atomic force microscopy
/ uh-TOM-ik FORS my-KROS-koh-pee /
Picture a blind person reading the texture of a wall by sweeping a thin cane across it and feeling every gentle push-back. Atomic force microscopy works in much the same spirit: a tiny, springy arm with a sharp point at its tip glides over a surface, and the faint forces between the point and the surface tell us about every bump and dip far too small for the eye.
The springy arm is called a cantilever, like a microscopic diving board about as long as a human hair is wide. As its tip approaches the surface, atoms attract or repel it, and the cantilever bends ever so slightly; a laser beam bounced off its back amplifies this bending into a measurable signal. Often the cantilever is set vibrating, and the surface's pull changes how it vibrates. Scanning the tip across a grid and tracking these changes builds up a height map of the surface, point by point.
This matters because, unlike its cousin that reads tunneling current, it can feel forces on anything — metals, plastics, even living cells in water — so it works on insulators that other atomic-scale microscopes cannot touch. The honest caveat is that what you see is the tip's shape blurred together with the true surface: a tip that is too blunt smears fine detail, and pressing too hard can dent or drag soft samples, so the gentlest possible touch is the whole art.
Biologists use atomic force microscopy to trace the twisted shape of a single strand of DNA lying on a flat surface, gently dragging the tip across it to reveal a thread only about two billionths of a meter wide.
Feeling out a single DNA strand: the tip senses force, so even soft, non-conducting samples can be imaged.
Because it senses force rather than tunneling current, it does not need the sample to conduct electricity — the key difference from scanning tunneling microscopy. The two are siblings, but each suits different surfaces.