Check out this news item:
Researchers at the Aono Atomcraft Project in Japan, using an STM, are now able to extract a single silicon atom from the surface of a silicon crystal and rebond it to the surface at a different location. Atoms translocated in this manner can be re-removed without disarranging the underlying atomic layers. Atoms brought from afar can be used to repair holes in the silicon surface, or they can be used to build structures on top of the surface. [J. Vac. Sci. Technol. B 12(4): 2429-2433, Jul/Aug94] Folks, this looks an awful lot like real nanotechnology.
Pretty exciting stuff!
But if you look closely at the citation, you'll see that it happened a decade ago. So what happened since? Why didn't this lead straight to "real nanotechnology"?
The tool they were using, the STM (scanning tunneling microscope), has a limitation: it can only detect objects that it can send electrons through. And pure silicon crystal is an insulator. Add a few impurities, and it conducts; so they presumably were working on the surface of a "doped" crystal, and were able to make 2D patterns. But I guess they couldn't figure out how to make small conductive 3D silicon structures. Or, maybe, the project's funding ran out before they were able to: it was only funded through 1994.
Any lessons for today? Yes, though they're tentative. One lesson is that a single technique, no matter how impressive, probably won't be enough to get us to the ultimate goal: digitally-controlled nano-building-nano.
Another lesson is that a decade ago, people were already able to do covalent single-atom chemistry with atomic precision. They even had the process automated; their web site shows patterns consisting of many (dozens? hundreds?) displaced atoms. Take a simple system--the surface of a silicon crystal--and you can make intricate patterns with atomic precision by doing simple things to it repeatedly. I found that blurb in a google search, and reading it out of context, I first assumed that it must have been done within the last year. But no, they did it with decade-old computers, tools, and theory.
Now let's go back to that tool limitation. An STM probably can't build 3D silicon shapes. But there's a related tool called an AFM (atomic force microscope) that measures force rather than conductivity. It can "see" silicon just fine. And last year, a silicon atom was removed from a surface and then replaced using an AFM.
Can nanomachine-building nanomachines be made out of silicon? It seems pretty likely. Micron-scale AFMs have already been built using MEMS processes. So does this represent a path to molecular manufacturing, and if so, how close are they? We can't know, because no one in the U.S. has bothered to develop the theory of "stiff nanomachines" in enough detail to compare the possibilities with the experiments.