CHARACTERIZATION OF ATOMIC-FORCE MICROSCOPE TIPS BY ADHESION FORCE MEASUREMENTS

The resolution limit in an atomic force microscope image usually is at tributed to the finite radius of the contacting probe. Here, it is sho wn that this assumption is valid only when adhesion forces are minimal . Relative to the tip-imposed geometrical limit, the resolution and co ntrast in AFM images can be degraded by increasing adhesion forces. Th e large adhesion forces observed for some tips at low humidity conditi ons are shown to be due to tip contamination or poorly formed tip apex es. Methods to determine and to reduce the extent of tip contamination are described. Cleaning carried out using UV-ozone or oxygen-plasma e tching were found to significantly reduce the minimum adhesion force.