Size dependent transitions in nanoscale dissipation

The irreversible loss of energy that occurs when a nanoscale tip vibrates over a surface can be monitored and quantified in amplitude modulation atomic force microscopy (AM AFM). Furthermore, two distinct dissipative processes can be identified and related to viscous and hysteretic forces respectively. Here, experimental evidence of a transition from viscous to hysteretic prevalent dissipation during mechanical contact is provided as the size of the tip increases from a few nm to 10 nm or more. Long range dissipation, defined as distances for which mechanical contact does not occur, is also investigated and related to capillary interactions. Experiments conducted on freshly cleaved mica samples show that energy dissipation increases with tip size and relative humidity in the long-range before mechanical contact occurs. Long- and short-range interactions are discussed in terms of observables both experimentally and by numerically integrating the equation of motion.