Scanning Probe Studies of Nanoscale Adhesion Between Solids in the Presence of Liquids and Monolayer Films
Adhesion between solids is a ubiquitous phenomenon whose importance is magnified at the micrometer and nanometer scales, where the surface-to-volume ratio diverges as we approach the single atom.
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Scanning Prob 19.1 The Importance of Adhesion at the Nanoscale .................................. 605 19.2 Techniques for Measuring Adhesion ....... 606 19.3 Calibration of Forces, Displacements, and Tips .............................................. 19.3.1 Force Calibration .......................... 19.3.2 Probe Tip Characterization............. 19.3.3 Displacement Calibration .............. 19.4 The Effect of Liquid Capillaries on Adhesion......................................... 19.4.1 Theoretical Background ................ 19.4.2 Experimental and Theoretical Studies of Capillary Formation with Scanning Probes ................... 19.4.3 Future Directions.......................... 19.5 Self-Assembled Monolayers ................... 19.5.1 Adhesion at SAM Interfaces............ 19.5.2 Chemical Force Microscopy: General Methodology ................... 19.5.3 Adhesion at SAM-Modified Surfaces in Liquids.................................... 19.5.4 Impact of Intra- and Inter-Chain Interactions on Adhesion .............. 19.5.5 Adhesion at the Single-Bond Level. 19.5.6 Future Directions..........................
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19.6 Concluding Remarks ............................. 624 References .................................................. 624
methodologies, coupled with accurate theoretical modeling, are required to adequately tackle these complex measurements.
19.1 The Importance of Adhesion at the Nanoscale The mutual attraction and bonding of two surfaces, which can occur with or without an intervening medium, is a commonly observed phenomenon with far-reaching manifestations and applications in society. The ad-
herence between a raindrop and a window pane, the climbing of a gecko up a vine, the sticking of multiple adhesive note pads to a professor’s wall, the force required to separate hook-and-eye (VelcroTM ) strips, the building
Part C 19
Adhesion between solids is a ubiquitous phenomenon whose importance is magnified at the micrometer and nanometer scales, where the surface-to-volume ratio diverges as we approach the single atom. Numerous techniques for measuring adhesion at the atomic scale have been developed. Yet significant limitations exist. Instrumental improvements and reliable quantification are still needed. Recent studies have highlighted the unique and important effect of liquid capillaries, particularly water, at the nanometer scale. The results demonstrate that macroscopic considerations of classic meniscus theory must be, at the very least, corrected to take into account new scaling and geometric relationships unique to the nanometer scale. More generally, a molecular-scale description of wetting and capillary condensation as it applies to nanometerscale interfaces is clearly desirable, but remains an important challenge. The measurement of adhesion between self-assembled monolayers has proven to be a reliable means for probing the influence of surface chemistry and local environment on adhesion. To date, however, few systems have been in
