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Atomic Force Microscopy (AFM) is a form of scanning probe microscopy where a small probe is scanned across the sample to obtain information about the sample's surface. The information gathered from the probe's interaction with the surface can be as simple as physical topography or as diverse as the material's physical properties, magnetic properties, or chemical properties. These data are collected as the probe is raster-scanned across the sample to form a map of the measured property relative to the X-Y position. Thus, a microscopic image showing the variation in the measured property, e.g. height or magnetic domains, is obtained for the area imaged. The AFM probe has a very sharp tip, often less than 100 in diameter, at the end of a small cantilever beam. The probe is attached to a piezoelectric scanner tube, which scans the probe across a selected area of the sample surface. Interatomic forces between the probe tip and the sample surface cause the cantilever to deflect as the sample's surface topography (or other properties) changes. A laser light reflected from the back of the cantilever measures the deflection of the cantilever, and this information is fed back to a computer, which generates a map of topography and/or other properties of interest. Areas as large as about 100 m square to less than 100 nm square can be imaged. |
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To view more examples, go to the AFM Example Page. |
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Contact Mode - Topographical information with lateral resolution of <1nm and height resolution of less than 1Å. Lateral force mode measures relative frictional forces for the surface.
Intermittent Contact (Tapping Mode) AFM - Accurate topographical information even for very fragile surfaces - 50Å lateral and <1Å height resolution. Phase mode detects local changes in material physical properties. Images for magnetic domains and local electric fields are also obtained in this mode.
Lateral Force Microscopy - Measures the lateral deflection of the probe cantilever as the tip is scanned across the sample in contact mode. Changes in lateral deflection represent relative frictional forces between the probe tip and the sample surface.
Phase Detection Microscopy - With the system operating in Tapping mode, the cantilever oscillation is damped by interaction with the sample surface. The phase lag between the drive signal and actual cantilever oscillation is monitored. Changes in the phase lag indicate variations in the surface properties, such as viscoelasticity or mechanical properties. A phase image, typically collected simultaneously with a topographical image, maps the local changes in material physical or mechanical properties.
Magnetic Force Microscopy - This mode images local variations in the magnetic forces at the sample surface. The probe tip is coated with a thin film of ferromagnetic material that will react to the magnetic domains on the sample surface. The magnetic forces between the tip and the sample are measured by monitoring cantilever deflection while the probe is scanned at a constant height above the surface. A map of the forces shows the natural or applied magnetic domain structure of the sample.
Image Analysis - Since the images are collected in digital format, a wide variety of image manipulations are available for AFM data. Quantitative topographical information, such as lateral spacing, step height, and surface roughness are readily obtained. Images can be presented as two-dimensional or three-dimensional representations in hard copy or digital image files for electronic transfer and publication.
Nanoindentation - Quantitative measure of the material's mechanical properties in regions as small as a few nanometers. See also the separate section on Nanoindentation in the Handbook. |
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