MECHANICAL AND ELECTRICAL-PROPERTIES OF METALLIC CONTACTS AT THE NANOMETER-SCALE

In the first part we present computer simulations of the influence of a layer of foreign atoms on the force of adhesion between an asperity and substrate of the same metal. Regardless of whether or not wetting of the foreign layer by the tip occurs, it is found that the force of adhesion is always reduced relative to the case where no foreign layer is present. A simple liquid drop model is presented to explain this result. We then consider the electronic conductance of the system, in the absence of a foreign layer, as the asperity is brought into contact with the substrate and subsequently removed. The conductance is calculated by a quantum mechanical scheme using atomic positions generated by molecular dynamics. The conductance is found to change in jumps during contact formation and fracture, but the conductance per atom is not quantized. The jumps coincide with gross structural rearrangements resulting from mechanical instabilities in the system. Relevant experimental observations are mentioned.