Contact adhesion between solids in vacuum. I. Single-asperity experiments

A new technique is described for measuring the adhesion between a sharply curved metal point (platinum, tungsten, titanium, nickel or gold, with a radius of curvature typically 300 nm) and a flat surface (platinum, tungsten, cobalt, silicon or graphite). Adhesion forces as small as 100 nN can be measured with a sensitivity (limited by friction and vibration) of 20 nN, and the electrical resistance of the contact region is measured as a function of positive and negative load. Any plastic deformation of the metal point, as well as its cleanliness, is monitored by current and voltage measurements on electrons drawn by field emission from the point before and after contact.