Long and medium term goals in molecular nanotechnology Ralph C. Merkle Xerox PARC .

Long and medium term goals in molecular nanotechnology

Ralph C. Merkle

Xerox PARC

www.merkle.com

Fifth Foresight Conference on Molecular Nanotechnology

November 5-8Palo Alto, CA

www.foresight.org/Conferences

The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not anattempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are toobig.

Richard Feynman, 1959

http://nano.xerox.com/nanotech/feynman.html

Molecular nanotechnology(a.k.a. molecular manufacturing)

• 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

Possible arrangements of atoms

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What we can make today(not to scale)

The goal of molecular nanotechnology:

a healthy bite.

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Two ways tocreate new technologies:

• Consider what has been done, and improve on it.

• Design systems de novo based purely on known physical law, then figure out how to make them.

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What we can make today(not to scale)

If the target is “close” to what we can make, the evolutionary method can be quite effective.

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Target

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What we can make today(not to scale)

But there is every reason to believe that molecular manufacturing systems are not “close” to what we can make today.

MolecularManufacturing

To develop tomorrow’s technology starting with today’s

we have to:

• Understand what will be possible tomorrow — which means thinking about things we can not make today

• Understand what is possible today• Find paths from the today we know to the

tomorrow we know is possible.

Working backwards from the goal as well as forwards from the start

• 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

Core molecularmanufacturingcapabilities

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Overview of the development of molecular nanotechnology

If you don't know where you are going, you will probably wind up somewhere else

Laurence J Peter

Two more fundamental ideas

• Self replication (for low cost)

• Programmable positional control (to make molecular parts go where we want them to go)

Von Neumann architecture for a self replicating system

UniversalComputer

UniversalConstructor

Von Neumann's universal constructor about 500,000Internet worm (Robert Morris, Jr., 1988) 500,000Mycoplasma capricolum 1,600,000E. Coli 8,000,000Drexler'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 C program that prints out an exact copy of itself

main(){char q=34, n=10,*a="main() {char q=34,n=10,*a=%c%s%c; printf(a,q,a,q,n);}%c";printf(a,q,a,q,n);}

For more information, see the Recursion Theorem:http://nano.xerox.com/nanotech/selfRep.html

English translation:

Print the following statement twice, the second time in quotes:

“Print the following statement twice, the second time in quotes:”

Drexler’s architecture for an assembler

Molecularcomputer

Molecularconstructor

Positional device Tip chemistry

The broadcast architecture

Macroscopiccomputer

Molecularconstructor

Molecularconstructor

Molecularconstructor

Advantages of the broadcast architecture

• Simpler design

• Fewer parts

• Inherently safe

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

A broadcast method:

•Acoustic transmissions.

10 megahertz is sufficient, faster is feasible

•Pressure actuated ratchets.

125 nm3 volume at 3,200,000 Pascals (~32 atmospheres) provides ~4 x 10-19 joules (~2.5 ev, ~58 kcal/mole).

Simple pressure actuated device

Compressed gas

External gas

Actuator(under tension)

A proposal for a molecular positional device

A proposal for a molecular positional device

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

A simple binding site for butadiyne

A hydrogen abstraction tool

http://nano.xerox.com/nanotech/Habs/Habs.html

Some other molecular tools

Synthesis of diamond today:diamond CVD

• Carbon: methane (ethane, acetylene...)

• Hydrogen: H2

• Add energy, producing CH3, H, etc.

• Growth of a diamond film.

The right chemistry, but little control over the site of

reactions or exactly what is synthesized.

A synthetic strategy for the synthesis of diamondoid structures

• Positional control (6 degrees of freedom)

• Highly reactive compounds (radicals, carbenes, etc)

• Inert environment (vacuum, noble gas) to eliminate side reactions

A modest set of molecular tools should be sufficient to synthesize most stiff hydrocarbons.

http://nano.xerox.com/nanotech/

hydroCarbonMetabolism.html

The theoretical concept of machine duplication is well developed. There are several alternative strategies by which machine self-replication can be carried out in a practical engineering setting.

Advanced Automation for Space MissionsProceedings of the 1980 NASA/ASEE Summer Study

http://nano.xerox.com/nanotech/selfRepNASA.html

We could design and model an assembler today. This would:

• Speed the development of the technology• Allow rapid and low cost exploration of design

alternatives• Provide a clearer target for experimental work• Give us a clear picture of what this

technology will be able to do

Rationale for the design of thesimple assembler

• We want to make diamond• Known reactions for the synthesis of diamond

(diamond CVD) involve reactive species (carbenes, radicals)

• This requires an inert environment and positional control to prevent side reactions

Rationale for the design of a simpler system

• Forget diamond. Use molecular building blocks (there are a lot to choose from)

• Combine building blocks using reactions that are relatively specific. Diels-Alder reactions are a good example

• An inert environment is unnecessary, and positional control can be combined with self-assembly and other methods

Disadvantages of Molecular Building Block (MBB) based systems

• Greatly reduced strength-to-weight ratio• Reduced stiffness (poorer positional control

for a given size)• Slower speed• Much smaller range of things can be

synthesized

Diels-Alder cycloaddition

Steps Towards Molecular Manufacturing, by Markus Krummenacker, Chem. Design Autom. News, 9, (1994). http://www.ai.sri.com/~kr/nano/cda-news/link-chemistry.html

Can we self assemble a robotic arm?

Can we self assemble a Stewart platform?

Can we self assemble an octahedron?

A Stewart platform is an octahedron in which:

• The struts are stiff

• The length of the struts can be changed

• Struts connect at flexible joints

Sliding struts

Needed: a method of controlling the relative position of two struts, i.e., of sliding one strut over a second strut in a controlled fashion to extend and shorten the combined two-strut unit.

Sliding struts

ABCABCABCABCABCABCABCABCABCABCABCABC a a a a | | | | x x x x

XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ

a | x

joins the two struts

Sliding struts

ABCABCABCABCABCABCABCABCABCABCABCABC a c a ca c a |/ |/ | / | xy xy x y x

XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ

a | x join the two struts

c | yand

Sliding strutsABCABCABCABCABCABCABCABCABCABCABCABC c c c c | | | | y y y y

XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ

Joins the two struts, which have nowmoved over one unit.

c | y

Cycling through a-x, c-y and b-z produces controlled relative motion of the two struts.

Can today’s molecular motors be modified so they can be

controllably stepped?

• Chemical signals

• Acoustic signals

• Optical (photochemical) signals

• Other

Core molecularmanufacturingcapabilities

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Overview of the development of molecular nanotechnology

The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, andto do things on an atomic level, is ultimately developed---a development which I think cannot be avoided.

Richard Feynman, 1959

http://nano.xerox.com/nanotech/feynman.html