Capillary forces in tapping mode atomic force microscopy

Abstract

We investigated the influence of the relative humidity on amplitude and phase of the cantilever oscillation while operating an atomic force microscope (AFM) in the tapping mode. If the free oscillation amplitude A0 exceeds a certain critical amplitude Ac, the amplitude- and phase-distance curves show a transition from a regime with a net attractive force between tip and sample to a net repulsive regime. For hydrophilic tip and sample this critical amplitude Ac is found to increase with increasing relative humidity. In contrast, no such dependence was found for hydrophobic samples. Numerical simulations show that this behavior can be explained by assuming the intermittent formation and rupture of a capillary neck in each oscillation cycle of the AFM cantilever

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

“…This is reminiscent of AFM force curves in air where there is a strong 70 attractive interaction between the tip and the substrate due to capillary forces. 47,48 During this pull-off period, there was a small decrease in the limiting current, which might be a consequence of a small decrease in the contact area of the meniscus with the surface. For the present studies, up to about one hour could elapse 5 between preparing the sample (albeit with protection from the electrolyte for part of the time) and finally landing the meniscus for SECCM imaging.…”

The 2/3 Power Law Dependence of Capillary Force on Normal Load in Nanoscopic Friction

“…1 From a technological point of view, the reliability of hard disks, aerospace components, and miniature motors depends on the ability to control surface forces such as friction and capillary forces at the microdown to the nanoscale. 2,3 Atomic force microscopy (AFM) has become a powerful technique to study surface forces at the nanoscale, [4][5][6][7][8] and the AFM tip sliding on a surface can often be considered as a model system for technologically relevant devices.…”

Formation and Evolution of A Confined Liquid Condensate at the Crack Tip in Glasses

“…An increase of dissipative interaction between the tip and the surface will thus corresponds in both modes to a phase closer to -90° (which means an increase of the phase in "non-contact" mode and a decrease of the phase in "intermittent contact mode). The interactions leading to the predominance of one or the others of these modes are not yet well-established, but the influence of relative humidity has been shown by several experiments 15,18 . Under normal conditions of temperature and pressure, even at very low relative humidity (below 1%), silica glass and silicon tips are covered by a few layers of water molecules 19,20 (layer thickness around 0.5 nm).…”

“…One of the main difficulties lays in the existence of multi-stable solutions for the response of the oscillator. These multi-stabilities have been frequently documented to explain the hysteresis commonly observed in amplitude-and phasedistance curves [13][14][15] . Typically, two stable modes of oscillation can be observed which corresponds to different interactions between the tip and the surface.…”

“…In the second mode, called "intermittent contact" mode, the tip comes closer to the surface and feels both the attractive forces and the repulsive forces. Figure 2 represents two theoretical typical amplitude-and phase-distance curves [13][14][15][16] for a driven frequency chosen below the resonant frequency (ω<ω 0 ). Solid line curve corresponds to a pure "non contact" mode and dashed line curve to the transition between a "non-contact" and an "intermittent contact" mode.…”