Molecular and Nanoscale Compositional Contrast of Soft Matter in Liquid: Interplay Between Elastic and Dissipative Interactions

We demonstrate that the phase contrast observed with an amplitude modulation atomic force microscope depends on two factors, the generation of higher harmonics components and the energy dissipated on the sample surface. Those factors are ultimately related to the chemical composition and structure of the surface. Our findings are general, but they specifically describe the results obtained while imaging soft materials in liquid. Molecular resolution experiments performed on a protein membrane surface in liquid confirm the theory.This work was supported by the Spanish Ministry of Science (MICINN) through Grants CSD2010-00024 and MAT2009-08650. J.R.R. has a JAE-Predoc fellowship from the European Social fund.Peer reviewe