AFM investigation of tribological properties of nano-patterned silicon surface

The tribological properties of a nano-patterned Si surface have been investigated in ambient condition by atomic force microscopy (AFM). The pattern, consisting of parallel grooves, was realized on a Si(0 0 1) single crystal via focused ion beam (FIB) milling. The same technique was used to modify a commercial Si probe in order to obtain a flat tip, suitable for the tribological characterization of the patterned surface, since it presents an extended contact area. The dependence of the lateral force on the normal load has been studied, varying the sliding speed and the fast scan direction with respect to the pattern orientation. Lateral force versus normal load curves show a linear trend except in the region closed to the pull-off limit. In this region adhesive effects related to ambient condition strongly affect the process. This behavior is more evident on the pristine surface. Experimental results show that the friction coefficient is sensibly lower on the patterned area than on the unpatterned one. A non-negligible wear of the patterns related to the sliding of the flat tip has been detected.