Scanning Tunneling Microscopes are devices that allow you to image atomic scale features, commonly used in physics and semiconductor research. It was developed in 1981 by Gerd Binnig and Heinrich Rohrer, winning them a nobel prize.
A small handful of hobbyists have constructed DIY versions of these devices that would typically cost upwards of $30,000 (https://dberard.com/home-built-stm/, http://www.e-basteln.de/index.htm ). Our goal was to replicate this work within the timeframe of a hackathon, a feat that we believe to be the fastest construction to date.
How it Works
Atoms are small. Imaging atoms requires a probe equally as small. Ideally a probe is perfectly sharp and comes down to one atom, and we were able to create a probe close to that. We sweep the probe across the surface, and as it moves, electrons teleport from the probe into the surface for reasons not entirely understood. We measure the current, the rate of electrons leaving the probe, for each position on the surface. Higher currents (more atomic nuclei) make a brighter area in the final result, and lower currents (less atomic nuclei) make a dark area in the final result. This technique is similar to scanning electron microscopes, but has the advantage of not requiring a vacuum: there is simply no space between the probe and the surface to fit any air atoms, so no vacuum is necessary. Maintaining a vacuum requires a vacuum pump (which consumes power) and requires the use of expensive materials.
Challenges we ran into
When the angstroms matter and make the difference between a working device and a non-functional device, you will run into challenges.
Acrylic, the material easiest to use at PennApps, has a large thermal expansion coefficient, which is gigantic in the scale of our project: blowing on the sample area impacted the calibration for about ten minutes. This limited the accuracy of the system.
STM’s require some oddball parts. [Walks into the hardware checkout.] “Hey you wouldn’t happen to have a teflon standoff or even just a chunk of teflon.” [And] “Have you got a chunk of steel that weighs maybe... 20, 25 lbs?”
Don’t solder your parts in backwards.
Noise is the enemy! Thermal, vibrational, electromagnetic, your own computer's power :(
What we learned
We learned how to take pictures of atoms, and how to work at the nano scale and smaller.