Intermediate and long term objectives in nanotechnology

1. Intermediate and long term objectives in nanotechnology Ralph C. Merkle Xerox PARC www.merkle.com

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3. 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

4. Two essential concepts • Self replication (for low cost) • Programmable positional control (to make molecular parts go where we want them to go)

5. Complexity of self replicating systems (bits) • Von Neumann's universal constructor about 500,000 • Internet worm (Robert Morris, Jr., 1988) 500,000 • Mycoplasma capricolum 1,600,000 • E. Coli 9,278,442 • Drexler's assembler 100,000,000 • Human 6,400,000,000 • NASA Lunar • Manufacturing Facility over 100,000,000,000 http://nano.xerox.com/nanotech/selfRep.html

6. A proposal for a molecular positional device

7. One embodiment of the goal: Drexler’s assembler Molecular computer Molecular constructor Positional device Tip chemistry

8. 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

9. 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

10. 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

11. 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

12. A hydrogen abstraction tool http://nano.xerox.com/nanotech/Habs/Habs.html

13. Some other molecular tools

14. Thermal noise,a classical equation:s2 = kT/ks • s 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

15. 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

16. A simple binding site for butadiyne

17. These molecular tools should be able to synthesize a remarkably wide range of stiff hydrocarbons. http://nano.xerox.com/nanotech/ hydroCarbonMetabolism.html

18. 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)

19. 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

20. 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

22. Creating twohydrogen abstraction tools

24. Refreshing ahydrogen abstraction tool

26. Separating two hydrogen abstraction tools that are bonded together

28. Radicals weaker than the hydrogen abstraction tool can be created by abstracting a hydrogen from the appropriate precursor

29. We can dispose of excess hydrogen by making hydrogen rich structures

30. Extending ahydrogen abstraction tool

32. Transferring a dimer from a polyyne to a cumulene(the kind of reaction needed to refresh the carbene tool)

34. 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

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36. 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