Calibration of the torsional spring constant and the lateral photodiode response of frictional force microscopes

We present a direct one-step technique to measure the torsional spring constant of cantilevers used for lateral or friction measurements with the atomic force microscope. The method simultaneously calibrates the photodiode response to the angular deflection of the cantilever. It does not rely upon any approximate theory for friction, nor upon any simplified model cantilever geometry or elasticity. The technique is verified by comparison with the calculated spring constant and with an independent measurement of the angle calibration. This nondestructive calibration may be performed with any type of cantilever, and the friction may subsequently be measured with any type of substrate or probe.