Frictional Dynamics at the Atomic Scale in Presence of Small Oscillations of the Sliding Surfaces

This chapter examines the effect of surface oscillations on frictional properties of surfaces by using an atomic force microscope (AFM). A diode laser was focused on the end of the cantilever and aligned to reflect the laser beam to the center of the detector. Proportional and integral gains of a feedback loop were set to low values because high values could exert a large influence on the lateral force measurement. The upper and lower curves represented trace and retrace in standard AFM measurements, respectively. Although the accurate amplitude of the vertical vibration was not measured at the high frequency, its amplitude-to-voltage parameter was about 1 nm/V at the low frequency, and the amplitude was linearly dependent on the applied voltage in the given frequency. The difference started to decrease even at a low driving voltage of 0.1 V and reached to an almost negligible value at 1 V. Different trends of frictional behavior might be observed for oscillation frequencies that are too close or much higher than the characteristic oscillation frequency defined by the AFM scanning velocity.