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Overview of Nanotechnology
(not "Just the FAQs")

Adapted by J.Storrs Hall from papers by Ralph C. Merkle and K. Eric Drexler

INTRODUCTION

Nanotechnology is an anticipated manufacturing technology giving thorough,
inexpensive control of the structure of matter. The term has sometimes been
used to refer to any technique able to work at a submicron scale; Here on
sci.nanotech we are interested in what is sometimes called molecular
nanotechnology, which means basically "A place for every atom and every
atom in its place."  (other terms, such as molecular engineering, molecular
manufacturing, etc. are also often applied).

Molecular manufacturing will enable the construction of giga-ops computers
smaller than a cubic micron; cell repair machines; personal manufacturing
and recycling appliances; and much more.

NANOTECHNOLOGY

Broadly speaking, the central thesis of nanotechnology is that almost any
chemically stable structure that can be specified can in fact be built.
This possibility was first advanced by Richard Feynman in 1959 [4] when he
said: "The principles of physics, as far as I can see, do not speak against
the possibility of maneuvering things atom by atom."  (Feynman won the 1965
Nobel prize in physics).

This concept is receiving increasing attention in the research community.
There have been two international conferences directly on molecular
nanotechnology[30,31] as well as a broad range of conferences on related
subjects.  Science [23, page 26] said "The ability to design and
manufacture devices that are only tens or hundreds of atoms across promises
rich rewards in electronics, catalysis, and materials.  The scientific
rewards should be just as great, as researchers approach an ultimate level
of control - assembling matter one atom at a time."  "Within the decade,
[John] Foster [at IBM Almaden] or some other scientist is likely to learn
how to piece together atoms and molecules one at a time using the STM
[Scanning Tunnelling Microscope]."

Eigler and Schweizer[25] at IBM reported on "...the use of the STM at low
temperatures (4 K) to position individual xenon atoms on a single- crystal
nickel surface with atomic precision.  This capacity has allowed us to
fabricate rudimentary structures of our own design, atom by atom.  The
processes we describe are in principle applicable to molecules also. ..."

ASSEMBLERS

Drexler[1,8,11,19,32] has proposed the "assembler", a device having a
submicroscopic robotic arm under computer control. It will be capable of
holding and positioning reactive compounds in order to control the precise
location at which chemical reactions take place.  This general approach
should allow the construction of large atomically precise objects by a
sequence of precisely controlled chemical reactions, building objects
molecule by molecule.  If designed to do so, assemblers will be able to
build copies of themselves, that is, to replicate.

Because they will be able to copy themselves, assemblers will be
inexpensive. We can see this by recalling that many other products of
molecular machines--firewood, hay, potatoes--cost very little. By working
in large teams, assemblers and more specialized nanomachines will be able
to build objects cheaply. By ensuring that each atom is properly placed,
they will manufacture products of high quality and reliability. Left-over
molecules would be subject to this strict control as well, making the
manufacturing process extremely clean.

     Ribosomes

The plausibility of this approach can be illustrated by the ribosome.
Ribosomes manufacture all the proteins used in all living things on this
planet.  A typical ribosome is relatively small (a few thousand cubic
nanometers) and is capable of building almost any protein by stringing
together amino acids (the building blocks of proteins) in a precise linear
sequence.  To do this, the ribosome has a means of grasping a specific
amino acid (more precisely, it has a means of selectively grasping a
specific transfer RNA, which in turn is chemically bonded by a specific
enzyme to a specific amino acid), of grasping the growing polypeptide, and
of causing the specific amino acid to react with and be added to the end of
the polypeptide[9].

The instructions that the ribosome follows in building a protein are
provided by mRNA (messenger RNA).  This is a polymer formed from the four
bases adenine, cytosine, guanine, and uracil.  A sequence of several
hundred to a few thousand such bases codes for a specific protein.  The
ribosome "reads" this "control tape" sequentially, and acts on the
directions it provides.

     Assemblers

In an analogous fashion, an assembler will build an arbitrary molecular
structure following a sequence of instructions.  The assembler, however,
will provide three-dimensional positional and full orientational control
over the molecular component (analogous to the individual amino acid) being
added to a growing complex molecular structure (analogous to the growing
polypeptide).  In addition, the assembler will be able to form any one of
several different kinds of chemical bonds, not just the single kind (the
peptide bond) that the ribosome makes.

Calculations indicate that an assembler need not inherently be very large.
Enzymes "typically" weigh about 10^5 amu (atomic mass units).  while the
ribosome itself is about 3 x 10^6 amu[9].  The smallest assembler might be
a factor of ten or so larger than a ribosome.  Current design ideas for an
assembler are somewhat larger than this: cylindrical "arms" about 100
nanometers in length and 30 nanometers in diameter, rotary joints to allow
arbitrary positioning of the tip of the arm, and a worst-case positional
accuracy at the tip of perhaps 0.1 to 0.2 nanometers, even in the presence
of thermal noise.  Even a solid block of diamond as large as such an arm
weighs only sixteen million amu, so we can safely conclude that a hollow
arm of such dimensions would weigh less.  Six such arms would weigh less
than 10^8 amu.

     Molecular Computers

The assembler requires a detailed sequence of control signals, just as the
ribosome requires mRNA to control its actions.  Such detailed control
signals can be provided by a computer.  A feasible design for a molecular
computer has been presented by Drexler[2,11].  This design is mechanical in
nature, and is based on sliding rods that interact by blocking or
unblocking each other at "locks."  This design has a size of about 5 cubic
nanometers per "lock" (roughly equivalent to a single logic gate).
Quadrupling this size to 20 cubic nanometers (to allow for power,
interfaces, and the like) and assuming that we require a minimum of 10^4
"locks" to provide minimal control results in a volume of 2 x 10^5 cubic
nanometers (.0002 cubic microns) for the computational element.  (This many
gates is sufficient to build a simple 4-bit or 8-bit general purpose
computer, e.g. a 6502).

An assembler might have a kilobyte of high speed (rod-logic based) RAM,
(similar to the amount of RAM used in a modern one-chip computer) and 100
kilobytes of slower but more dense "tape" storage - this tape storage would
have a mass of 10^8 amu or less (roughly 10 atoms per bit - see below).
Some additional mass will be used for communications (sending and receiving
signals from other computers) and power.  In addition, there will probably
be a "toolkit" of interchangable tips that can be placed at the ends of the
assembler's arms.  When everything is added up a small assembler, with
arms, computer, "toolkit," etc. should weigh less than 10^9 amu.

Escherichia coli (a common bacterium) weigh about 10^12 amu[9, page 123].
Thus, an assembler should be much larger than a ribosome, but much smaller
than a bacterium.

     Self Replicating Systems

It is also interesting to compare Drexler's architecture for an assembler
with the Von Neumann architecture for a self replicating device.  Von
Neumann's "universal constructing automaton"[21] had both a universal
Turing machine to control its functions and a "constructing arm" to build
the "secondary automaton."  The constructing arm can be positioned in a
two-dimensional plane, and the "head" at the end of the constructing arm is
used to build the desired structure.  While Von Neumann's construction was
theoretical (existing in a two dimensional cellular automata world), it
still embodied many of the critical elements that now appear in the
assembler.

Should we be concerned about runaway replicators?  It would be hard to
build a machine with the wonderful adaptability of living organisms.  The
replicators easiest to build will be inflexible machines, like automobiles
or industrial robots, and will require special fuels and raw materials, the
equivalents of hydraulic fluid and gasoline. To build a runaway replicator
that could operate in the wild would be like building a car that could go
off-road and fuel itself from tree sap. With enough work, this should be
possible, but it will hardly happen by accident. Without replication,
accidents would be like those of industry today: locally harmful, but not
catastrophic to the biosphere. Catastrophic problems seem more likely to
arise though deliberate misuse, such as the use of nanotechnology for
military aggression.

     Positional Chemistry

Chemists have been remarkably successful at synthesizing a wide range of
compounds with atomic precision.  Their successes, however, are usually
small in size (with the notable exception of various polymers).  Thus, we
know that a wide range of atomically precise structures with perhaps a few
hundreds of atoms in them are quite feasible.  Larger atomically precise
structures with complex three-dimensional shapes can be viewed as a
connected sequence of small atomically precise structures.  While chemists
have the ability to precisely sculpt small collections of atoms there is
currently no ability to extend this capability in a general way to
structures of larger size.  An obvious structure of considerable scientific
and economic interest is the computer.  The ability to manufacture a
computer from atomically precise logic elements of molecular size, and to
position those logic elements into a three- dimensional volume with a
highly precise and intricate interconnection pattern would have
revolutionary consequences for the computer industry.

A large atomically precise structure, however, can be viewed as simply a
collection of small atomically precise objects which are then linked
together.  To build a truly broad range of large atomically precise objects
requires the ability to create highly specific positionally controlled
bonds.  A variety of highly flexible synthetic techniques have been
considered in [32].  We shall describe two such methods here to give the
reader a feeling for the kind of methods that will eventually be feasible.

We assume that positional control is available and that all reactions take
place in a hard vacuum.  The use of a hard vacuum allows highly reactive
intermediate structures to be used, e.g., a variety of radicals with one or
more dangling bonds.  Because the intermediates are in a vacuum, and
because their position is controlled (as opposed to solutions, where the
position and orientation of a molecule are largely random), such radicals
will not react with the wrong thing for the very simple reason that they
will not come into contact with the wrong thing.

Normal solution-based chemistry offers a smaller range of controlled
synthetic possibilities.  For example, highly reactive compounds in
solution will promptly react with the solution.  In addition, because
positional control is not provided, compounds randomly collide with other
compounds.  Any reactive compound will collide randomly and react randomly
with anything available.  Solution-based chemistry requires extremely
careful selection of compounds that are reactive enough to participate in
the desired reaction, but sufficiently non-reactive that they do not
accidentally participate in an undesired side reaction.  Synthesis under
these conditions is somewhat like placing the parts of a radio into a box,
shaking, and pulling out an assembled radio.  The ability of chemists to
synthesize what they want under these conditions is amazing.

Much of current solution-based chemical synthesis is devoted to preventing
unwanted reactions.  With assembler-based synthesis, such prevention is a
virtually free by-product of positional control.

To illustrate positional synthesis in vacuum somewhat more concretely, let
us suppose we wish to bond two compounds, A and B.  As a first step, we
could utilize positional control to selectively abstract a specific
hydrogen atom from compound A.  To do this, we would employ a radical that
had two spatially distinct regions: one region would have a high affinity
for hydrogen while the other region could be built into a larger "tip"
structure that would be subject to positional control.  A simple example
would be the 1-propynyl radical, which consists of three co-linear carbon
atoms and three hydrogen atoms bonded to the sp3 carbon at the "base" end.
The radical carbon at the radical end is triply bonded to the middle
carbon, which in turn is singly bonded to the base carbon.  In a real
abstraction tool, the base carbon would be bonded to other carbon atoms in
a larger diamondoid structure which provides positional control, and the
tip might be further stabilized by a surrounding "collar" of unreactive
atoms attached near the base that would prevent lateral motions of the
reactive tip.

The affinity of this structure for hydrogen is quite high.  Propyne (the
same structure but with a hydrogen atom bonded to the "radical" carbon) has
a hydrogen-carbon bond dissociation energy in the vicinity of 132
kilocalories per mole.  As a consequence, a hydrogen atom will prefer being
bonded to the 1-propynyl hydrogen abstraction tool in preference to being
bonded to almost any other structure.  By positioning the hydrogen
abstraction tool over a specific hydrogen atom on compound A, we can
perform a site specific hydrogen abstraction reaction.  This requires
positional accuracy of roughly a bond length (to prevent abstraction of an
adjacent hydrogen).  Quantum chemical analysis of this reaction by Musgrave
et. al.[41] show that the activation energy for this reaction is low, and
that for the abstraction of hydrogen from the hydrogenated diamond (111)
surface (modeled by isobutane) the barrier is very likely zero.

Having once abstracted a specific hydrogen atom from compound A, we can
repeat the process for compound B.  We can now join compound A to compound
B by positioning the two compounds so that the two dangling bonds are
adjacent to each other, and allowing them to bond.

This illustrates a reaction using a single radical.  With positional
control, we could also use two radicals simultaneously to achieve a
specific objective.  Suppose, for example, that two atoms A1 and A2 which
are part of some larger molecule are bonded to each other.  If we were to
position the two radicals X1 and X2 adjacent to A1 and A2, respectively,
then a bonding structure of much lower free energy would be one in which
the A1-A2 bond was broken, and two new bonds A1-X1 and A2-X2 were formed.
Because this reaction involves breaking one bond and making two bonds
(i.e., the reaction product is not a radical and is chemically stable) the
exact nature of the radicals is not critical.  Breaking one bond to form
two bonds is a favored reaction for a wide range of cases.  Thus, the
positional control of two radicals can be used to break any of a wide range
of bonds.

A range of other reactions involving a variety of reactive intermediate
compounds (carbenes are among the more interesting ones) are proposed in
[32], along with the results of semi-empirical and ab initio quantum
calculations and the available experimental evidence.

Another general principle that can be employed with positional synthesis is
the controlled use of force.  Activation energy, normally provided by
thermal energy in conventional chemistry, can also be provided by
mechanical means.  Pressures of 1.7 megabars have been achieved
experimentally in macroscopic systems[43].  At the molecular level such
pressure corresponds to forces that are a large fraction of the force
required to break a chemical bond.  A molecular vise made of hard
diamond-like material with a cavity designed with the same precision as the
reactive site of an enzyme can provide activation energy by the extremely
precise application of force, thus causing a highly specific reaction
between two compounds.

To achieve the low activation energy needed in reactions involving radicals
requires little force, allowing a wider range of reactions to be caused by
simpler devices (e.g., devices that are able to generate only small force).
Further analysis is provided in [32].

Feynman said: "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."  Drexler has provided the substantive analysis required before
this objective can be turned into a reality.  We are nearing an era when we
will be able to build virtually any structure that is specified in atomic
detail and which is consistent with the laws of chemistry and physics.
This has substantial implications for future medical technologies and
capabilities.

     Cost

One consequence of the existence of assemblers is that they are cheap.
Because an assembler can be programmed to build almost any structure, it
can in particular be programmed to build another assembler.  Thus, self
reproducing assemblers should be feasible and in consequence the
manufacturing costs of assemblers would be primarily the cost of the raw
materials and energy required in their construction.  Eventually (after
amortization of possibly quite high development costs), the price of
assemblers (and of the objects they build) should be no higher than the
price of other complex structures made by self-replicating systems.
Potatoes - which have a staggering design complexity involving tens of
thousands of different genes and different proteins directed by many
megabits of genetic information - cost well under a dollar per pound.

PATHWAYS TO NANOTECHNOLOGY

The three paths of protein design (biotechnology), biomimetic chemistry,
and atomic positioning are parts of a broad bottom up strategy: working at
the molecular level to increase our ability to control matter. Traditional
miniaturization efforts based on microelectronics technology have reached
the submicron scale; these can be characterized as the top down strategy.
The bottom-up strategy, however, seems more promising.

INFORMATION

More information on nanotechnology can be found in these books
(all by Eric Drexler (and various co-authors)):

Engines of Creation (Anchor, 1986)      ISBN: 0-385-19972-2

   This book was the definition of the original charter
   of sci.nanotech.  Popularly written, it introduces
   assemblers, and discusses the various social and
   technical implications nanotechnology might have.

Unbounding the Future (Morrow, 1991)       0-688-09124-5

   Essentially an update of Engines, with a better low-level
   description of how nanomachines might work, and less
   speculation on space travel, cryonics, etc.

Nanosystems (Wiley, 1992)                  0-471-57518-6

   This is the technical book that grew out of Drexler's
   PhD thesis.  It is a real tour de force that provides a
   *substantial* theoretical background for nanotech ideas.


The Foresight Institute publishes on both technical and nontechnical
issues in nanotechnology. For example, students may write for their
free Briefing #1, "Studying Nanotechnology". The Foresight Institute's
main publications are the Update newsletter and Background essay
series.  The Update newsletter includes both policy discussions and a
technical column enabling readers to find material of interest in the
recent scientific literature.  These publications appear on
sci.nanotech on a delayed basis. To receive them in timely fashion and
paper form, send a donation of twenty-five dollars or more to:

    The Foresight Institute, Department U
    P.O. Box 61058
    Palo Alto, CA 94306 USA

A set of papers and the archives of sci.nanotech can be had by standard
anonymous FTP to planchet.rutgers.edu.

Sci.nanotech is moderated and is intended to be of a technical nature.

--JoSH (moderator)

REFERENCES

[Not all of these are referred to in the text, but they are of
 interest nevertheless.]

1.     "Engines of Creation" by K. Eric Drexler, Anchor Press, 1986.

2.     "Nanotechnology:  wherein molecular computers control tiny
circulatory submarines", by A. K. Dewdney, Scientific American, January
1988, pages 100 to 103.

3.     "Foresight Update", a publication of the Foresight Institute, Box
61058, Palo Alto, CA 94306.

4.     "There's Plenty of Room at the Bottom" a talk by Richard Feynman
(awarded the Nobel Prize in Physics in 1965) at an annual meeting of the
American Physical Society given on December 29, 1959.  Reprinted in
"Miniaturization", edited by H. D. Gilbert (Reinhold, New York, 1961)
pages 282-296.

5.     "Scanning Tunneling Microscopy and Atomic Force Microscopy:
Application to Biology and Technology" by P. K. Hansma, V. B. Elings, O.
Marti, and C. E. Bracker.  Science, October 14 1988, page 209-216.

6.     "Molecular manipulation using a tunnelling microscope," by J. S.
Foster, J. E. Frommer and P. C. Arnett.  Nature, Vol. 331 28 January
1988, pages 324-326.

7.     "The fundamental physical limits of computation" by Charles H.
Bennet and Rolf Landauer, Scientific American Vol. 253, July 1985, pages
48-56.

8.     "Molecular Engineering:  An Approach to the Development of General
Capabilities for Molecular Manipulation," by K. Eric Drexler,
Proceedings of the National Academy of Sciences (USA), Vol 78, pp 5275-
78, 1981.

9.     "Molecular Biology of the Gene", fourth edition, by James D.
Watson, Nancy H. Hopkins, Jeffrey W. Roberts, Joan Argetsinger Steitz,
and Alan M. Weiner.  Benjamin Cummings, 1987.  It can now be purchased
as a single large volume.

10.     "Tiny surgical robot being developed", San Jose Mercury News, Feb.
18, 1989, page 26A

11.     "Rod Logic and Thermal Noise in the Mechanical Nanocomputer", by
K. Eric Drexler, Proceedings of the Third International Symposium on
Molecular Electronic Devices, F. Carter ed., Elsevier 1988.

12.     "Submarines small enough to cruise the bloodstream", in Business
Week, March 27 1989, page 64.

13.     "Conservative Logic", by Edward Fredkin and Tommaso Toffoli,
International Journal of Theoretical Physics, Vol. 21 Nos. 3/4, 1982,
pages 219-253.

14.     "The Tomorrow Makers", Grant Fjermedal, MacMillan 1986.

15.     "Dissipation and noise immunity in computation and communication"
by Rolf Landauer, Nature, Vol. 335, October 27 1988, page 779.

16.     "Notes on the History of Reversible Computation" by Charles H.
Bennett, IBM Journal of Research and Development, Vol. 32, No. 1,
January 1988.

17.     "Classical and Quantum Limitations on Energy Consumption in
Computation" by K. K. Likharev, International Journal of Theoretical
Physics, Vol. 21, Nos. 3/4, 1982.

18.     "Principles and Techniques of Electron Microscopy: Biological
Applications," Third edition, by M. A. Hayat, CRC Press, 1989.

19.     "Machines of Inner Space" by K. Eric Drexler, 1990 Yearbook of
Science and the Future, pages 160-177, published by Encyclopedia
Britannica, Chicago 1989.

20.     "Reversible Conveyer Computation in Array of Parametric Quantrons"
by K. K. Likharev, S. V. Rylov, and V. K. Semenov, IEEE Transactions on
Magnetics, Vol. 21 No. 2, March 1985, pages 947-950

21.     "Theory of Self Reproducing Automata" by John Von Neumann, edited
by Arthur W. Burks,  University of Illinois Press, 1966.

22.     "The Children of the STM" by Robert Pool, Science, Feb. 9, 1990,
pages 634-636.

23.     "A Small Revolution Gets Under Way," by Robert Pool, Science, Jan.
5 1990.

24.     "Advanced Automation for Space Missions", Proceedings of the 1980
NASA/ASEE Summer Study, edited by Robert A. Freitas, Jr. and William P.
Gilbreath.  Available from NTIS, U.S. Department of Commerce, National
Technical Information Service, Springfield, VA 22161; telephone 703-487-
4650, order no. N83-15348

25.     "Positioning Single Atoms with a Scanning Tunnelling Microscope,"
by D. M. Eigler and E. K. Schweizer, Nature Vol 344, April 5 1990, page
524-526.

26.     "Mind Children" by Hans Moravec, Harvard University Press, 1988.

27.     "Microscopy of Chemical-Potential Variations on an Atomic Scale"
by C.C. Williams and H.K. Wickramasinghe, Nature, Vol 344, March 22
1990, pages 317-319.

28.     "Time/Space Trade-Offs for Reversible Computation" by Charles H.
Bennett, SIAM J. Computing, Vol. 18, No. 4, pages 766-776, August 1989.

29.     "Fixation for Electron Microscopy" by M. A. Hayat, Academic Press,
1981.

30.     "Nonexistent technology gets a hearing," by I. Amato, Science
News, Vol. 136, November 4, 1989, page 295.

31.     "The Invisible Factory,"  The Economist, December 9, 1989, page 91.

32.     "Nanosystems:  Molecular Machinery, Manufacturing and
Computation," by K. Eric Drexler, John Wiley 1992.

33.     "MITI heads for inner space" by David Swinbanks, Nature, Vol 346,
August 23 1990, page 688-689.

34.     "Fundamentals of Physics," Third Edition Extended, by David
Halliday and Robert Resnick, Wiley 1988.

35.     "General Chemistry" Second Edition, by Donald A. McQuarrie and
Peter A. Rock, Freeman 1987.

36.     "Charles Babbage On the Principles and Development of the
Calculator and Other Seminal Writings" by Charles Babbage and others.
Dover, New York, 1961.

37.     "Molecular Mechanics" by U. Burkert and N. L. Allinger, American
Chemical Society Monograph 177 (1982).

38.     "Breaking the Diffraction Barrier: Optical Microscopy on a
Nanometric Scale" by E. Betzig, J. K. Trautman, T.D. Harris, J.S.
Weiner, and R.L. Kostelak,  Science Vol. 251, March 22 1991, page 1468.

39.     "Two Types of Mechanical Reversible Logic," by Ralph C. Merkle,
submitted to Nanotechnology.

40.     "Atom by Atom, Scientists build 'Invisible' Machines of the
Future," Andrew Pollack, The New York Times, Science section, Tuesday
November 26, 1991, page B7.

41.     "Theoretical analysis of a site-specific hydrogen abstraction
tool," by Charles Musgrave, Jason Perry, Ralph C. Merkle and William A.
Goddard III, in Nanotechnology, April 1992.

42.     "Near-Field Optics: Microscopy, Spectroscopy, and Surface
Modifications Beyond the Diffraction Limit" by Eric Betzig and Jay K.
Trautman, Science, Vol. 257, July 10 1992, pages 189-195.

43.     "Guinness Book of World Records,"  Donald McFarlan et. al., Bantam
1989.