intermediate and long term objectives in nanotechnologynanotechnology ralph c. merkle xerox parc
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Intermediate and long term objectives in nanotechnology
Ralph C. Merkle
Xerox PARC
www.merkle.com
Core molecularmanufacturingcapabilities
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Overview of the development of molecular nanotechnology
The abstract goal
• Fabricate most structures that are specified with molecular detail and which are consistent with physical law
• Get essentially every atom in the right place
• Inexpensive manufacturing costs (~10-50 cents/kilogram)
http://nano.xerox.com/nano
Two essential concepts
• Self replication (for low cost)
• Programmable positional control (to make molecular parts go where we want them to go)
Von Neumann's universal constructor about 500,000Internet worm (Robert Morris, Jr., 1988) 500,000Mycoplasma capricolum 1,600,000E. Coli 9,278,442Drexler's assembler 100,000,000Human 6,400,000,000NASA Lunar
Manufacturing Facility over 100,000,000,000
http://nano.xerox.com/nanotech/selfRep.html
Complexity of self replicating systems
(bits)
A proposal for a molecular positional device
One embodiment of the goal:
Drexler’s assembler
Molecularcomputer
Molecularconstructor
Positional device Tip chemistry
Something a bit simpler:the hydrocarbon assembler
• We want to make diamond• The synthesis of diamond using CVD involves
reactive species (carbenes, radicals)• This requires an inert environment and
positional control to prevent side reactions• Focusing our attention on stiff hydrocarbons
greatly simplifies design and modeling
Major subsystems in a simple assembler floating in solution
• Positional device• Molecular tools• Barrier• Trans-barrier transport/binding sites• Neon intake• Pressure actuated ratchets• Pressure equilibration
The value of a goal:we can work backwards from it
(or: it’s hard to build something if you don’t know what it looks like)
• Backward chaining (Eric Drexler)• Horizon mission methodology (John
Anderson)• Retrosynthetic analysis (Elias J. Corey)• Shortest path and other search algorithms in
computer science• “Meet in the middle” attacks in cryptography
The focus today: self replication and molecular tools
• Molecular tools are made from feedstock molecule(s)
• Molecular tools are made using an existing set of molecular tools
• Starting with one set of molecular tools, we must end up with two full sets of molecular tools
http://nano.xerox.com/nanotech/hydroCarbonMetabolism.html
A hydrogen abstraction tool
http://nano.xerox.com/nanotech/Habs/Habs.html
Some other molecular tools
Thermal noise,a classical equation:
2 = kT/ks
• is the mean positional error (~0.02 nm)• k is Boltzmann’s constant (~1.38 x 10-23 J/K)• T is the temperature (~300 K)
• ks is the stiffness (~ 10 N/m)
• See page 91 of Nanosystems for a derivation and further discussion
Feedstock
• Acetone (solvent)• Butadiyne (C4H2, diacetylene; source of
carbon and hydrogen)• Neon (inert, provides internal pressure)• “Vitamin” (transition metal catalyst such
as platinum; silicon; tin)
http://nano.xerox.com/nanotech/hydroCarbonMetabolism.html
These molecular tools should be able to
synthesize a remarkably wide range of stiff
hydrocarbons.
http://nano.xerox.com/nanotech/
hydroCarbonMetabolism.html
Overview
• Start with molecular tools and butadiyne
• Finish with two sets of molecular tools
• Assumes the availability of positional control in an inert environment (e.g., vacuum)
Positioning and initially bonding to a molecule
• Intermolecular forces must be used• Access is required for the molecular tool(s)
which will first bond to the molecule• Once attached covalently to a molecular tool,
further positional control can be achieved by moving the molecular tool
• To position butadiyne for its first bonds, think of a hot dog in a hot dog bun
The first bonds to butadiyne
• Radicals could in principle attach at any of the six atoms in butadiyne
• Carbenes could in principle insert into any of the five bonds in butadiyne
Creating twohydrogen abstraction tools
Refreshing ahydrogen abstraction tool
Separating two hydrogen abstraction tools that are bonded
together
Radicals weaker than the hydrogen abstraction tool can be
created by abstracting a hydrogen from the appropriate
precursor
We can dispose of excess hydrogen by making hydrogen
rich structures
Extending ahydrogen abstraction tool
Transferring a dimer from a polyyne to a cumulene
(the kind of reaction needed to refresh the carbene tool)
Parts closure
• We must be able to synthesize all tools from the available feedstock and a pre-existing set of molecular tools
• Quantitative parts closure requires that such synthesis does not cause a depletion of the pre-existing set of tools
• See http://nano.xerox.com/nanotech/ hydroCarbonMetabolism.html for further discussion
Core molecularmanufacturingcapabilities
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Overview of the development of molecular nanotechnology
The design and modeling of a simple assembler could be done
with existing capabilities.This would:
• Clarify the goal• Speed the development of the technology• Allow rapid and low cost exploration of design
alternatives• Clarify what this technology will be able to do