DIY scanning tunnelling microscope Answered
Sacha De'Angeli has announced the release of "version 0.1" (proof of concept) for a do-it-yourself scanning tunnelling microscope. If you already know what an STM is, my work here is done.
For the rest of you, a scanning tunnelling microscope moves a very fine ("single atom sharp") tip across a surface.Electrons can jump between the surface and tip, leading to a varying electric current which can be amplified and measured. How well the electrons can jump depends exponentially on the width of the gap. Near an atom is closer than between atoms, so by moving the tip in very small (nanometer) increments, you can image the atomic structure of the surface. With a less sharp tip, or coarser position control, you can still image surface structure, steps, defects, etc.