal distance to the substrate. The dependence of binding energies on tip shape is investigated. The magnitudes of the binding energies for the atomic force microscope are found to depend sensitively on tip material, tip shape and the sample site being probed. The form of the energy-distance curve, however, is universal and independent of these variables, including tip shape.

Bulk properties of Ni3Al (??) with Cu and Au additions

SummaryThe BFS method for alloys is applied to the study of 200 alloys obtained from addition of Cu and An impurities to an Ni3Al matrix. We analyze the trends in the bulk properties of these alloys (heat of formation, lattice parameter and bulk modulus) and detect specific alloy compositions for which these quantities have particular values. A detailed analysis of the atomic interactions that lead to the preferred ordering patterns is presented. The results, as well as the methodology presented, could be useful for examining transitory, metastable phases and the kinetics of precipitation.

Modelling of surfaces. I. Monatomic metallic surfaces using equivalent crystal theory

SummaryWe present a detailed description of equivalent crystal theory, focusing on its application to the study of surface structure. While the emphasis is on the structure of the algorithm and its computational aspects, we also present a comprehensive discussion on the calculation of surface energies of metallic systems with equivalent crystal theory and other approaches. Our results are compared to experiment and other semi-empirical as well as first-principles calculations for a variety of fcc and bec metals.

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.