The surface force apparatus (SFA) is a technique pioneered by D. Tabor, R.H.S. Winterton, J.N. Israelachvili in the early 1970s at Cambridge University. By the mid-70’s Israelachvili had adapted the original design to operate in liquids, notably aqueous solutions, while at the Australian National University.
In this instrument, two surfaces are carefully moved towards and retracted from one another, all the while measuring their interaction force. One surface is held by a cantilevered spring, and the deflection of the spring is used to calculate the force being exerted.
