dynamic Atomic Force Microscopy methods

Abstract In this report we review the fundamentals, applications and future tendencies of dynamic Atomic Force Microscopy (AFM) methods. Our focus is on understanding why the changes observed in the dynamic properties of a vibrating tip that interacts with a surface make possible to obtain molecular resolution images of membrane proteins in aqueous solutions or to resolve Atomic-scale surface defects in ultra high vacuum (UHV). Our description of the two major dynamic AFM modes, amplitude modulation Atomic Force Microscopy (AM-AFM) and frequency modulation Atomic Force Microscopy (FM-AFM) emphasises their common points without ignoring the differences in experimental set-ups and operating conditions. Those differences are introduced by the different feedback parameters, oscillation amplitude in AM-AFM and frequency shift and excitation amplitude in FM-AFM, used to track the topography and composition of a surface. The theoretical analysis of AM-AFM (also known as tapping-mode) emphasises the coexistence, in many situations of interests, of two stable oscillation states, a low and high amplitude solution. The coexistence of those oscillation states is a consequence of the presence of attractive and repulsive components in the interaction Force and their non-linear dependence on the tip–surface separation. We show that key relevant experimental properties such as the lateral resolution, image contrast and sample deformation are highly dependent on the oscillation state chosen to operate the instrument. AM-AFM allows to obtain simultaneous topographic and compositional contrast in heterogeneous samples by recording the phase angle difference between the external excitation and the tip motion (phase imaging). Significant applications of AM-AFM such as high-resolution imaging of biomolecules and polymers, large-scale patterning of silicon surfaces, manipulation of single nanoparticles or the fabrication of single electron devices are also reviewed. FM-AFM (also called non-contact AFM—NC-AFM) has achieved the long-standing goal of true Atomic resolution with AFM in UHV. Our analysis starts with a discussion of the relation between frequency shifts and tip–surface interactions, emphasising the ability of perturbation theory to describe the measured frequency shift. We discuss the role of short-range chemical interactions in the Atomic contrast, with particular attention to semiconductor and ionic (alkali halides and oxides) surfaces. Also included is a detailed quantitative comparison between theoretical simulations and experiment. Inversion procedures, the determination of the tip–sample interaction from the frequency shift versus distance curves above specific sites, are also reviewed. We finish with a discussion of the optimal range of experimental operation parameters, and the use of damping (excitation amplitude) as a source of Atomic contrast, including the possible interpretation in terms of microscopic dissipation mechanisms.

Probing Nanometer Structures with Atomic Force Microscopy.

Atomic Force Microscopy (AFM) can generate high-resolution images of the surface of biological specimens and can also probe the interactions between and within single macromolecules. Thus isolated heterogeneous biological structures can be studied in submolecular detail with AFM.

RECENT ADVANCES IN BIOLOGICAL Atomic Force Microscopy

Recent developments in biological Atomic Force Microscopy are reviewed. In addition to the advances in methodology, new structural information of different biological systems revealed by the Atomic Force Microscopy is also presented. A discussion regarding the contrast, resolution and specimen deformation is provided based on a theoretical model.

Promises and problems of biological Atomic Force Microscopy

Summary

Recent developments in the biological applications of Atomic Force Microscopy are reviewed, and the great potential of this novel, high-resolution imaging technique, including its limitations and possible future directions for biological research, are discussed.

Characterization of Materials – Ultrasonic Atomic Force Microscopy

For the development of advanced electronic and mechanical devices on the micro- and nanoscale, there is an increasing need for the characterization of elasticity and subsurface defects. As a useful method, principle, implementation, and applications of ultrasonic Atomic Force Microscopy (UAFM) and related methods for elastic materials characterization are described. It measures the contact stiffness from the resonance frequency of cantilever with the tip in contact with the sample surface. We focus on the concept of effective enhancement of the cantilever stiffness caused by the inertia of a soft cantilever at or above the contact resonance frequency. By virtue of this effect, new findings on elasticity of materials were achieved by many groups so far. Relation between UAFM and ordinary Atomic Force Microscopy (AFM) is explained in detail. Also, lateral modulation Atomic Force Microscopy (LM-AFM) with application to nanotribology is explained.

Keywords:

Atomic Force Microscopy;
nanotechnology;
elasticity;
ultrasonics;
defects;
contact resonance;
contact stiffness;
graphene;
delamination

Ultrasonic Atomic Force Microscopy of Subsurface Defects

We show principle, implementation and remarkable applications of ultrasonic Atomic Force Microscopy (UAFM) to evaluation of components with scientific and technological importance. In particular, carbon fiber in CFRP, domain of ferroelectric PZT and subsurface delamination of electrodes in microdevices are shown. We also show lateral modulation Atomic Force Microscopy (LM-AFM) with application to a carbon nanotube composite and discuss its extension using combination with UAFM.