Long and medium term goals in molecular nanotechnology

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Long and medium term goals in molecular
nanotechnology

• Ralph C. Merkle
• Xerox PARC
• www.merkle.com

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Fifth Foresight Conference on Molecular
NanotechnologyNovember 5-8Palo Alto,
CAwww.foresight.org/Conferences
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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
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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
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Possible arrangements of atoms
What we can make today (not to scale)
.
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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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If the target is close to what we can make, the
evolutionary method can be quite effective.
What we can make today (not to scale)
Target
.
.
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Molecular Manufacturing
But there is every reason to believe that
molecular manufacturing systems are not close
to what we can make today.
.
What we can make today (not to scale)
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To develop tomorrows technology starting with
todays 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.

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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

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Products
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Core molecular manufacturing capabilities
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Overview of the development of molecular
nanotechnology
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• If you don't know where you are going, you will
  probably wind up somewhere else
• Laurence J Peter

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Two more fundamental ideas

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

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Von Neumann architecture for a self replicating
system
Universal Computer
Universal Constructor
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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 8,000,000 Drexler's assembler 100,00
0,000 Human 6,400,000,000 NASA
Lunar Manufacturing Facility over 100,000,000,000
http//nano.xerox.com/nanotech/selfRep.html
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A C program that prints out an exact copy of
itself

• main()char q34, n10,a"main() char
  q34,n10,acsc 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.ht
ml
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English translation

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

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Drexlers architecture for an assembler
Molecular computer
Molecular constructor
Positional device
Tip chemistry
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The broadcast architecture
Macroscopic computer
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Advantages of the broadcast architecture

• Simpler design
• Fewer parts
• Inherently safe

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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

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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).

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Simple pressure actuated device
External gas
Actuator (under tension)
Compressed gas
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A proposal for a molecular positional device
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A proposal for a molecular positional device
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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/hydroCarbonMetaboli
sm.html
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A simple binding site for butadiyne
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A hydrogen abstraction tool
http//nano.xerox.com/nanotech/Habs/Habs.html
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Some other molecular tools
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Synthesis of diamond todaydiamond 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.
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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

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A modest set of molecular tools should be
sufficient to synthesize most stiff hydrocarbons.
http//nano.xerox.com/nanotech/ hydroCarbonMetabol
ism.html
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• 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 Missions Proceedings
of the 1980 NASA/ASEE Summer Study
http//nano.xerox.com/nanotech/selfRepNASA.html
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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

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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

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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

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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

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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/li
  nk-chemistry.html

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Can we self assemble a robotic arm?
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Can we self assemble a Stewart platform?
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Can we self assemble an octahedron?
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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

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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.

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Sliding struts
ABCABCABCABCABCABCABCABCABCABCABCABC a
a a a
x x x x
XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ
a x
joins the two struts
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Sliding struts
ABCABCABCABCABCABCABCABCABCABCABCABC a c
a ca c a / / /
xy xy x y x
XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ
a x
c y
join the two struts
and
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Sliding struts
ABCABCABCABCABCABCABCABCABCABCABCABC c
c c c
y y y y
XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ
c y
Joins the two struts, which have now moved over
one unit.
Cycling through a-x, c-y and b-z produces
controlled relative motion of the two struts.
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Can todays molecular motors be modified so they
can be controllably stepped?

• Chemical signals
• Acoustic signals
• Optical (photochemical) signals
• Other

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Products
Products
Core molecular manufacturing capabilities
Products
Products
Products
Products
Products
Products
Products
Products
Products
Products
Products
Today
Products
Products
Products
Products
Products
Overview of the development of molecular
nanotechnology
Products
Products
Products
Products
Products
Products
Products
Products
52
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