instrument

atomic force microscope

A microscope that maps surface topography by measuring forces between a sharp tip and the sample.
13 related articles

Description

An atomic force microscope (AFM) is a device that images surfaces at the nanoscale by physically 'feeling' them with an extremely sharp tip, rather than using light or electrons. The tip, mounted on a flexible cantilever, is scanned across the sample. As the tip approaches the surface, atomic forces (like van der Waals forces, electrostatic forces, or even chemical bonding) cause the cantilever to bend. By measuring this bending with a laser and photodetector, the AFM builds a topographical map of the surface with atomic resolution. It can work on conductors, insulators, and even living biological samples in liquid.

History

The AFM was invented in 1986 by Gerd Binnig, Calvin Quate, and Christoph Gerber, following Binnig's earlier invention of the scanning tunneling microscope (STM). It quickly became a workhorse in nanoscience because it could image non-conductive samples.

How it works

The AFM operates in several modes. In contact mode, the tip is dragged across the surface and the deflection is kept constant via a feedback loop. In tapping mode, the cantilever oscillates at its resonance frequency and the tip only lightly touches the surface, reducing damage. The key is the feedback system: a computer adjusts the height of the tip to maintain a constant force or amplitude, and the adjustments are recorded as the height profile. This allows the AFM to measure not just topography but also mechanical properties like stiffness and adhesion.

In practice

AFM is used in materials science to characterize thin films, in biology to image DNA and proteins, and in the semiconductor industry to inspect chip surfaces.

Fun fact

The sharpest AFM tips are so fine that they can end in a single atom, allowing researchers to image individual atoms and even manipulate them.

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Related articles · 13

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