Quantitative Determination of Friction Coefficients by Friction Force Microscopy

A new way of obtaining absolute friction coefficients using the friction force microscope is presented. For microfabricated cantilevers it is very difficult to calculate reliable torsion and normal spring constants; both the shear and the Young's modulus are not well known. Their ratio, however, is constant and close to the bulk value. This fact is used to obtain quantitatively reliable friction coefficients. Furthermore, a new calibration method for the friction-signal detector is introduced. The measured friction coefficients for a silicon-nitride tip on mica, silicon and glass are: 0.071, 0.20 and 0.23. Occasionally non-linear effects, indicating possible single-asperity friction, were observed.