https://phys.org/news/2019-05-atoms-electron.html
Electron microscope researchers have been getting close to single atom assembly for awhile. They were pretty close last year - getting down to two nanometer or so(which can fit multiple atoms).
I don't think this electron microscope nano-manbufacturing is exactly what say Eric Drexler would envision. The electron microscope guys, by their own admission, describe this as atom soccer ball, using relativistic electron beams. But, they have worked out the math and put it into an A.I. algorithm to boot! I mean, they've created an A.I. program that calculated how much energy to hit a particular atom, what the movement of the atom will be; but, it's still probabilistic.
As they note, the electron beam is faster than a Scanning Tunneling microscope(which I don't feel like describing right now), and can work parallel electron beams.
The rate of advancement, of bringing in parallel bemas, and maybe improving the probabilities should prove interesting.
They say this can only assemble a thousand atoms. Assembling a thousand atoms would be an accomplishment for now. But, if they can assemble a thousand atoms structure in a microsecond, then, they should be able to, either add another thousand atoms to the structure, or create another thousand atom structure in the next micro-second. Once again, the rate of advancement should prove interesting.
