In press, available in the Journal of Computational and Theoretical Nanoscience (expected early 2007). Part of continuing work presented in far greater detail at the molecular assembler site. One of the many aspects of molecular nanotechnology this work begins to address is the cost/benefit of different tooltip motifs in the mechanosynthesis of atomically-precise structures. Just as the same class of chemical reaction will require different reaction conditions for different classes of substrates, no single tooltip can be expected to enable the manufacture of any arbitrary structure. Much of the work to date in this area has been on carbon dimers (C2), but the same principles addressed in this article will apply to other schemes being examined (as well as in-progress protocol development for nanoEngineer-1).
R. A. Freitas Jr., D. G. Allis and R. C. Merkle
Abstract: After a systematic search for representative Ge-substituted polymantane-based carbon dimer (C2) placement tool motifs for positionally-controlled vacuum diamond mechanosynthesis (DMS) using semi-empirical (AM1) and classical molecular dynamics methods, 24 potentially useful tooltip structures were examined theoretically using Density Functional Theory to assess dimer transfer energetics, identify accessible pathological structures, and evaluate all tooltip candidates using practical engineering design criteria including tool aspect ratio, vibrational stability, and protection from hydrogen poisoning. Members of this family of 24 tooltips should be stable in vacuum and should be able to hold and position a C2 dimer in a manner suitable for positionally-controlled dimer placement DMS reactions at room temperature.
Keywords: Adamantane, Carbon, Diamond, Dimer Placement, DMS, Germanium, Mechanosynthesis, Nanotechnology, Positional Control, Tooltips