Fundamental investigation of micro-scale wear characteristics of ultra-fine gold wires under low contact force and long sliding distance

Micro-scale wear characteristics of ultra-fine gold wires with a diameter of ~28μm was investigated under a low contact force over a long sliding distance up to ~200km. The tip of the wire was slid against a silicon wafer under a low normal force of 5μN. Wear of the gold wire was quantified from the images of the tip obtained by a 3D laser microscope and a scanning electron microscope before and after the wear test. The dimensionless Archard relationship wear coefficient was in the order of 10^-7 which was extremely low considering that sliding was carried out in dry condition. Such a low wear characteristics was attributed to low contact pressure that could be achieved by formation of a conformal contact due to flattening of the wire tip as sliding wear progressed. Wear behavior of the gold wire could be characterized by formation of thin flakes of wear debris that were generated as a result of adhesive shear stress imparted at the sliding interface. As an effort to reduce the wear coefficient even further, octadecyltrichlorosilane self-assembled monolayer was deposited on the silicon to serve as a nano-lubricant. It was effective in improving the wear resistance by about two-fold.