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Whither nanotechnology?

Ralph C. MerkleDistinguished Professor of Computing

Georgia Tech College of Computing

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Web pages

www.foresight.org

www.zyvex.com/nano

www.nano.gov

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Health, wealth and atoms

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Arranging atoms

• Flexibility• Precision• Cost

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Richard Feynman,1959

There’s plenty of roomat the bottom

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1980’s, 1990’s

First STMBy Binnig and Rohrer

Experiment and theory

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President Clinton, 2000

“Imagine the possibilities: materials with ten times the strength of steel and only a small fraction of the weight -- shrinking all the information housed at the Library of Congress into a device the size of a sugar cube -- detecting cancerous tumors when they are only a few cells in size.”

The National Nanotechnology Initiative

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Arrangements of atoms

.

Today

The goal

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The goal

.

The goal

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Positional assembly

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

Experimental

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Theoretical

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• Manufacturing is about moving atoms

• Molecular mechanics studies the motions of atoms

• Molecular mechanics is based on the Born-Oppenheimer approximation

Molecular mechanics

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The carbon nucleus has a mass over 20,000 times that of the electron

• Moves slower

• Positional uncertainty smaller

Born-Oppenheimer

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• Treat nuclei as point masses

• Assume ground state electrons

• Then the energy of the system is fully determined by the nuclear positions

• Directly approximate the energy from the nuclear positions, and we don’t even have to compute the electronic structure

Born-Oppenheimer

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Internuclear distance

Ene

rgy

Hydrogen molecule: H2

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Hydrocarbon machines

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Molecular machines

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Theoretical

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kTkb2

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

Thermal noise

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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

Thermal noise

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Property Diamond’s value Comments

Chemical reactivity Extremely lowHardness (kg/mm2) 9000 CBN: 4500 SiC: 4000Thermal conductivity (W/cm-K) 20 Ag: 4.3 Cu: 4.0Tensile 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: 1.4Resistivity (W-cm) 1016 (natural)Density (gm/cm3) 3.51Thermal Expansion Coeff (K-1) 0.8 x 10-6 SiO2: 0.5 x 10-6

Refractive index 2.41 @ 590 nm Glass: 1.4 - 1.8Coeff. of Friction 0.05 (dry) Teflon: 0.05

Source: Crystallume

Diamond physical properties

What to make

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Making diamond today

Illustration courtesy of P1 Diamond Inc.

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Hydrogen abstraction tool

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Other molecular tools

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Some journal publications•Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated Growth of Nanocrystalline Diamond C(110) Surface, J. Comp. Theor. Nanosci. 1(March 2004), Jingping Peng, Robert A. Freitas Jr., Ralph C. Merkle. In press. •Theoretical Analysis of Diamond Mechanosynthesis. Part II. C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools, J. Comp. Theor. Nanosci. 1(March 2004). David J. Mann, Jingping Peng, Robert A. Freitas Jr., Ralph C. Merkle, In press. •Theoretical analysis of a carbon-carbon dimer placement tool for diamond mechanosynthesis, Ralph C. Merkle and Robert A. Freitas Jr., J. Nanosci. Nanotechnol. 3 June 2003. (Abstract) •A proposed "metabolism" for a hydrocarbon assembler, Nanotechnology 8 (1997) pages 149-162. •Theoretical studies of reactions on diamond surfaces, by S.P. Walch and R.C. Merkle, Nanotechnology 9 (1998) pages 285-296.•Theoretical studies of a hydrogen abstraction tool for nanotechnology, by Charles Musgrave, Jason Perry, Ralph C. Merkle and William A. Goddard III; Nanotechnology 2 (1991) pages 187-195.

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Self replication

A redwood tree(sequoia sempervirens)112 meters tallRedwood National Park

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

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The Von Neumann architecture

UniversalComputer

UniversalConstructor

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

Self replication

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

Drexler’s proposal for an assembler

Self replication

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Exponential assembly

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Convergent assembly

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Kinematic Self-Replicating Machines (Landes Bioscience, 2004, in review).

Reviews the voluminous theoretical and experimental literature about physical self-replicating systems.

Freitas and Merkle

Self replication

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• Today: potatoes, lumber, wheat, etc. are all about a dollar per kilogram.

• Tomorrow: almost any product will be about a dollar per kilogram or less. (Design costs, licensing costs, etc. not included)

Replication

Manufacturing costsper kilogramwill be low

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The impactof a new manufacturing technologydepends on what you make

Impact

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• We’ll have more computing power in the volume of a sugar cube than the sum total of all the computer power that exists in the world today

• More than 1021 bits in the same volume• Almost a billion Pentiums in parallel

Powerful Computers

Impact

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• New, inexpensive materials with a strength-to-weight ratio over 50 times that of steel

• Critical for aerospace: airplanes, rockets, satellites…

• Useful in cars, trucks, ships, ...

Lighter, stronger,smarter, less expensive

Impact

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• 50x reduction of structural mass

• Cost per kilogram under a dollar

• Reducing cost to low earth orbit by 1,000 or more

Impact

http://science.nas.nasa.gov/Groups/Nanotechnology/publications/1997/applications/

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Mitochondrion~1-2 by 0.1-0.5 microns

Size of a robotic arm~100 nanometers

Impact

8-bit computer

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“Typical” cell: ~20 microns

MitochondrionSize of a robotic

arm ~100 nanometers

Scale

8-bit computer

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Provide oxygen

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Digest bacteria

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Digest bacteria

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• Surveys medical applications of nanotechnology

• Volume I (of three) published in 1999• Robert Freitas, Zyvex

Survey of the field

Nanomedicine

http://www.foresight.org/Nanomedicine

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Military applications of molecular manufacturing have even greater potential than nuclear weapons to radically change the balance of power.

http://www.zyvex.com/nanotech/nano4/jeremiahPaper.html

Global Security

Admiral David E. Jeremiah, USN (Ret)

Former Vice Chairman, Joint Chiefs of Staff

November 9, 1995

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Core molecularmanufacturingcapabilities

Today ProductsProducts

Products

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Products

ProductsProducts

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ProductsProducts

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ProductsProducts

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Products

Overview

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• Correct scientific answer: I don’t know• Trends in computer hardware suggestive• Beyond typical 3-5 year planning horizon• Depends on what we do• Babbage’s computer designed in 1830’s

How long?

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Research objectives• Mechanosynthesis

H abstraction, Carbene insertion, …• System design

assemblers, robotic arms, …

Goals

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Nanotechnology offers ... possibilities for health, wealth, and capabilities beyond most past imaginings.

K. Eric Drexler

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σ2: positional variance

k: restoring force

m: mass of particle

ħ: Planck’s constant divided by 2π

km22

Quantum uncertainty

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• C-C spring constant: k~440 N/m

• Typical C-C bond length: 0.154 nm• σ for C in single C-C bond: 0.004 nm• σ for electron (same k): 0.051 nm

Quantum uncertainty

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• Internuclear distance for bonds

• Angle (as in H2O)

• Torsion (rotation about a bond, C2H6)

• Internuclear distance for van der Waals

• Spring constants for all of the above

• More terms used in many models

• Quite accurate in domain of parameterization

Molecular mechanics

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• Limited ability to deal with excited states• Tunneling (actually a consequence of the

point-mass assumption)• Rapid nuclear movements reduce accuracy• Large changes in electronic structure

caused by small changes in nuclear position reduce accuracy

Molecular mechanics

Limitations

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Buckyballs

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Buckytubes

FullerenesSWNTMWNTChiralityBuckminsterfullerenes

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Buckytubes

What is “chirality?”

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

Macroscopiccomputer

Molecularconstructor

Molecularconstructor

Molecularconstructor

Broadcast architecture

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Nanopores

Illustration from Harvard Nanopore Group

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Millipede

Illustration from IBM Zurich

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Minimal assembler

YX

Z

Z

X

Y

X > Y > Z

Materials TransportMechanisms

AcousticTransducer

Piston

GranddaughterBase Plate Daughter

Base Plate

ParentBase Plate

“I/O” Wall

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System

Sub-systemSub-systemSub-system

part part part part part part

System designs

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Why don’t we have more system designs?

System designs

Development times are 10+ yearsPlanning horizons are usually 10- yearsResearch funding focused on “science”FUD

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• Shorten development times• Identify intermediate targets• Gain support from groups with long planning

horizons• Lengthen planning horizons• Reduce FUD by detailed design and

analysis

What to do

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3

4

4

3k

L

Er

E: Young’s modulusk: transverse stiffnessr: radiusL: length

Stiffness

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3

4

4

3k

L

Er

E: 1012 N/m2

k: 10 N/mr: 8 nmL: 100 nm

Stiffness

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Convergent assembly

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Convergent assembly

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Convergent assembly

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• SSTO (Single Stage To Orbit) vehicle

• 3,000 kg total mass (including fuel)

• 60 kilogram structural mass

• 500 kg for four passengers with luggage, air, seating, etc.

• Liquid oxygen, hydrogen

• Cost: a few thousand dollars

Space

K. Eric Drexler, Journal of the British Interplanetary Society,V 45, No 10, pp 401-405 (1992).Molecular manufacturing for space systems: an overview

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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