AFM Atom Manipulation: A surprising technique

by Eric Drexler on 2009/03/14

AFM images of steps in constructing a precise atomic pattern.
Replacing tin atoms
with silicon
using an AFM

“Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy”
Y Sugimoto, et al., Science, 322: 413–417 (2008).

Shortly before I launched Metamodern, Science published a remarkable paper by Sugimoto et al. describing atom-by-atom manipulation of a monatomic layer of tin (Sn) on silicon (Si). The animation to the right shows the steps in constructing a pattern of Si atoms that spells ‘Si’. Each frame is an atomic force microscope image made with the same tip used to construct the pattern, part of a commercially available silicon cantilever.

The process works by interchanging atoms between the tip and the surface. Some tips deposit Si, others deposit Sn, some alternate. Once a suitable tip is found, the process is reproducible. The authors have simulated the process using density functional methods and computing resources from the Barcelona Supercomputing Center, home of the beautiful MareNostrum machine (I couldn’t resist the temptation to include a picture).

The MareNostrum supercomputer in Barcelona.

The ‘Si’ structure took 1.5 hours to make. Most of this time was spent imaging, and some of this time was spent waiting for a new Si atom to appear on the tip. I say “appear”, because the tips recharge spontaneously, from material already on the tip, not by picking up atoms from the surface.

A fabrication process like this is far from being high-throughput manufacturing, and my bets are on self-assembly as a path forward, but the research illustrates several points:

  • Mechanosynthesis isn’t restricted to processes like those found in ribosomes and nonribosomal peptide synthases: Physics allows mechanosynthetic processes quite different from those based on positional control of conventional reactive monomers.
  • Fabrication processes are are often discovered, not designed. I doubt that the researchers expected to see this behavior, and the spontaneous recharging of tips is (to me) very surprising.
  • For a wide range of applications, quantum chemistry works. Simulations showed how atom interchange can work, and simulations of the same kind could be used to discover and design other processes — which could seldom be implemented without a way to make atomically precise tips that meet the design specification.
  • Techniques for atomically precise fabrication are accumulating. The first contributions came from chemical synthesis, more came from biotechnology, and yet others from materials science. Direct physical manipulation methods are becoming part of the toolkit.

Techniques for direct physical manipulation have thus far remained a laboratory curiosity, but they may gain practical value, and even now they illustrate direct positional control of the sort that will be characteristic of advanced mechanosynthetic methods.

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{ 9 comments… read them below or add one }

Scott Jensen March 14, 2009 at 11:44 pm UTC

Could the process in that video clip be used to help create a computer chip atom by atom? Has anyone done something like that? I’m not meaning it be a process to be used by the computer industry but simply to show that such a chip could be made atom-by-atom and operate. To me, it wouldn’t matter if it operated at a relatively slow speed. Just sort of a proof of concept kind of thing.

ValkYrie Ice March 16, 2009 at 11:48 pm UTC

My question is what is the feasibility of setting up this kind of manipulation in parallel? Would it be possible to create a single AFM that has multiple tips that carry out the exact same process over the scale of several nanometers? I’ve read recently that someone had discovered a process which used a particular insulator that when the atoms were aligned on the surface, became conductive, and could be used to make a variety of nanoscale components such as transistors, memristors, and the majority of components need to create computer processors. Could a method like this be scaled to produce modular components that could then be linked into a working computer?

Tom Craver March 17, 2009 at 12:01 am UTC

If a method like this could be combined with Single Layer Deposition , it seems like it’d be getting awfully close to allowing building 3D structures – embedded in a solid, so the next step would be figuring out how to “free” the structure.

Esteban March 17, 2009 at 8:11 am UTC

I hope the replacement of Mare Nostrum( It will ¨Mare Incognito¨
with 10 Petaflops for next year) accelerate the manufacture of
atomic chip.

Eric Drexler March 22, 2009 at 8:22 pm UTC

@ Scott Jensen, ValkYrie Ice –

Atomically precise manipulation has been demonstrated in several tip/surface systems, but to date none have been of practical use. Most work with materials of the wrong kind, all of them are very slow, and parallel systems with many tips — in the range that can be considered today — would still be very slow.

There has been some work with potentially useful materials, however, and devices of some kinds would have practical uses even at a high cost per unit (and therefore an astronomical cost per system of chip-scale complexity). Here, I have in mind sensors that produce unique or high-value information. Really fast gene-readers might qualify, for example.

Looking forward, productive nanosystems will eventually enable atomically precise manufacturing with enormous parallelism, making the limitations I mentioned above obsolete. There’s an intermediate technology base to build first, however, so this isn’t a challenge that can be approached directly. Instead, the promise of these systems provides a motive to work on pathway-relevant technologies. A theme of my writing on this blog has been those technologies — what they are, and what’s needed to make progress.

Eric Drexler March 22, 2009 at 8:26 pm UTC

@ ValkYrie Ice

Re. insulating materials with conductive interfaces and other surprising properties, I find these systems very interesting and have been meaning to write about them. Part of what holds me back is that there’s so much to say.

To date, atomically precise control has been in one dimension, through atomic layer deposition. Adding lateral control on a layer-by-layer basis should lead to further surprising results, but would require a qualitatively different kind of fabrication technology.

Scott Jensen March 29, 2009 at 3:54 pm UTC

I understand it would be very slow but if it could be used to create even the simplest computer chip, that would be a proof of concept. Much like how IBM spelled out its name using atoms. If someone were to make the first nano-scale computer chip, it would get press and possibly spark off a competition. Possibly a number of competition. The most powerful nan0-scale computer chip … shortest time to make X computer chip … and so forth. It might get scientists to go, “Hey, if we did it this way, it would speed up the process ten fold.” and so forth which might be the way innovations could help bring about the Nano Age. What do you think, Eric?

Eric Drexler April 1, 2009 at 4:20 am UTC

Yes, proof-0f-concept demonstrations can be valuable even when they’re very far from being practical. For new digital logic devices, a major milestone is the ability to make a smaller or higher-frequency circuit (ring oscillators are common), and this is enough to prove quite a lot.

I was tempted to say that commercial motivations would make a prize almost irrelevant, but this might not be true. With a tip-directed fabrication technology, commercially practical microprocessor applications might remain remote even after it became possible to make devices on a highly non-commercial basis. If so, then a well-structured prize might be very effective.

Scott Jensen April 1, 2009 at 5:52 pm UTC

A prize is a great idea. How about you do a blog post on it? I could see a lot of college students gunning for the prize … if their university has the nanotech equipment so they can do so.

Also, this blog post is about to go into the archive so its readership will dramatically drop off then. :-P

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