Transcript Long and medium term goals in molecular nanotechnology

Long and medium term goals
in molecular nanotechnology
Ralph C. Merkle
Xerox PARC
www.merkle.com
Fifth Foresight Conference on
Molecular Nanotechnology
November 5-8
Palo 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 an
attempt to violate any laws; it is something, in
principle, that can be done; but in practice, it
has not been done because we are too
big.
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
What we can make today
(not to scale)
.
The goal of molecular
nanotechnology:
a healthy bite.
.
Two ways to
create 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.
If the target is “close” to what we
can make, the evolutionary method
can be quite effective.
Target
..
What we can make today
(not to scale)
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)
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
Today
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
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
Universal
Computer
Universal
Constructor
Complexity of self replicating systems
(bits)
Von Neumann's universal constructorabout 500,000
Internet worm (Robert Morris, Jr., 1988)
500,000
Mycoplasma capricolum
1,600,000
E. Coli
8,000,000
Drexler's assembler
100,000,000
Human
6,400,000,000
NASA Lunar
Manufacturing Facility over 100,000,000,000
http://nano.xerox.com/nanotech/selfRep.html
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
Molecular
computer
Molecular
constructor
Positional device
Tip chemistry
The broadcast architecture
Molecular
constructor
Molecular
constructor
Macroscopic
computer
Molecular
constructor
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
External
gas
Actuator
(under tension)
Compressed gas
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 Missions
Proceedings 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 the
simple 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 selfassembly 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
c
| and |
x
y
join the two struts
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.
Can today’s molecular motors be
modified so they can be
controllably stepped?
•
•
•
•
Chemical signals
Acoustic signals
Optical (photochemical) signals
Other
Today
Overview of the
development of
molecular
nanotechnology
Produc
Products
Core molecular
Products
Products
manufacturing
Products
capabilities
Products Products
Products
Products
Products Products
Products Products
Products
Products
Products
Products
Products
Products
Products
Products
Produc
Products
Products Products
Products
The problems of chemistry and biology
can be greatly helped if our ability to see
what we are doing, and
to 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