Foresight Update 3
page 1
A publication of the Foresight Institute
 Nanometer
Molecule-Zapping
Steps toward controlling single chemical reactions
"One may now reasonably ask if it is possible to move and
alter matter predictably on an atomic scale…we have evidence
that we can remove a portion of a pinned molecule, effectively
performing transformations on single molecules using the
tunneling microscope," say John S. Foster, Jane E. Frommer,
and Patrick C. Arnett of IBM's Almaden
Research Center in a recent article in Nature[1].
The scanning tunneling microscope, as most of you know, is
conceptually quite simple. It uses a sharp,
electrically-conductive needle to scan a surface. The position of
the tip of the needle is controlled to within 0.1 ångstrom (less
than the radius of a hydrogen atom) using a voltage-controlled
piezo-electric drive. When the tip is within a few ångstroms of
the surface and a small voltage is applied to the needle, a
tunneling current flows from the tip to the surface. This
tunneling current is then detected and amplified, and can be used
to map the shape of the surface, much as a blind man's stick can
reveal the shape of an object.
In the new work, the surface is atomically smooth graphite with a
drop of dimethyl phthalate (a liquid) on its surface. (The type
of organic liquid does not seem critical; many other compounds
have been used.) The needle is electrochemically etched tungsten,
and is immersed in the liquid. Not only can the graphite surface
be imaged in the normal way, but a voltage pulse applied to the
needle (3.7 volts for 100 nanoseconds) can 'pin' one of the
organic molecules to the surface, where it can be viewed in the
normal fashion. A second voltage pulse applied at the same
location can remove the pinned molecule (though it often randomly
pins other molecules in an as-yet uncontrollable way). In some
cases, the voltage pulse will remove only part of the pinned
molecule, leaving behind a molecularly altered fragment.
The first application that comes to mind is a very high density
memory. The minimum spot-size demonstrated in the new work is 10
ångstroms, though a somewhat larger size might be required in
practice. If we assume that a single bit can be read or written
into a 10 ångstrom square, then a one square centimeter surface
can hold 1014 bits. That's one hundred terabytes. The
100 nanosecond pulse time sets a 10 megabit/second maximum write
rate, though this might be degraded for other reasons. At this
rate, it would take several months to a year of constant writing
to fill a one square centimeter memory. Access times will
probably be limited by the time needed to move the needle--which
might be a significant fraction of a second to travel one
centimeter--giving access times similar to those on current disk
drives. The manufacturing cost of such a system is unclear, but
the basic components do not seem unduly expensive. It seems safe
to predict that someone in the not-too-distant future is going to
build a low-cost very large capacity secondary storage
device (disk replacement) based on this technology.
The larger implication of this work, however, is that it may put
us on the threshold of controlled molecular manipulation. While
we can easily imagine more powerful techniques than poking at
objects with a sharpened stick (we clearly want a pair of
molecular-sized hands) the great virtue of this technique is that
we need not imagine it at all--it is real and is being pursued in
many laboratories. Even better, we can imagine incremental
improvements in this technique that ought to be
achievable--using, perhaps, two sharpened sticks
(chopsticks, anyone?) and shaping the tip of the stick in a more
refined and controlled way. The tip, viewed at the atomic scale,
is rather rough and there seems no reason why we cannot do
better--perhaps by examining and modifying one stick with the
other stick.
These larger implications have not been lost on the scientific
community--in an editorial on atomic-scale engineering in the
same issue of Nature, J. B. Pethica of the Oxford
Department of Materials Science says that the scanning tunneling
microscope has "…become one of the principle gedanken
tools for nanotechnology--the proposed direct manipulation of
matter, especially biological, on the atomic scale," and
"The work of Foster et al.[1] represents a significant
attempt at the much more important and difficult problem of the
direct manipulation of the structure of biological
materials."[2]
Dr. Ralph Merkle's interests range from neurophysiology to
computer security. He currently works in the latter field at
Xerox PARC.
References
- "Molecular Manipulation using a
Tunnelling Microscope," by J. S. Foster, J. E.
Frommer and P. C. Arnett; Nature, Vol. 331,
No. 28, 28 Jan. 1988, pp. 324-326.
- "Atomic Scale Engineering,"
by J. B. Pethica, op. cit. p. 301.
Science
Court Concept Abused
Report by Chris Peterson
In a recent "Science Court" cover story in OMNI
magazine, writer Ed Regis asked prominent scientists to decide
cases involving both scientific or technological and ethical
issues--the sorts of issues normally decided by social norms,
legislation, or a court of law. This mixing of issues violates
the most basic premise of the science court (SC) procedure,
developed by Arthur
Kantrowitz, which has as its ideal the separation of
scientific and technological questions from legal, ethical, and
emotional ones.
The SC goal is not to permit scientists to make pronouncements on
public policy issues, but rather just the opposite: to enable
society to extract from expert communities their best available
understanding of scientific and technological facts, burdened by
a minimum of personal opinion from the technical people involved.
This technical understanding could then be used by legislators,
judges, and other policymakers selected by society in the usual
ways. Proponents of the idea readily admit that perfect
separation of facts from values is not possible, but maintain
that we as a society could get a clearer understanding of
technical realities by means of the SC procedure than by means of
media wars, secret committees, and congressional hearings.
The OMNI article features "decisions" from
ten prominent scientists including physicist Stephen Hawking,
MIT's Seymour Papert, Edward Teller, and computer scientist
Joseph Weizenbaum. They were asked to make legal or ethical
pronouncements on surrogate motherhood, genetic engineering in
humans, alleged psychic powers, patenting genetically engineered
animals, and ownership of ancient human bones.
One scientist, the late Richard
Feynman, refused to participate on the excellent grounds that
scientists have no special ability to solve legal and ethical
issues: "Suppose I had one hundred percent access to the
facts and one hundred percent knowledge of the laws of nature.
None of this would tell me whether a surrogate mother should keep
her baby or whether designer animals ought to be patented."
The other participants presumably were either unfamiliar with the
original SC concept or were unable to resist the temptation to
mix their personal ethical views with their scientific
knowledge--a temptation the SC procedure is designed to
circumvent.
The SC is not a new proposal; it has been endorsed by various
presidential candidates in past elections. Originally seen as a
function within government, the idea has evolved into a procedure
which could be used in a decentralized way, for example at
universities.
As stated by Arthur Kantrowitz (now a professor at Dartmouth) in
his letter of correction to OMNI, "There have
been exercises at Berkeley and Dartmouth which have helped in
developing procedures. But the task is difficult partially
because some scientists prefer high priests' robes to labcoats.
Again some people prefer not having to stretch their minds enough
to deal with the moral and ethical problems posed by a
science-based technology which grows more and more powerful at an
explosive rate. Those who would control this force ... must get
the scientific facts from the scientific community. However, they
must form their own moral and ethical judgments."
The confusion about the role of the science court is partly due
to its name, which was given to Dr. Kantrowitz's idea by the
media. It implies a similarity to a traditional court of law,
which by its nature cannot confine itself to matters of technical
fact. The name gives the impression that the SC could make public
policy, just as today's courts of law effectively make public
policy by determining how laws are interpreted. Here at FI we
substitute the term "fact forum"; Dr. Kantrowitz now
uses the term "scientific adversary procedure."
Another problem the SC meme has faced is the difficulty of
arranging in-person meetings of busy technical people who, by
definition, are adversaries on some issue. FI believes that the
establishment of hypertext publishing systems will support online
fact forum procedures. Meanwhile, existing software such as
DocuForum is being investigated; readers with suggestions on this
should contact FI.
For more on the SC/fact forum idea, see an account of the
first three trial SC procedures in a university setting, to be
published by Roger Masters and Arthur Kantrowitz in the upcoming
book Technology and Politics (ed.
Michael Kraft and Norman Vig, Duke University, in press). A basic
explanation of the idea is available in Engines of Creation
(K. Eric Drexler, Doubleday, 1986).--Editor
[Note: More recent information is
available on the Web at "Twenty-Five Year
Retrospective on the Science Court"]
Atoms,
Bits, and Mechanisms
When faced with something as novel as nanotechnology, it makes
sense to look for familiar analogies. Previous publications have
compared nanomachines to conventional macromachines, but in
important ways nanomachines more closely resemble software
systems. Consider the properties of software and conventional
machines, then the parallels with assembler-built nanomachines.
Macromachines are made of parts which contain vast numbers of
atoms in ill-defined patterns. Having so many atoms, these parts
can be made in what amounts to a continuum of sizes and shapes,
formed by continuous, analog techniques--molding, cutting,
grinding, etching, and so forth. These parts are always
imprecise. Machines are made by fitting parts together; in a good
design, imprecisions won't add up to exceed overall tolerances.
In operation, parts typically change shape slowly--they wear out
and fail.
Software mechanisms differ radically. Their parts consist of
discrete bits in defined patterns--they do not form a continuum.
There is no need to make bits, as there is to make mechanical
parts. The fabrication of bit-patterns is a precise, digital
process; it is either entirely correct or clearly wrong, never
"just a little off." The position of one bit with
respect to another is as precise as the mathematical position of
"two" with respect to "three."
The digital mechanisms which underlie this precision are made of
imprecise devices, but these devices have distinct patterns of
interconnection and distinct "on" and "off"
states. Failures in the underlying devices can cause sporadic
errors in memory and logic, yet if the devices operate within
their design tolerances, errors (give or take an occasional
cosmic ray) will be completely absent. Digital precision emerges
from imperfect devices through a process like that of the
automatic alignment found in many computer graphics programs: a
device in any state that is nearly-right snaps into a neighboring
state that is entirely-right. Each entirely-right state follows
from a previous entirely-right state, with no buildup of small
errors in, say, the size or alignment of the bits.
Nanomechanisms do have obvious similarities to conventional
mechanisms. Unlike software, they will be made of parts having
size, shape, mass, strength, stiffness, and so forth. They will
often include gears, bearings, shafts, casings, motors, and other
familiar sorts of devices designed in accord with familar
principles of mechanical engineering. In most respects,
nanomechanical parts will resemble conventional parts, but made
with far, far fewer atoms. They will little resemble the
algorithms and data structures of software.
And yet their similarity to software and digital mechanisms will
be profound. As software consists of discrete patterns of bits,
so nanomechanisms will consist of discrete patterns of atoms.
Atoms, like bits, need not be made; they are both flawless and
available without need for manufacture. The parts of
nanomechanisms will not form a continuum of shapes, built by
inaccurate analog processes; they will instead be chosen from a
discrete set of atom-patterns, and (like bit patterns) these
patterns will be either entirely correct or clearly wrong. In
stacking part on part there will be no buildup of small errors,
as there is in conventional systems.
As in digital circuits and computer graphics programs, a
principle of automatic alignment comes into play. When an
assembler arm positions a reactive group against a workpiece,
forcing a reaction, imprecision of the arm's alignment won't
cause imprecision in the position of the added atoms. In making a
well-bonded object, molecular forces will snap the atoms either
into the proper position, or into a clearly wrong position. (As Marvin
Minsky remarks, quantum mechanics doesn't always make things
more uncertain--quantum states can be extraordinarily definite
and precise.) Assembly can with high reliability yield a perfect
result.
And again like software, nanomechanisms won't wear out. So long
as all the atoms in a mechanism are present, properly bonded, and
not in a distinct, excited state, the mechanism is perfect. If an
atom is missing or displaced (say, by radiation damage) the
mechanism isn't worn--it is broken.
In their shapes and functions, nanomechanisms will be much like
ordinary machines. But in their discreteness of structure and
associated perfection--to say nothing of their speed, accuracy,
and replicability--nanomechanisms will share some of the
fundamental virtues of software.
From Foresight Update 3, originally
published 30 April 1988.
Foresight thanks Dave Kilbridge for converting Update 3 to
html for this web page.
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