Origins of phase contrast in the atomic force microscope in liquids

Author

• John Melcher, Purdue UniversityFollow
• Carolina Carrasco, Univ Autonoma Madrid
• Xianfan Xu, Birck Nanotechnology Center, School of Materials Engineering, Purdue UniversityFollow
• Jose L. Carrascosa, CSIC, Dept Estructura Macomol, Ctr Natl Biotecnol, E-28049 Madrid, Spain
• Julio Gomez-Herrero, Univ Autonoma Madrid
• Pedro Jose de Pablo, Univ Autonoma Madrid
• Arvind Raman, Birck Nanotechnology Center, School of Materials Engineering, Purdue UniversityFollow

Abstract

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.

Keywords

atomic force microscopy; liquid environments; energy dissipation; higher eigenmodes; momentary excitation

Date of this Version

8-2009

Recommended Citation

Melcher, John; Carrasco, Carolina; Xu, Xianfan; Carrascosa, Jose L.; Gomez-Herrero, Julio; Jose de Pablo, Pedro; and Raman, Arvind, "Origins of phase contrast in the atomic force microscope in liquids" (2009). Birck and NCN Publications. Paper 453.
https://docs.lib.purdue.edu/nanopub/453