Atomic Force Microscopy in Solid Mechanics
Scanning probe microscopes (SPMs) have become a key instrument for the application and sensing of nanonewton forces in small material volumes and the measurement of in-plane and out-of-plane strains with nanometer resolution. The versatility of SPMs lies
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Atomic Force
17. Atomic Force Microscopy in Solid Mechanics
Ioannis Chasiotis
Scanning probe microscopes (SPMs) have become a key instrument for the application and sensing of nanonewton forces in small material volumes and the measurement of in-plane and out-ofplane strains with nanometer resolution. The versatility of SPMs lies with the ability to specify the nature of tip-material interaction forces in order to probe relevant nanoscale phenomena or control the position of individual atoms and molecules that is not possible by other highresolution imaging instruments. As a result, new capabilities in nanoscale experimentation and mechanics of materials at the nanometer scale have emerged along with new challenges and opportunities for further developments. It is the objective of this chapter to introduce the new as well as the advanced SPM user to the underlying operating principles, the advantages, and the limitations of SPMs.
17.2 Instrumentation for Atomic Force Microscopy................... 17.2.1 AFM Cantilever and Tip.................. 17.2.2 Calibration of Cantilever Stiffness ... 17.2.3 Tip Imaging Artifacts ..................... 17.2.4 Piezoelectric Actuator ................... 17.2.5 PZT Actuator Nonlinearities ............ 17.3 Imaging Modes by an Atomic Force Microscope .............. 17.3.1 Contact AFM................................. 17.3.2 Non-Contact and Intermittent Contact AFM ........ 17.3.3 Phase Imaging ............................. 17.3.4 Atomic Resolution by an AFM .........
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17.4 Quantitative Measurements in Solid Mechanics with an AFM ............. 432 17.4.1 Force-Displacement Curves............ 432 17.4.2 Full Field Strain Measurements by an AFM ................................... 434 17.5 Closing Remarks ................................... 438 17.6 Bibliography ........................................ 439 References .................................................. 440
The term scanning probe microscopy (SPM) engulfs methods that utilize force interactions or tunneling current flow between a probe and a surface to construct a mapping of the geometric and material properties of the sample surface. The two most common methods are scanning tunneling microscopy (STM) [17.1] and atomic force microscopy (AFM) [17.2] that use a sharp tip to measure the tunneling current and the tip–sample force interactions, respectively. The latter are either short range (quantum mechanical, electrostatic) or long range (van der Waals), such as magnetic and electrostatic forces. Because the distance dependence of these forces is very strong, Angstrom-scale tip–sample separations can be detected and be translated into equivalent imaging resolution. Furthermore, local force interac-
tions can be used for spectroscopic analyses: the spatial distribution of various forces may be employed to construct an image of the surface and potentially its spatial composition. Along the same lines, optical information can be obtained by using near-field scanning optical mic
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