Mechanochemistry at the Single Bond Limit: Towards "Deterministic Epitaxy" [Resubmission]

Can we manipulate atoms just like we control bits of information in a computer? Could we ever build a matter compiler - a device that positions atoms, one by one, to construct a macroscopic product like a table, a computer, or even a building? In other words, could we ultimately push 3D printing all the way down to the atomic level?

This is the essence of the highly controversial "molecular manufacturing" concept put forward by Eric Drexler in the eighties, originally inspired by Richard Feynman's thoughts on the ultimate limits of miniaturisation back in the late fifties. Drexler's ideas were, and continue to be, widely critiqued and criticised by many (including the authors of this proposal) but at the core of his molecular manufacturing scheme is a demonstrably valid process: computer-controlled and atomically precise chemistry driven purely by mechanical force. This type of mechanochemistry is now implemented in the lab (and studied theoretically) by a small number of research groups across the world, including those involved in this proposal.

Our core objective is a little less grandiose than the fabrication of a macroscopic or, indeed, microscopic object using single atom manipulation. Nonetheless, it is an exceptionally challenging goal: the fabrication of a 3D object -- a nanoparticle -- an atom at a time. Although there are now many impressive examples of single atom control being used to form a variety of artificial structures at surfaces -- with IBM's recent "A Boy And His Atom" video, which has now amassed over 5M views, being a particularly elegant demonstration -- to date a 3D object has not been constructed. There are very good reasons for this; extending atomic manipulation and positioning to the third spatial dimension will involve a very different approach to interacting with atoms and molecules. Developing those protocols forms the core of our proposal.

It was the invention and subsequent application of a radically different type of microscope called the atomic force microscope (AFM) which enabled computer-controlled single atom mechanochemistry (of the type envisaged by Drexler) to be realised. The AFM is a microscope like no other -- it doesn't use lenses, mirrors, or any type of optical element to generate an image. Instead, an atomically sharp tip is brought close (within a few atomic diameters) to a surface. At this distance a number of important forces and interactions kick in, including, at the smallest separations, the formation of a chemical bond between the atom at the end of the tip and an atom directly underneath the probe. By scanning the tip back and forth across the surface whilst monitoring how the chemical force changes it's possible to build up an image of a surface with not only atomic, but single bond, resolution.

AFM is capable of a lot more than 'just' ultrahigh resolution imaging, however. The tip-sample force field can be mapped, the strength of single bonds measured, and, of key importance to this proposal, single atoms can be manipulated via chemomechanical force alone. Unlike its predecessor, the scanning tunnelling microscope, the AFM -- particularly the variant we use in our research, dynamic force microscopy (DFM) -- does not rely on the flow of an electrical current between tip and sample. With DFM, atoms can be moved through chemical force alone and this, along with the much higher sensitivity of DFM to the orientation and strength of single chemical bonds, has the potential to provide the exceptionally high levels of atomic-level control required to fabricate 3D nanostructures.

As discussed in the introduction to our Pathways to Impact statement, the research we propose is unashamedly fundamental science. We did not develop the research programme with a "user base" or a commercial application in mind, and it would be disingenuous to suggest otherwise. Our pathways to impact are thus entirely focused on public engagement -- an aspect of academic research to which the investigators are entirely committed, and in which the PI has invested considerable effort over recent years (see, for example, the "Beyond The Ivory Tower" tab at http://www.nottingham.ac.uk/physics/people/philip.moriarty).

There are five primary aspects of the impact stemming from our research (in addition to the academic beneficiaries listed in the preceding section). We summarise these aspects below. More detail is given in the Pathways to Impact statement.

1. Social Media. (i) Sixty Symbols. The School of Physics and Astronomy at the University of Nottingham has a long-standing collaboration with Brady Haran, a talented and prolific video journalist, on the Sixty Symbols YouTube project. Sixty Symbols is a series of short videos which present various aspects of physics to a wide audience (the subscriber base is currently a little over 435,000, with a total of 36 million views across all of the videos). A recent article in Physics World, written by the PI, describes the motivation and aspirations for the Sixty Symbols project: http://www.nottingham.ac.uk/~ppzstm/pdfs/Moriarty_youtube.pdf.

Videos related to previous (EPSRC-funded) dynamic force microscopy research in the Nottingham group have attracted a total of over 250,000 views and led to very many comments being exchanged under the videos, and via e-mail. The Sixty Symbols audience is worldwide and spans a very wide range of ages, backgrounds, and educational experience, from primary school children to emeritus professors. We have requested modest funding (£1K) to film a Sixty Symbols video based on the "3D printing with atoms" premise underpinning our research.

(ii) Blogging and Twitter. Both Nerlich and Moriarty blog regularly. They will post regular updates on both the research and the wider context of the "scientific method in action", throughout the project.

2. The Rock-Science interface. As discussed in the Physics World article cited above, there is a reasonably strong overlap in a Venn diagram of fans of rock music and physicists. However, more importantly -- and as we have found for a previous mathematics-inspired (and mathematics-derived) song [see http://periodicvideos.blogspot.co.uk/2012/07/metallizing-phi-by-phil-moriarty.html ] -- music can be used to connect with an audience that may not previously have had any interest in (nano)science. We have therefore requested funding to support the development/recording (including a Sixty Symbols video) of a rock song based on the implications of the atom-technology research we have proposed.

3. MekNano. We propose to develop a video game based on the mechanochemistry underpinning our proposed research. The PI has already "pitched" this idea to the final year project organisers in the School of Physics and Astronomy at Nottingham, and it has been approved. Our aim is to ensure that the gameplay is realistic and based on an accurate representation of, for example, the orientation of electron orbitals during the simulated assembly process. As with Impact #1 and #2 above, our aim is to connect with an audience that may not necessarily have had a prior interest in scientific research.

4. Graphic novel. The PI has recently established a collaboration with the script-writer Shey Hargreaves to develop a graphic novel based on atom manipulation research.

5. Reporting Research in Real Time. Nerlich will spend two hours per week within the Nottingham Nanoscience group, to observe and report (via social media -- see #1 above) on how scientific research proceeds in a state-of-the-art project.