INFLUENCE OF FRICTIONAL FORCES ON ATOMIC-FORCE MICROSCOPE IMAGES

In this work we simultaneously measure both the friction and applied force acting during imaging on graphite with an atomic force microscope (AFM), We show that: (i) The scan direction with respect to the cantilever is important for imaging at atomic resolution. (ii) In order to minimise the forces acting on the tip it may not be sufficient to simply reduce the applied force because if strong adhesive forces are present then both the friction forces and the contact area may be significant even at zero applied load. (iii) Adhesive forces may also influence the imaging of adsorbates which are only weakly bound to the substrate. At low scanning speeds in air adsorbed material tends to be dragged along by the tip whereas at higher speeds the adsorbates remain fixed. (iv) The friction data suggest that very high shear forces (approximately 1 GPa) can be sustained at the tip-sample contact.