Determining calibration friction coefficient

We present a quantitative study of frictional properties of pure self-assembled monolayers (SAMs) of alkanethiols as a function of chain length and mixed SAMs of dodecanethiol and 11-mercapto-l-undecanol as a function of surface composition on Au (111) using atomic force/friction force microscopy (AFM/FFM). The lateral and normal forces were calibrated in situ using a combined two-slope and added-mass method. Molecular dynamics simulations were also carried out to interpret the chain length dependence of frictional properties of alkanethiols. We then extended the in situ force calibration method to the mixed SAMs and investigated the effects of chemical nature and relative humidity on the frictional properties. Friction coefficients were plotted as a function of surface composition with different relative humidity. Such a plot could serve as a reference in determining surface composition in a nanoscale domain by measuring its friction coefficient. 

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