Christoph Ernst Puts Together a Sub-$110 Atomic Force Microscope with Some Clever Component Choices

Maker Christoph Ernst has built an atomic force microscope for under $110 — by, where possible, using lower-cost components and upcycled alternatives to high-priced scientific hardware.

"An atomic force microscope is used to visualize the smallest surface structures by guiding a cantilever arm with a very thin and pointed tip on its underside over a sample to be examined," Ernst explains, in translation, of the device he set out to build. "In contact mode, the tip touches the surface. The cantilever arm also moves accordingly due to the smallest atomic unevenness."

In short: an atomic force microscope is not entirely dissimilar to a record player, where a pointed stylus "needle" makes physical contact with the record and amplifies tiny changes in the record's groove into audible sound. The biggest difference: atomic force microscopes work with surface changes far, far smaller than those of a record's groove — and they use lasers to do so.

In a traditional atomic force microscope, an atomically-fine stylus is attached to a cantilever underneath an angled laser. The laser light reflects into a detector, which can measure tiny changes in the reflection to infer the movement of the stylus tip ‒ and,thus, the shape of the surface the stylus is running across. Ernst's version work in the same way, but with a view to affordability rather than precision.

The sensor, in Ernst's case, is an ams OSRAM TSL1401 "linear sensor array" — effectively the answer to the question of what happens if you start building a digital camera's imaging sensor but stop after the first column. The sensor is made up of a single stripe of 128 photodiodes — lit up, for the homebrew atomic force microscope, by a cheap laser diode with a lens that projects a horizontal beam onto a mirror attached to the same cantilever system as the stylus.

That stylus? The needle from a pair of compasses. An XY stage, to move the sample underneath the stylus, is similarly thrifty, being made from stepper motors salvaged from old CD and DVD drives. A problem with the laser beam being too much for the TSL1401 to handle is solved with a cut-down piece of photographic filter, and the cantilever itself is a length of aluminum attached to a sturdy piece of box section steel.

A full write-up, in German, of the project — which delivers a tool capable of scanning surfaces with a resolution of around 9.83µm per pixel — is available on Ernst's website.