AFMs

An atomic force microscope (AFM) is a type of scanning probe microscope that images surfaces at the nanometer scale by measuring forces between a sharp tip and the sample. The tip, attached to a flexible cantilever, interacts with the surface as the cantilever is raster-scanned over the area. A laser beam is reflected from the top surface of the cantilever onto a photodetector, and the resulting signal reports the cantilever deflection caused by tip-sample forces.

The deflection signal is fed to a feedback loop that adjusts the vertical position of the tip to maintain a chosen interaction, yielding a high-resolution map of surface topography. AFMs can operate in air, in liquids, or under controlled environments, and they do not require the sample to be electrically conductive.

Operating modes include contact mode, in which the tip remains in contact with the surface; non-contact mode, where the tip detects long-range forces while hovering above the surface; and tapping or dynamic mode, where the cantilever is oscillated near its resonance and the oscillation amplitude is kept constant. Each mode offers different trade-offs in terms of resolution, force applied, and damage risk to delicate samples.

Applications and variants are broad. AFMs provide high-resolution topography and can quantify mechanical properties through force-distance spectroscopy. Specialized forms include conductive AFM for electrical measurements, magnetic force microscopy for magnetic domains, and Kelvin probe force microscopy for surface potential. AFMs are widely used in materials science, biology, polymers, and semiconductor research, among other fields.

Historically, the AFM was developed in 1986 by Gerd Binnig, Calvin Quate, and Christoph Gerber as an evolution of scanning probe concepts that enables imaging of non-conductive samples with atomic-scale resolution.