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Systems Issues in the Development of Nanotechnology

Ralph C. Merkle, Ph.D.

Principal Fellow, Zyvex

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• Fabricate most structures consistent with physical law

• Get essentially every atom in the right place• Inexpensive (~10-50 cents/kilogram)

The Vision

The goal

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• Self replication (for low cost)• Positional assembly (so parts go where we

want them to go)• Both concepts are applicable at many

different sizes

The Vision

Two important ideas

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• Von Neumann architecture• Bacterial self replication• Drexler’s original proposal for an assembler• Simplified HydroCarbon (HC) assembler• Exponential assembly• And many more…

There are many ways to make a replicating system

Replication

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The Von Neumann architecture

UniversalComputer

UniversalConstructor

http://www.zyvex.com/nanotech/vonNeumann.html

Self replication

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Elements in Von Neumann Architecture

• On-board instructions• Manufacturing element• Environment

• Follow the instructions to make a new manufacturing element

• Copy the instructions

Self replication

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The Von Neumann architecture

http://www.zyvex.com/nanotech/vonNeumann.html

Self replication

Manufacturingelement

Newmanufacturingelement

Instructions

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The Von Neumann architecture

http://www.zyvex.com/nanotech/vonNeumann.html

Self replication

Instructions(tape)

Read head

Manufacturingelement

Newmanufacturingelement

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Replicating bacterium

Self replication

DNA

DNA Polymerase

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Elements in replicating bacterium

• Instructions (DNA polymer)• Ribosome interprets mRNA derived from DNA

(basic positional assembly)• Proteins self assemble• Liquid environment with feedstock molecules• Able to synthesize most proteins that aren’t too

long

Self replication

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http://www.foresight.org/UTF/Unbound_LBW/chapt_6.html

Self replicationDrexler’s proposal for an assembler

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Elements in Drexler’s assembler

• Instructions (polymer)• Molecular computer• Molecular positional device (robotic arm)• Liquid environment with feedstock molecules• Able to synthesize most arrangements of

atoms consistent with physical law

Self replication

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http://www.zyvex.com/nanotech/selfRep.html

Broadcast replication

Macroscopiccomputer

Molecularconstructor

Molecularconstructor

Molecularconstructor

Broadcast architecure

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Advantages of broadcast architecture

• Smaller and simpler: no instruction storage, simplified instruction decode

• Easily redirected to manufacture valuable products

• Inherently safe

Broadcast replication

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Compressed neon

Approximate dimensions:1,000 nm length100 nm radius

Broadcast replication

Overview of HC assembler

http://www.zyvex.com/nanotech/casing.html

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Elements in HC assembler

• No on-board instructions (acoustic broadcast)• No on-board computer• Molecular positional device (robotic arm)• Liquid environment: solvent and three

feedstock molecules• Able to synthesize most stiff hydrocarbons

(diamond, graphite, buckytubes, etc)

Broadcast replication

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A hydrocarbon bearing

HC assembler

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A hydrocarbon universal joint

HC assembler

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A hydrogen abstraction tool

http://www.zyvex.com/nanotech/Habs/Habs.html

Molecular tools

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Exponential assembly

Broadcast replication

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Elements in exponential assembly

• No on-board instructions (electronic broadcast)• External X, Y and Z (mechanical broadcast)• No on-board computer• MEMS positional device (2 DOF robotic arm)• Able to assemble appropriate lithographically

manufactured parts pre-positioned on a surface in air

Broadcast replication

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• Functionality can be moved from the replicating component to the environment

• On-board / off board instructions and computation

• Positional assembly at different size scales• Very few systematic investigations of the

wide diversity of replicating systems

Take home message: the diversity of replicating systems is enormous

Replication

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An overview of replicating systemsfor manufacturing

• Advanced Automation for Space Missions, edited by Robert Freitas and William Gilbreath NASA Conference Publication 2255, 1982

• A web page with an overview of replication: http://www.zyvex.com/nanotech/selfRep.html

Replication

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• The term “self replication” carries assumptions and connotations (mostly derived from biological systems) that are grossly incorrect or misleading when applied to many replicating systems (broadcast systems such as the HC assembler and Rotapod, as well as many others)

Terminology

Replication

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• be like living systems• be adaptable (survive in natural environment) • be very complex• have on-board instructions• be self sufficient (uses only very simple parts)

Popular misconceptions:replicating systems must

Replication

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• Fear of self replicating systems is based largely on misconceptions

• Misplaced fear could block research• And prevent a deeper understanding of

systems that might pose serious concerns• Foresight Guidelines address the safety

issues

Misconceptions are harmful

Replication

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• Advances in technology can greatly reduce human suffering

• Informed decisions require research, uninformed decisions can be dangerous

• A 99.99% effective ban means the unregulated 0.01% will develop and deploy the technology

Research is a good ideabanning research is a bad idea

Replication

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• Development and analysis of more replicating architectures (convergent assembly, others)

• Systematic study of existing proposals• Education of the scientific community and

the general public

What is needed

Replication

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Self replication

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);}

A C program that prints outan exact copy of itself

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Self replication

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

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

English translation:

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kTkb2

σ: mean positional error k: restoring forcekb: Boltzmann’s constantT: temperature

Classical uncertainty

The Vision

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kTkb2

σ: 0.02 nm (0.2 Å) k: 10 N/mkb: 1.38 x 10-23 J/KT: 300 K

Classical uncertainty

The Vision

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Proposal for amolecular robotic arm

The Vision

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Arranging Molecular Building Blocks (MBBs) with SPMs

• Picking up, moving, and putting down a molecule has only recently been accomplished

• Stacking MBBs with an SPM has yet to be done

Positional assembly

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Designing MBBs and SPM tips

• The next step is to design an MBB/SPM tip combination that lets us pick up, move, put down, stack and unstack the MBBs

• A wide range of candidate MBBs are possible

Positional assembly

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http://www.zyvex.com/nanotech/selfRep.html

Complexity ofself replicating systems (bits)

• Mycoplasma genitalia 1,160,140• Drexler’s assembler 100,000,000• Human 6,400,000,000

The Vision

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Approach

H. J. Lee and W. Ho, SCIENCE 286, p. 1719, NOVEMBER 1999

Manipulation and bond formation by STM

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Approach

Saw-Wai Hla et al., Physical Review Letters 85, 2777-2780, September 25 2000

Manipulation and bond formation by STM

I I

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Property Diamond’s value Comments

Chemical reactivity Extremely low

Hardness (kg/mm2) 9000 CBN: 4500 SiC: 4000

Thermal conductivity (W/cm-K) 20 Ag: 4.3 Cu: 4.0

Tensile strength (pascals) 3.5 x 109 (natural) 1011 (theoretical)

Compressive strength (pascals) 1011 (natural) 5 x 1011 (theoretical)

Band gap (ev) 5.5 Si: 1.1 GaAs: 1.4

Resistivity (W-cm) 1016 (natural)

Density (gm/cm3) 3.51

Thermal Expansion Coeff (K-1) 0.8 x 10-6 SiO2: 0.5 x 10-6

Refractive index 2.41 @ 590 nm Glass: 1.4 - 1.8

Coeff. of Friction 0.05 (dry) Teflon: 0.05

Source: Crystallume

ApproachWhat to make:Diamond Physical Properties

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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.

Molecular tools

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Some other molecular toolsMolecular tools

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A synthetic strategy for the synthesis of diamondoid structures

• Positional assembly (6 degrees of freedom)• Highly reactive compounds (radicals,

carbenes, etc)• Inert environment (vacuum, noble gas) to

eliminate side reactions

Molecular tools