Intermediate and long term objectives in nanotechnologynanotechnology Ralph C. Merkle Xerox PARC

Core molecular manufacturing capabilities Today Products 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)

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

Von Neumann's universal constructorabout 500,000 Internet worm (Robert Morris, Jr., 1988)500,000 Mycoplasma capricolum1,600,000 E. Coli9,278,442 Drexler's assembler100,000,000 Human6,400,000,000 NASA Lunar Manufacturing Facilityover 100,000,000,000 Complexity of self replicating systems (bits)

A proposal for a molecular positional devicemolecular positional device

One embodiment of the goal: Drexler’s assembler Molecular computer Molecular constructor Positional deviceTip 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 solutionsimple assembler 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 hydroCarbonMetabolism.html

A hydrogen abstraction tool

Some other molecular tools

Thermal noise, a classical equation:  2 = kT/k s  is the mean positional error (~0.02 nm) k is Boltzmann’s constant (~1.38 x J/K) T is the temperature (~300 K) k s is the stiffness (~ 10 N/m) See page 91 of Nanosystems for a derivation and further discussionNanosystems

Feedstock Acetone (solvent) Butadiyne (C 4 H 2, diacetylene; source of carbon and hydrogen) Neon (inert, provides internal pressure) “Vitamin” (transition metal catalyst such as platinum; silicon; tin)

A simple binding site for butadiynebinding site

These molecular tools should be able to synthesize a remarkably wide range of stiff hydrocarbons. 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 two hydrogen abstraction tools

Refreshing a hydrogen 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 a hydrogen 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 hydroCarbonMetabolism.html for further discussionhttp://nano.xerox.com/nanotech/ hydroCarbonMetabolism.html

Core molecular manufacturing capabilities Today Products 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