Calibrated measurement of the behaviour of mechanical junctions from micrometre to subnanometre scale: the friction force scanner

We describe an instrument called a friction force scanner (FFS) able to perform calibrated measurements of the behaviour of mechanical junctions with more than four orders of magnitude of resolution for both displacement and force. A probe carrier is suspended by fibres in an arrangement that provides exactly two degrees of freedom of motion. The suspension makes it possible to measure the carrier displacement by interferometry. A novel differential electrostatic actuator with linear response mounted on the carrier was used to precisely determine the force experienced by a junction. The single-stage design is easily calibrated and can be used for force measurement and scanning, allowing the study of friction at multiple length scales. Measurements involving mica–mica and steel–steel junctions are reported while using the instrument in open loop.