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 cons tant of cantilevers used for lateral or friction measurements with the atom ic force microscope. The method simultaneously calibrates the photodiode re sponse to the angular deflection of the cantilever. It does not rely upon a ny approximate theory for friction, nor upon any simplified model cantileve r 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 typ e of cantilever, and the friction may subsequently be measured with any typ e of substrate or probe. (C) 2000 American Institute of Physics. [S0034-674 8(00)01507-0].