A Minimal Toolset for Positional Diamond Mechanosynthesis

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 sheet 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.