Apparent hardening of soft samples through Q factor change in AFM

This experimental work aims to show that the Q factor value is an experimental parameter of great importance to access different soft materials properties with a dynamic Atomic Force Microscope. Two dynamic modes have been compared, amplitude modulation, usually called Tapping mode, and the frequency modulation mode. With Tapping, at low or intermediate Q values, the images mostly contain mechanical information. At very high Q values, more than 104, obtained in a vacuum, the experiments performed on a polyisoprene sample show that a pure topographic image can be recorded with Tapping, but not with frequency modulation. For large enough Q values, even on a very soft sample, images in which only topographic information is revealed can be obtained and are in agreement with theoretical predictions.