interesting! the axidraw v3 that I used for this (https://shop.evilmadscientist.com/productsmenu/846) has a 0.0125mm stepper resolution, which means that it is pretty close to not-worth-it to go any finer since the sizes of the scratches are already many microns wide. But certainly with better etching technology that would be a super cool update!
Alexander's results show a movement range of 1.25um, 10 times smaller than the 12.5um step of your system, so in its current form it wouldn't be suitable for interpolating motor steps.
Also potentially interesting is Alexander's "cut-and-pull" technique for making scanning tips with a single atom at the point. I can't find the original reference, but here's a description:
The single atom would likely immediately wear down if used for scribing, but even if it wore down to multiple atoms wide it might still produce a very narrow line? I wonder what the effects of using an STM on a photosensitive plate would be, whether the strong electric field at the tip would lead to very narrow photographic lines?
