Origins of phase contrast in the atomic force microscope in liquids

John Melcher, Purdue University - Main Campus
Carolina Carrasco, Univ Autonoma Madrid
Xin Xu, Purdue University
Jose L. Carrascosa, CSIC, Inst Ciencia Mat Madrid
Julio Gomez-Herrero, Univ Autonoma Madrid
Pedro Jose de Pablo, Univ Autonoma Madrid
Arvind Raman, Purdue University

Date of this Version


This document has been peer-reviewed.



We study the physical origins of phase contrast in dynamic atomic force microscopy (dAFM) in liquids where low-stiffness microcantilever probes are often used for nanoscale imaging of soft biological samples with gentle forces. Under these conditions, we show that the phase contrast derives primarily from a unique energy flow channel that opens up in liquids due to the momentary excitation of higher eigenmodes. Contrary to the common assumption, phase-contrast images in liquids using soft microcantilevers are often maps of short-range conservative interactions, such as local elastic response, rather than tip-sample dissipation. The theory is used to demonstrate variations in local elasticity of purple membrane and bacteriophage phi 29 virions in buffer solutions using the phase- contrast images.


Engineering | Nanoscience and Nanotechnology