Mechanosynthesis
Mechanosynthesis
In conventional chemical synthesis or chemosynthesis, reactive molecules encounter one another through random thermal motion in a liquid or vapor. In a hypothesized process of mechanosynthesis, reactive molecules would be attached to molecular mechanical systems, and their encounters would result from mechanical motions bringing them together in planned sequences, positions, and orientations. It is envisioned that mechanosynthesis would avoid unwanted reactions by keeping potential reactants apart, and would strongly favor desired reactions by holding reactants together in optimal orientations for many molecular vibration cycles. Mechanosynthetic systems would be designed to resemble some biological mechanisms.
While the description of mechanosynthesis given above has not yet been achieved, primitve mechanochemistry has been performed at cryogenic temperatures using scanning tunneling scraping electron microscopes). So far, such devices provide the closest approach to fabrication tools for molecular engineering.
Broader exploitation of mechanosynthesis awaits more advanced technology for constructing molecular machine systems - including a molecular assembler or precursors thereof.
It has been suggested, notably by K. Eric Drexler, that mechanosynthesis will be fundamental to molecular manufacturing based on nanofactories capable of building macroscopic objects with atomic precision. The potential for these has been disputed, notably by Nobel Laurate Richard Smalley, leading to a famous dispute between the two of them - see nanotechnology.
In part to resolve this and related questions about the dangers of industrial accidents and runaway events equivalent to Chernobyl and Bhopal, and the more remote issue of ecophagy, grey goo and green goo (various potential disasters arising from runaway replicators, which could be built using mechanosynthesis) the UK Royal Society and UK Royal Academy of Engineering in 2003 commissioned a study to deal with these issues and larger social and ecological implications, led by mechanical engineering professor Ann Dowling. This was anticipated by some to take a strong position on these problems and potentials - and suggest any development path to a general theory of so-called mechanosynthesis.
However, the Royal Society’s nanotech report did not address molecular manufacturing at all, except to dismiss it along with gray goo.
Existing Work on Diamond Mechanosynthesis
There is some peer-reviewed research on synthesizing diamond by mechanically depositing carbon atoms (a process known as mechanosynthesis).
- Theoretical Analysis of a Carbon-Carbon Dimer Placement Tool for Diamond Mechanosynthesis. Merkle and Freitas, J. Nanosci. Nanotech. 2003, Vol. 3, No. 03.
- Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated Growth of Nanocrystalline Diamond C(110) Surface. Peng, Freitas and Merkle. J. Comput. Theor. Nanosci. Vol. 1, No. 1 2004.
- Theoretical Analysis of Diamond Mechanosynthesis. Part II. C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools. Mann, Peng, Freitas and Merkle. J. Comput. Theor. Nanosci. Vol. 1, No. 1 2004.
For the paper by Mann, et al., the researchers used over 5 years of CPU time to simulate a series of “tool tips” which could be used to place a pair of carbon atoms (a dimer) onto a diamond surface. The most promising tip succeeded in placing the carbon dimer onto the diamond surface once in five simulations, and it had to be positioned with great accuracy to avoid bonding the dimer incorrectly. Furthermore, the tips were difficult to recharge with a second carbon dimer, and were only stable in carefully controlled environments.
Further research to consider alternate tips will require time-consuming computational chemistry and difficult laboratory work.
See also: chemosynthesis
External links
- Bibliography by Robert Freitas