Frictional behavior of Ag nanodot-pattern fabricated by thermal dewetting

The frictional behavior of a Ag nanodot-pattern fabricated on a silicon substrate by the thermal dewetting process was investigated. The motivation was to decrease the micro/nano-scale friction of thin films by utilizing nano-patterns to control the real contact area. A Ag thin film of 20 nm in thickness was initially deposited on a silicon wafer by RF sputtering. Then, a thermal dewetting process was carried out at annealing temperatures ranging from 250 to 550 °C in order to fabricate patterns with different morphologies. As a result, hemispherical shaped Ag nanodot-patterns could be fabricated on the silicon wafer. Friction tests were performed using an atomic force microscope (AFM) with a 44 μm diameter micro-sphere attached to the tip of the cantilever. Both initial and steady state frictional forces were measured. It was found that the frictional force of nanodot-patterned specimens was significantly lower than that of the smooth Ag film. Moreover, there was an optimum annealing temperature that resulted in the lowest friction coefficient. The effect of contact area on the frictional force was also assessed based on the experimental results and contact analysis.