Separating different contributions to the shear force in near-field microscopy

The sheer force between a gold and a graphite sample and an approaching nea r-field optical probe using tuning fork detection is studied in detail. The adiabatic and dissipative contributions are clearly distinguished by monit oring the amplitude as well as the phase of the tip vibration when approach ing the surfaces. Their relative strengths vary differently but characteris tically with the distance. The interaction starts in case of graphite at a much larger distance. The adiabatic contribution is larger in the case of g old, whereas graphite shows mostly dissipative interaction. Measurements at various temperatures are performed using a gold sample, showing a dependen ce of the shear force on the temperature.