期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：50
页码：14213-14218
DOI：10.1073/pnas.1608792113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIntermolecular interactions are governed by complex energy landscapes that give rise to their kinetic behavior and nanoscale properties. These properties have been measured, but the underlying energy landscapes for many stable interactions have not, as soft springs are commonly unable to fully measure strong interactions. We used atomic force microscopy with a white-noise excited cantilever to overcome this challenge, observing highly adhesive silicon nitride-mica interactions in water, and reconstructing the interaction energy as a function of tip-sample distance. Confirming our method with established models, we found an ideal excitation energy that allowed the cantilever to explore the full depth and contour of the energy landscape, demonstrating a capability for directly measuring highly adhesive interactions. Free-energy landscapes govern the behavior of all interactions in the presence of thermal fluctuations in the fields of physical chemistry, materials sciences, and the biological sciences. From the energy landscape, critical information about an interaction, such as the reaction kinetic rates, bond lifetimes, and the presence of intermediate states, can be determined. Despite the importance of energy landscapes to understanding reaction mechanisms, most experiments do not directly measure energy landscapes, particularly for interactions with steep force gradients that lead to premature jump to contact of the probe and insufficient sampling of transition regions. Here we present an atomic force microscopy (AFM) approach for measuring energy landscapes that increases sampling of strongly adhesive interactions by using white-noise excitation to enhance the cantilevers thermal fluctuations. The enhanced fluctuations enable the recording of subtle deviations from a harmonic potential to accurately reconstruct interfacial energy landscapes with steep gradients. Comparing the measured energy landscape with adhesive force measurements reveals the existence of an optimal excitation voltage that enables the cantilever fluctuations to fully sample the shape and depth of the energy surface.
关键词：atomic force microscopy ; energy landscape ; interfacial energy ; stochastic excitation ; dynamic force spectroscopy
