From a purely scientific angle, so presumably less amenable to mass production, why doesn't anyone use FT-ICR mass spectrometers to assemble say a unit cell?
There is a good classic primer on FT-ICR, mostly focused on analysis (mass spectrometry) but also mentioning activation energies for reactions and measurement of kinetics etc.
https://warwick.ac.uk/fac/sci/chemistry/research/oconnor/oco...
If you dunk a bunch of chemicals (for simplicity think wet chemistry) in a vial, all reactions and side reactions are simultaneously occuring, so one has little control over what happens on an atomic scale.
FT-ICR can be used to observe the state AND to manipulate the state. Its like having a compact particle collider, but instead of the high (TeV) energy in CERN etc. its just chemical energy levels.
It happens in high vacuum, so low densities of species, hence not amenable to mass production.
But the instrument is both eyes and hands: one can identify the frequencies corresponding to each ionized molecule, and selectively energize or de-energize specific species to encourage or prevent main and competing reactions, by pumping or damping specific frequencies.
One may build up a molecule in elementary steps and eject finished molecules. Those steps can occur at the same time in the same vessel. Its like having a miniature digitally controlled chemical plant, without having to redo all the pipework if you decide to use a different pathway here or there.