Editing Molecular nanotechnology (section)

===Existing work on diamond mechanosynthesis===

There is a growing body of peer-reviewed theoretical work on synthesizing diamond by mechanically removing/adding hydrogen atoms <ref>[http://www.MolecularAssembler.com/Papers/TemelsoHAbst.pdf High-level Ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems]. Temelso, Sherrill, Merkle, and Freitas, ''J. Phys. Chem. A'' Vol. 110, pages 11160-11173, 2006.</ref> and depositing carbon atoms <ref>[http://www.rfreitas.com/Nano/JNNDimerTool.pdf Theoretical Analysis of a Carbon-Carbon Dimer Placement Tool for Diamond Mechanosynthesis]. Merkle and Freitas, ''J. Nanosci. Nanotech.'' Vol. 3, pages 319-324, 2003.</ref><ref>[http://www.MolecularAssembler.com/JCTNPengMar04.pdf Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C<sub>2</sub> Mediated Growth of Nanocrystalline Diamond C(110) Surface] {{webarchive|url=https://web.archive.org/web/20090316022613/http://www.molecularassembler.com/JCTNPengMar04.pdf |date=2009-03-16 }}. Peng, Freitas and Merkle. ''J. Comput. Theor. Nanosci.'' Vol. 1, pages 62-70, 2004.</ref><ref>[http://www.MolecularAssembler.com/JCTNMannMar04.pdf Theoretical Analysis of Diamond Mechanosynthesis. Part II. C<sub>2</sub> Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools] {{webarchive|url=https://web.archive.org/web/20090316022605/http://www.molecularassembler.com/JCTNMannMar04.pdf |date=2009-03-16 }}. Mann, Peng, Freitas and Merkle. ''J. Comput. Theor. Nanosci.'' Vol. 1, pages 71-80, 2004.</ref><ref>[http://e-drexler.com/d/05/00/DC10C-mechanosynthesis.pdf Design and Analysis of a Molecular Tool for Carbon Transfer in Mechanosynthesis]. Allis and Drexler. ''J. Comput. Theor. Nanosci.'' Vol. 2, pages 71-80, 2005.</ref><ref>[http://www.MolecularAssembler.com/Papers/JCTNPengFeb06.pdf Theoretical Analysis of Diamond Mechanosynthesis. Part III. Positional C<sub>2</sub> Deposition on Diamond C(110) Surface using Si/Ge/Sn-based Dimer Placement Tools]. Peng, Freitas, Merkle, Von Ehr, Randall and Skidmore. ''J. Comput. Theor. Nanosci.'' Vol. 3, pages 28-41, 2006.</ref><ref>[Horizontal Ge-Substituted Polymantane-Based C<sub>2</sub> Dimer Placement Tooltip Motifs for Diamond Mechanosynthesis]. Freitas, Allis and Merkle. ''J. Comput. Theor. Nanosci.'' Vol. 4, 2007, in press.</ref> (a process known as [[mechanosynthesis]]). This work is slowly permeating the broader nanoscience community and is being critiqued.  For instance, Peng et al. (2006)<ref>{{cite web|url=http://www.MolecularAssembler.com/Papers/JCTNPengFeb06.pdf |title=03CTN01-003 |access-date=2010-09-05}}</ref> (in the continuing research effort by Freitas, Merkle and their collaborators) reports that the most-studied mechanosynthesis tooltip motif (DCB6Ge) successfully places a C<sub>2</sub> carbon [[Dimer (chemistry)|dimer]] on a C(110) [[diamond]] surface at both 300&nbsp;K (room temperature) and 80&nbsp;K ([[liquid nitrogen]] temperature), and that the silicon variant (DCB6Si) also works at 80&nbsp;K but not at 300&nbsp;K. Over 100,000 CPU hours were invested in this latest study.  The DCB6 tooltip motif, initially described by Merkle and Freitas at a Foresight Conference in 2002, was the first complete tooltip ever proposed for diamond mechanosynthesis and remains the only tooltip motif that has been successfully simulated for its intended function on a full 200-atom diamond surface.

The tooltips modeled in this work are intended to be used only in carefully controlled environments (e.&nbsp;g., vacuum). Maximum acceptable limits for tooltip translational and rotational misplacement errors are reported in Peng et al. (2006) -- tooltips must be positioned with great accuracy to avoid bonding the dimer incorrectly. Peng et al. (2006) reports that increasing the handle thickness from 4 support planes of C atoms above the tooltip to 5 planes decreases the resonance frequency of the entire structure from 2.0&nbsp;THz to 1.8&nbsp;THz. More importantly, the vibrational footprints of a DCB6Ge tooltip mounted on a 384-atom handle and of the same tooltip mounted on a similarly constrained but much larger 636-atom "crossbar" handle are virtually identical in the non-crossbar directions. More computed studies modeling still bigger handle structures are welcome, but the ability to precisely position SPM tips to the requisite atomic accuracy has been repeatedly demonstrated experimentally at low temperature,<ref>{{cite web|url=http://www.physics.uci.edu/~wilsonho/stm-iets.html |title=Wilson Ho |publisher=Physics.uci.edu |access-date=2010-09-05}}</ref><ref>{{cite journal|journal=[[Physical Review Letters]]|volume=90|issue=17|page=176102|doi= 10.1103/PhysRevLett.90.176102|bibcode=2003PhRvL..90q6102O|title=Mechanical Vertical Manipulation of Selected Single Atoms by Soft Nanoindentation Using Near Contact Atomic Force Microscopy |pmid=12786084 |last1=Oyabu |first1=N. |last2=Custance |first2=O. |last3=Yi |first3=I. |last4=Sugawara |first4=Y. |last5=Morita |first5=S. |year=2003 |doi-access=free}}</ref> or even at room temperature<ref>{{cite journal |last1=Lapshin |first1=R. V. |year=2004 |title=Feature-oriented scanning methodology for probe microscopy and nanotechnology|journal=Nanotechnology|volume=15|issue=9|pages=1135–1151|issn=0957-4484|doi=10.1088/0957-4484/15/9/006|url=http://www.lapshin.fast-page.org/publications.htm#feature2004|format=PDF|bibcode=2004Nanot..15.1135L}}</ref><ref>{{cite book|author=R. V. Lapshin|year=2011|contribution=Feature-oriented scanning probe microscopy|title=Encyclopedia of Nanoscience and Nanotechnology|editor=H. S. Nalwa|volume=14|pages=105–115|publisher=American Scientific Publishers|location=USA|isbn=978-1-58883-163-7|url=http://www.lapshin.fast-page.org/publications.htm#fospm2011|format=PDF}}</ref> constituting a basic existence proof for this capability.

Further research<ref>{{cite web|url=http://www.MolecularAssembler.com/Nanofactory/AnnBibDMS.htm |title=DMS Bibliography |publisher=Molecularassembler.com |access-date=2010-09-05}}</ref> to consider additional tooltips will require time-consuming [[computational chemistry]] and difficult laboratory work.

A working [[nanofactory]] would require a variety of well-designed tips for different reactions, and detailed analyses of placing atoms on more complicated surfaces. Although this appears a challenging problem given current resources, many tools will be available to help future researchers: [[Moore's law]] predicts further increases in computer power, [[Fabrication (semiconductor)|semiconductor fabrication]] techniques continue to approach the nanoscale, and researchers grow ever more skilled at using [[protein]]s, [[ribosome]]s and [[DNA]] to perform novel chemistry.