Yesterday, we announced that CRN has prepared a list of thirty essential studies that must be performed before we can have an adequate understanding of the potential societal impacts of nanotechnology.
Here is a look at part of recommended study #1: "Is mechanically guided chemistry a viable basis for a manufacturing technology?"
Molecular manufacturing is based on the idea of using physical manipulation to cause reliable chemical reactions, building components for products (including manufacturing systems) from precise molecular fragments. Although several flavors of this have been demonstrated (including the ribosome), there is still skepticism in some circles as to whether a self-contained manufacturing technology can be based on this.
Subquestion A: Is there anything wrong with the basic theory of using programmably controlled nanoscale actuators and mechanics to do chemistry?
Preliminary answer: To the best of our knowledge, there is nothing wrong with the theory, and it has been demonstrated in certain cases: semi-programmable nanoscale ribosomes do positional chemistry. Nanoscale actuators and mechanical devices exist in a variety of forms and designs. Sub-angstrom-scale precision adequate to do reliable chemistry may be achieved by any of several mechanisms. The question is what families of chemistry are possible. Quite a few have been proposed.
Subquestion B: Can diamond robotics do scanning-probe vacuum chemistry to build diamond with low error rates? Even at room temperature?
Preliminary answer: Scanning probe microscopes have already done several kinds of covalent chemistry, with and without electric currents. Basic theory says that a stiff low-energy covalent surface should not reconstruct or deform easily, even if one or two reactive atoms are brought near it; those atoms can then be applied to a chosen spot on the surface and perform a predictable reaction.
It has not been difficult to find deposition reactions that, in simulation, can be used to build diamond. These reactions or similar ones will probably work in practice.
According to Drexler's analysis in Nanosystems, achieving the necessary precision for diamond synthesis at room temperature appears to require an overall stiffness between workpiece and probe of 10 N/m. This assumes that the required precision is on the order of a bond length, 1.5 Angstrom. Diamond nanoscale components can probably satisfy this requirement for room-temperature diamond mechanosynthesis.
Freitas and Merkle have studied a dimer deposition reaction on the (110) diamond face. They found that for this particular tool tip and reaction, positional accuracy of 0.1 angstrom was required to distinguish between configurations. If this is the case in general, it may affect the temperature at which the synthesis can be carried out reliably. Note, however, that low temperatures are good because they improve the efficiency of computation.
Subquestion C: Will there be substantial difficulty in automating and scaling up fabrication chemistry or subsequent assembly of parts?
Preliminary answer: This depends on many factors: whether the actuation method can easily be controlled in parallel, whether the chemistry is reliable enough to proceed without error checking, whether the parts will be easy to grip and manipulate, whether the parts will stick easily when assembled correctly (and not before), and for scale-up, whether control and actuation can be implemented in suitable nanoscale technology. Architecture-level designs and calculations have been done for diamondoid mechanosynthesis systems, and they appear to scale quite well to tabletop systems making integrated decimeter-scale products and fabricating their own mass in a few hours.
Provisional conclusion: Any of several types of mechanically guided chemistry appear to be viable technologies for inexpensive, high-volume molecular manufacturing of complex, high-performance products.
CRN's initial basic findings (preliminary answers and provisional conclusions) for all thirty studies should be verified as rapidly as possible. Because our understanding points to a crisis, a parallel process of conducting the studies is strongly preferred.
We are actively looking for researchers interested in performing or assisting with this work. Please contact CRN Research Director Chris Phoenix if you would like more information or if you have comments on the proposed studies.