Jean-Pierre Aimé

Hydrodynamics of oscillating atomic force microscopy cantilevers in viscous fluids

We present a study of thermal noise of commercially available atomic force microscopy (AFM) cantilevers in air and in water. The purpose of this work is to investigate the oscillation behavior of a clamped AFM microlever in liquids. Up to eight vibration modes are recorded. The experimental results are compared to theoretical predictions from the hydrodynamic functions corresponding to rigid transverse oscillations of an infinitely long rectangular beam. Except for the low-frequency modes, the known hydrodynamic functions cannot describe the amount of dissipated energy due to the liquid motion induced by the cantilever oscillation. The observed variation of the damping coefficient is smaller than the one predicted. The difference at higher modes between the mentioned theoretical description and experimental results is discussed with the help of numerical solutions of the three-dimensional Navier–Stokes equation.

Nonlinear dynamical properties of an oscillating tip–cantilever system in the tapping mode

The dynamical properties of an oscillating tip–cantilever system are now widely used in the field of scanning force microscopy. The aim of the present work is to get analytical expressions describing the nonlinear dynamical properties of the oscillator in noncontact and intermittent contact situations in the tapping mode. Three situations are investigated: the pure attractive interaction, the pure repulsive interaction, and a mixing of the two. The analytical solutions obtained allow general trends to be extracted: the noncontact and the intermittent contact show a very discriminate variation of the phase. Therefore the measurement of the phase becomes a simple way to identify whether or not the tip touches the surface during the oscillating period. It is also found that the key parameter governing the structure of the dynamical properties is the product of the quality factor by a reduced stiffness. In the attractive regime, the reduced stiffness is the ratio of an attractive effective stiffness and the c...

Tip's finite size effects on atomic force microscopy in the contact mode: simple geometrical considerations for rapid estimation of apex radius and tip angle based on the study of polystyrene latex balls

Abstract Atomic force microscopy (AFM) has been developed as a tool for investigating any type of surface at an atomic scale. Since then, except for particular surfaces exhibiting an atomic roughness, we know that the finite size of the tip does not allow us to access at the whole structure of the surface. Moreover, the tip geometry radically modifies the range of the interactions. Therefore, even an approximate knowledge of the tip geometry is of particular importance. The aim of the present note is to provide a simple way to get the main parameters of a tip — its apex radius of curvature and the cone angle — by using a simple reference sample: latex balls. To do so, simple geometrical arguments are used, assuming that both the tip and the sample behave like hard samples, a reasonable assumption at a mesoscopic scale (tens of nanometres to micrometres). Using this simplifying assumption, we present a formula which could be used to rapidly evaluate the effect of the finite size of the apex of the tip in the formation of AFM images of simple objects: steps, isolated spheres or two-dimensional close-packed lattices of spheres, and cosinusoidal corrugations. Two types of tip geometry are presupposed: a conic tip truncated by a spherical apex or a parabolic tip. It is then shown that, in practice, latex balls can be used as a reference to estimate the radius of curvature of the apex, and the angle of the cone.

NONLINEAR DYNAMIC BEHAVIOR OF AN OSCILLATING TIP-MICROLEVER SYSTEM AND CONTRAST AT THE ATOMIC SCALE

In this paper the dynamic behavior of an oscillating tip-microlever system at the proximity of a surface is discussed. We show that the nonlinear behavior of the oscillator is able to explain the high sensitivity of the oscillating tip microlever and the observed shifts of the resonance frequency as a function of the tip surface distance without the need of introducing a particular short range force.

Comments on the use of the force mode in atomic force microscopy for polymer films

Atomic force microscopy (A.F.M.) was first described as a powerful technique for studying insulating, hard surfaces. Since then, it has also been considered as an appropriate technique for investigating, at a submicromic scale, elastic and viscoelastic properties of soft materials as polymer films. An attempt is made to show how macroscopic models can be fruitfully employed in order to interpret the force curves obtained in AFM on polymer films. Through an analysis of the slope variation and the way the instability occurs at the tip‐sample contact, it is shown that a macroscopic approach is a useful way to explain most of the features of the force curves. Furthermore the importance is underlined of the initial conditions. It is shown that for polymer samples which have a stiffness within the range of the probe one, drastic changes of the force curve shape can occur when the initial conditions vary. Finally, this approach should allow one to clarify the conditions for which the macroscopic approach fails.

Characterization of dynamic cellular adhesion of osteoblasts using atomic force microscopy

Atomic force microscopy (AFM) can be used to visualize the cell morphology in an aqueous environment and in real time. It also allows the investigation of mechanical properties such as cell compliance as a function of cell attachment. This study characterized and evaluated osteoblast adhesion by AFM.

Hysteresis generated by attractive interaction: oscillating behavior of a vibrating tip–microlever system near a surface

We provide experimental evidence of hysteretic behavior of a vibrating microlever that arises when a surface approaches the microlever. An analytical solution is derived from a variational method that shows that the width of the hysteresis depends on the strength of the attractive interaction at a given driving amplitude. For a large attractive interaction, the hysteretic behavior disappears, and the oscillating amplitude of the microlever decreases as the tip is close to the surface without needing to touch the surface. As a direct consequence, the way the cycle of the hysteresis varies close to the surface can be used to measure the change in attractive interaction without disturbing the surface.

Improved acoustic excitation of atomic force microscope cantilevers in liquids

A simple modification of the existing setup used in the commercial atomic force microscopes (AFM) is presented with the aim of improving the piezoacoustic excitation in liquid used by the AFM community. The improvement removes the spurious peaks not corresponding to the resonance frequencies of the cantilever oscillation. To illustrate the benefits of such a clean excitation, very fine effects like the structuring of mesitylene confined between the oscillating AFM tip and a highly oriented pyrolitic graphite surface could be measured with subangstrom oscillation amplitudes and with very high accuracy.

Influence of noncontact dissipation in the tapping mode: Attempt to extract quantitative information on the surface properties with the local force probe method

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.

ELASTIC MISFIT STRESS-RELAXATION IN HIGHLY STRAINED INGAAS/GAAS STRUCTURES

The strain contrasts associated with three‐dimensional coherently strained islands formed during the epitaxial growth of highly strained In0.45Ga0.55As layers on GaAs (001) have been studied by transmission electron microscopy. It is demonstrated that the comparison of these experimental strain contrasts with simulated profiles makes it possible to assess the elastic relaxation of the islands.