Measurement of forces during the modification of C60 islands

A UHV atomic force microscope with a conducting tip is used to measure the tip-sample conductance as a function of the applied force on well-ordered, monolayer islands of C60 on Cu(111). By imaging the sample before and after each force-distance experiment, it was possible to investigate the forces required for the removal of individual C60 molecules from the islands. The removal of C60 occurs near defects or edges of the C60 islands and requires an applied force of 5-20 nN, which corresponds to applied pressures of ord er 1 GPa. In addition, it was possible to investigate the strength of the C 60 film on the molecular scale. It was found that the mechanical stiffness of a C60 molecule is of order 6 N/m and the islands appear to undergo a rev ersible yield process at an applied pressure of around 1.2 GPa. (C) 1999 El sevier Science B.V. All rights reserved.