The emergence of multifrequency force microscopy

Atomic force microscopy uses the deflection of a cantilever with a sharp tip to examine surfaces, and conventional dynamic force microscopy involves the excitation and detection of a single frequency component of the tip’s motion. Information about the properties of a sample is, however, encoded in the motion of the probe and the dynamics of the cantilever are highly nonlinear. Therefore, information included in the other frequency components is irreversibly lost. Multifrequency force microscopy involves the excitation and/or detection of several frequencies of the probe’s oscillation, and has the potential to overcome limitations in spatial resolution and acquisition times of conventional force microscopes. It could also provide new applications in fields such as energy storage and nanomedicine. Here we review the development of multifrequency force microscopy methods, highlighting the five most prominent approaches. We also examine the range of applications offered by the technique, which include mapping the flexibility of proteins, imaging the mechanical vibrations of carbonbased resonators, mapping ion diffusion, and imaging the subsurface of cells.We are grateful for financial support from the Ministerio de Ciencia e Innovación (CSD2010-00024, MAT2009-08650).Peer reviewe

Image calculations with a numerical frequency-modulation atomic force microscope

cited By 6International audienceWe investigated the implementation of a numerical tool able to mimic an experimental noncontact atomic force microscope (nc-AFM). Main parts of an experimental setup are modeled and are implemented inside a computer code. The goal was to build a numerical AFM (n-AFM) as versatile, efficient, and powerful as possible. In particular, the n-AFM can be used in the two working regimes, that is, in attractive and repulsive regimes, with settings for a standard AFM cantilever oscillating with a large amplitude (typically, 10 nm) or for a tuning-fork probe with ultrasmall amplitudes (∼0.01 nm). We present various tests to show the reliability of the n-AFM used as a frequency-modulation AFM (FM-AFM). As an example, we calculated FM-AFM images of adsorbed molecular systems, which range from two-dimensional planar molecules to corrugated systems with a three-dimensional molecule. The submolecular resolution of the FM-AFM is confirmed to originate from repulsive Pauli-like interactions between the tip and the sample. The versatility of the n-AFM is finally discussed in the perspective of new functionalities that will be included in the future