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A quartz crystal microbalance and dissipation simultaneously measuring the frequency and the dissipation over more than one decade, from fundamental to overtone 15, is used to investigate the evaporation mechanisms of small water sessile droplets onto a gold surface. An unexpected weak increase in frequency is observed during the first stage of evaporation where the contact line is pinned while the dissipation is unchanged. The increase in frequency has a linear dependence with the overtone order so it is related to a very thin amount of water. A droplet deposited inside a circular barrier does not exhibit such a variation suggesting that the observed effect is related to the region in the vicinity of the edge of the droplet. [ABSTRACT FROM AUTHOR]

The generation of shear and compressional waves in liquids by AT-cut quartz crystals has received much attention in the past; however, this is not the case for droplets deposited onto quartz crystals. In this paper, we investigate the compressional wave generation in droplets and use different techniques to correlate the compressional wave generation to the shape of the droplets using frequency and dissipation measurements in an oscillator circuit while using a video camera to record the shape during evaporation. A good correlation between eigenmodes predicted by a finite element method and those obtained experimentally are observed. [ABSTRACT FROM AUTHOR]

In this work, we evaluate the influence of the cantilever width on the hydrodynamic drag force. To do so, we present an experimental analysis of the thermal motion in air and liquid of a commercial and modified by focused ion-beam (FIB) milling silicon nitride cantilevers. From the thermal noise spectrum, we extract the damping for different cantilever-sample distances. We show that the hydrodynamic force due to the drag can be reduced by almost an order of magnitude when reducing the cantilever width. With the FIB modification (milling) one can still use conventional atomic force microscope heads with a significant reduction of the hydrodynamic forces. [ABSTRACT FROM AUTHOR]

This article is a theoretical and a numerical investigation of the stability of a tip–cantilever system used in noncontact atomic force microscopy (NC-AFM) when it oscillates close to a surface. No additional dissipative force is considered. The theoretical approach is based on a variational method exploiting a coarse grained operation that gives the temporal dependence of the nonlinear coupled equations of motion in amplitude and phase of the oscillator. Stability criterions for the resonance peak are deduced and predict a stable behavior of the oscillator in the vicinity of the resonance. The numerical approach is based on results obtained with a virtual NC-AFM developed in our group. The effect of the size of the stable domain in phase is investigated. These results are in particularly good agreement with the theoretical predictions. They also show the influence of the phase shifter in the feedback loop and the way in which it can affect the damping signal. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the Tapping mode, a variation of the oscillation amplitude and phase as a function of the tip sample distance is the necessary measurement to access quantitatively to the properties of the surface. In the present work, we give a systematic comparison between experimental data recorded on two surfaces, phase and amplitude, and theoretical curves. With an interaction between the tip and the surface taking into account an attractive and a repulsive term, the analytical approach is unable to properly describe the relationship between the phase variation and the oscillation amplitude variation. When an additional dissipation term is involved, due to the attractive interaction between the tip and the surface, the model gives a good agreement with the recorded data. Particularly, the trends in the phase variations related to the noncontact situations have been found to be amenable to an analysis based upon a simple viscoelastic behavior of the surface. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the nonlinear dynamical properties of an oscillating tip-cantilever system in the tapping mode. Extraction of analytical expressions describing the tapping mode; Attractive interaction between the tip and the sample; Intermittent contact regime; Attractive and repulsive fields.

The theoretical and numerical investigation of the stability of a tip-cantilever system used in noncontact atomic force microscopy (NC-AFM) when it oscillates close to a surface is presented. The results show the contribution of the phase shifter in the feedback loop and the way it can lead to damping variations.