Important new paper out from Freitas and Merkle



Freitas and Merkle have just published a paper on nine "tooltips" for
mechanosynthesis that possess process closure -- that is, given all
nine, you can build all nine. They were designed with computational
chemistry simulations, rather than being synthesized and then tested,
so there is still a lot of work to do here before one can absolutely
know that the things work, but it is still an amazing achievement.

The paper is over 100 pages long, and required over 105,000 hours of
computer time to do the simulations.

From here, large amounts of work will be needed to validate the
designs with better simulations (i.e. "higher levels of theory" in
computational chemistry parlance) and to actually synthesize the
tooltips and get them attached to scanning microscopy probes.

See: http://www.aspbs.com/ctn/

A Minimal Toolset for Positional Diamond Mechanosynthesis
Freitas, Robert A.; Merkle, Ralph C.
Journal of Computational and Theoretical Nanoscience, Volume
5, Number 5, May 2008 , pp. 760-861(102)
DOI: 10.1166/jctn.2008.002

Abstract:
This paper presents the first theoretical quantitative systems
level study of a complete suite of reaction pathways for
scanning-probe based ultrahigh-vacuum diamond mechanosynthesis
(DMS). A minimal toolset is proposed for positionally controlled
DMS consisting of three primary tools-the (1) Hydrogen Abstraction
(HAbst), (2) Hydrogen Donation (HDon), and (3) Dimer Placement
(DimerP) tools-and six auxiliary tools-the (4) Adamantane radical
(AdamRad) and (5) Germyladamantane radical (GeRad) handles, the (6)
Methylene (Meth), (7) Germylmethylene (GM), and (8) Germylene
(Germ) tools, and (9) the Hydrogen Transfer (HTrans) tool which is
a simple compound of two existing tools (HAbst + GeRad). Our
description of this toolset, the first to exhibit 100% process
closure, explicitly specifies all reaction steps and reaction
pathologies, also for the first time. The toolset employs three
element types (C, Ge, and H) and requires inputs of four feedstock
molecules-CH4 and C2H2 as carbon sources, Ge2H6 as the germanium
source, and H2 as a hydrogen source. The present work shows that
the 9-tooltype toolset can, using only these simple bulk-produced
chemical inputs: (1) fabricate all nine tooltypes, including their
adamantane handle structures and reactive tool intermediates,
starting from a flat passivated diamond surface or an adamantane
seed structure; (2) recharge all nine tooltypes after use; and (3)
build both clean and hydrogenated molecularly-precise unstrained
cubic diamond C(111)/C(110)/C(100) and hexagonal diamond surfaces
of process-unlimited size, including some Ge-substituted variants;
methylated and ethylated surface structures; handled polyyne,
polyacetylene and polyethylene chains of process-unlimited length;
and both flat graphene *** and curved graphene
nanotubes. Reaction pathways and transition geometries involving
1620 tooltip/workpiece structures were analyzed using Density
Functional Theory (DFT) in Gaussian 98 at the B3LYP/6-311+G(2d,p)
// B3LYP/3-21G* level of theory to compile 65 Reaction Sequences
comprised of 328 reaction steps, 354 unique pathological side
reactions and 1321 reported DFT energies. The reactions should
exhibit high reliability at 80 K and moderate reliability at 300
K. This toolset provides clear developmental targets for a
comprehensive near-term DMS implementation program.


Perry

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