Adhesion and friction force measurements in ambient and high vacuum conditions

Physical insight into the frictional behaviour of surfaces in contact with vacuum and other special environments is important for the accuracy of positioning mechanisms operating in these environments. The positioning accuracy and drift in these mechanisms are strongly influenced by the frictional behaviour of the mating materials. The cause for both drift and positioning accuracy is stick-to-slip and slip-to-stick transitions at asperity level, resulting in a displacement at macrolevel. Adhesion as well as friction experiments were performed for single asperity and multi-asperity contacts both in ambient and high vacuum conditions on a novel designed vacuum-based adhesion and friction tester. This paper discusses the experimental setup designed and manufactured to investigate the adhesion and friction behaviour of a single asperity contact. The intrinsic roughness of the ball and the flat will form a multi-asperity contact. Pull-off and friction force measurements can be performed with the resolution better than 5 μN. The maximum normal load that can be applied with this system is 100 mN. The setup is capable of working at 10^-6 mbar vacuum level as well as in ambient conditions. Experimental results show that the surrounding environment and roughness play an important role both in the adhesion force and friction force measurements. The friction force measurements show good agreement with the basic theories of contact mechanics.