AVS 53rd International Symposium
    Nanometer-scale Science and Technology Monday Sessions
       Session NS-MoA

Paper NS-MoA1
Induced Water Condensation and Bridge Formation by Electric Fields in Atomic Force Microscopy

Monday, November 13, 2006, 2:00 pm, Room 2016

Session: Nanoscale Structures and Characterization I
Presenter: G.M. Sacha, Lawrence Berkeley National Laboratory
Authors: G.M. Sacha, Lawrence Berkeley National Laboratory
A. Verdaguer, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
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The formation of nanometer-sized water bridges between an Atomic Force Microscope (AFM) tip and a sample is a phenomenon that has produced a great interest in the last years. New applications in imaging and nanofabrication have driven efforts to understand nanometer-size capillarity. Water bridges play also an important role in contacts between objects, where it affects friction and energy dissipation. The interest in the topic has spurned theoretical efforts to model different aspects of capillarity meniscus formation.@footnote 1@ Most models are based on macroscopic approximations, molecular level grand canonical Monte Carlo Simulations and Density Functional Theory, all of them involving substantial computational effort.@footnote 2@ We have developed a simple analytical expression that can be used to determine in a quantitative way the presence and shape of the water film that forms between tip and sample in humid environments. This film grows under the influence of the electric field forming a meniscus that becomes unstable when a critical field is reached, at which point it suddenly forms a bridge between tip and surface. In AFM the capillary force bends the lever, which for small spring constants can bring the tip in contact with the surface. This is observed experimentally as a sudden jump-to-contact. Our approximation allows us to determine the distance and the voltage at which this capillary jump takes place. Apart from providing a simple way to calculate the critical field and distance it improves our understanding of the mechanisms of water induced jump-to-contact. Understanding and predicting water bridge formation is important for many applications and has implications in other physical processes including friction and adhesion in humid environments. @FootnoteText@ @footnote 1@ Gomez-Moñivas, S.; Sáenz, J.J.; Calleja, M. and Garcia, R. Phys. Rev. Lett. 2003, 91, 56101.@footnote 2@ Paramonov P. V. and Lyuksyutov S. F. J. Chem. Phys. 2005, 123, 084705.