you have watched those videos of sodium acetate crystallization where an arcing form spreads through a fluid now visualize a fluid that supports two or three different crystal shapes simultaneously
you could get the crystals to form with light beams or holograms building up an image like a 3d printer
yet there is a better way
photon teleportation
you can photoncast a 3d pattern of photons nto the fluid to create a wide variety of precisely spaced crystal seed points that grow at predictable rates you could use different frequencies of light to create different shapes that grew at different rates to make structures
The link is to a quantum linked photon camera where "If the first photon stops at one point on the object plane, the second photon can only be observed at the corresponding point on the image plane," thus 3d photoncasting of seed crystals is a way to build nanostructures
its a big nanoassembler