Characterized Metal Microcontacts

Abstract This paper describes a study of the contact between a fine tungsten point and a flat single crystal of nickel over a load range of approximately 1 to 1000/JN. The experiments are carried out in an ultrahigh vacuum (10−10 torr) scanning electron microscope with an Auger facility for characterising the nickel surface in situ. Electrical resistance measurements provide a reasonable estimate of the area of contact both on loading and unloading. The results show that even for zero joining load finite adhesion is observed, the unloading involving plastic deformation. A partial monolayer of oxygen has no effect on the adhesion: one or two monolayers produce some reduction: an oxide film about 5 nm thick produces a marked reduction in adhesion until, at a critical load, the oxide is penetrated. The results are discussed in terms of surface energy, ductility and fracture mechanics.