Computing with Molecules Source: New Scientist Radical departures from present computing design will
probably be needed to exploit molecular computing systems fully.
How fast and powerful can computers become? Will it be
possible someday to create artificial "brains" that have intellectual
capabilities comparable--or even superior--to those of human beings?
The answers to these questions depend to a very great extent on a
single factor: how small and dense we can make computer circuits.
Few if any researchers believe that our present
technology--semiconductor-based solid-state microelectronics--will
lead to circuitry dense and complex enough to give rise to true
cognitive abilities. And until recently, none of the technologies
proposed as successors to solid-state microelectronics had shown
enough promise to rise above the
pack. Within the past year, however, scientists have achieved
revolutionary advances that may very well radically change the future
of computing. And although the road from here to intelligent machines
is still rather long and might turn out to have unbridgeable gaps, the
fact that there is a potential path at all is something of a triumph.
The recent advances were in molecular-scale electronics,
a field emerging around the premise that it is possible to build
individual molecules that can perform functions identical or analogous
to those of the transistors,
diodes, conductors and other key components of today's microcircuits.
After a period of high hopes but few tangible results, several
developments over the past few years have raised expectations that
this technology may one day provide the building blocks for future
generations of ultrasmall, ultradense
electronic computer logic. In a remarkable series of demonstrations,
chemists, physicists and engineers have shown that individual
molecules can conduct and switch electric current and store
information.
Last July, in an achievement widely reported in the
popular press, researchers from Hewlett-Packard and the University of
California at Los Angeles announced that they had built an electronic
switch consisting of a layer of several million molecules of an
organic substance called rotaxane. By linking a number of switches,
the researchers produced a rudimentary version of an AND gate, a
device that performs a basic logic operation. With well over a million
molecules apiece, the switches are far larger than would be desirable.
And they could be switched only one time before becoming inoperable.
Nevertheless, their assembly into a logic gate was of fundamental
significance.
Within months of that announcement, our groups at Yale
and Rice universities published results on a different class of
molecules that acted as a reversible switch. And one month later we
described a molecule we had created that could change its electrical
conductivity by storing electrons on demand, acting as a memory
device.
To produce our switch, we inserted regions into the
molecules that trapped electrons, but only when the molecules were
subjected to certain voltages. Thus, the degree to which the molecules
resisted a flow of electrons depended on the voltage applied to them.
In fact, by varying the voltage, we
could repeatedly change the molecules at will from a conducting to a
nonconducting state--which is the basic requirement for an electrical
switch. The tiny device actually consisted of a layer of about 1,000
molecules of nitroamine benzenethiol sandwiched between metal
contacts.
After creating the switch, we realized that if we could
redesign the molecule so that it could retain electrons rather than
trapping them briefly, we would have something that could work as a
memory element. We went to work on the trapping region of the
molecule, modifying it so that its conductivity could be changed
repeatedly. The resulting "electron sucker" could retain electrons for
nearly 10 minutes--compared with a
few milliseconds for conventional silicon-based dynamic random-access
memory.
Although the advances were encouraging, the challenges
remaining are enormous. Creating individual devices is an essential
first step. But before we can build complete, useful circuits we must
find a way to secure many millions, if not billions, of molecular
devices of various types against some kind of immobile surface and to
link them in any manner and into
whatever patterns our circuit diagrams dictate. The technology is
still too young to say for sure whether this monumental challenge will
ever be surmounted.
The End of the Road Map
Given the magnitude of the challenges ahead, why did
researchers and even the mainstream media pay so much attention to the
recent advances? The answer has to do with industrial society's
dependence on microelectronics--and the limits of the form of the
technology we have today.
That form--solid-state and silicon-based--follows one of
the most famous axioms in technology: Moore's Law. It relates that the
number of transistors that can be fabricated on a silicon integrated
circuit--and therefore the computing speed of such a circuit--is
doubling every 18 to 24 months. After
following this remarkable curve for four decades, solid-state
microelectronics has advanced to the point at which engineers can now
put on a sliver of silicon of just a few square centimeters some 100
million transistors, with key features measuring 0.18 micron.
These transistors are still far larger than
molecular-scale devices. To put the size differential in perspective,
if the conventional transistor were scaled up so that it occupied the
printed page you are reading, a molecular
device would be the period at the end of this sentence. Even in a
dozen years, when industry projections suggest that silicon
transistors will have shrunk to about 120 nanometers in length, they
will still be more than 60,000 times larger in area than molecular
electronic devices.
Moreover, no one expects conventional silicon-based
microelectronics to continue following Moore's Law forever. At some
point, chip-fabrication specialists will find it economically
infeasible to continue scaling down microelectronics. As they pack
more transistors onto a chip, phenomena such as stray signals on the
chip, the need to dissipate the heat from so many closely packed
devices, and the difficulty of creating the devices in the first place
will halt or severely slow progress.
Indeed, various nagging (though not yet fundamental)
problems in the fabrication of efficient smaller silicon transistors
and their interconnections are becoming increasingly bothersome. Many
experts expect these challenges to intensify dramatically as the
transistors approach the
0.1-micron level. Because of these and other difficulties, the
exponential increase in transistor densities and processing rates of
integrated circuits is being sustained only by a similar exponential
rise in the financial outlays necessary to build the facilities that
produce these chips. Eventually the drive to downscale will run
headlong into these extreme facility costs, and the market will reach
equilibrium. Many experts
project that this will happen around or before 2015, when a
fabrication facility is projected to cost nearly $200 billion. When
that happens, the long period of breathtaking advances in the
processing power of computer chips will have run its course. Further
increases in the power of the chips will be prohibitively costly.
Unfortunately, this impasse will almost certainly occur
long before computer chips have reached the power to fulfill some of
the most sought-after goals in computer science, such as the creation
of extremely sophisticated electronic "brains" that will enable robots
to perform on a par with humans in intellectual and cognitive tasks.
Billions and Billions
The extraordinarily small size of molecular devices
brings advantages beyond the simple ability to pack more of them into
a small area. To grasp these important benefits requires an
understanding of how the devices work--which in turn demands some
knowledge of how electrons behave when confined
to regions as small as atoms and molecules.
Free electrons can take on energy levels from a
continuous range of possibilities. But in atoms or molecules,
electrons have energy levels that are quantized: they can only be any
one of a number of discrete values, like rungs on a ladder. This
series of discrete energy values is a consequence of
quantum theory and is true for any system in which the electrons are
confined to an infinitesimal space. In molecules, electrons arrange
themselves as bonds among atoms that resemble dispersed "clouds,"
called orbitals. The shape of the orbital is determined by the type
and geometry of the constituent atoms. Each orbital is a single,
discrete energy level for the electrons.
Even the smallest conventional microtransistors in an
integrated circuit are still far too large to quantize the electrons
within them. In these devices the movement of electrons is governed by
physical characteristics--known as
band structures--of their constituent silicon atoms. What that means
is that the electrons are moving in the material within a band of
allowable energy levels that is quite large relative to the energy
levels permitted in a single atom or molecule. This large range of
allowable energy levels permits electrons to gain enough energy to
leak from one device to the next. And when these conventional devices
approach the scale of a few hundred
nanometers, it becomes extremely difficult to prevent the minute
electric currents that represent information from leaking from one
device to an adjacent one. In effect, the transistors leak the
electrons that represent information, making it difficult for them to
stay in the "off" state.
Building from the Bottom Up
Besides enabling molecular devices to contain their
electrons more securely, quantum mechanical phenomena can also be
exploited in specially designed molecules to perform other functions.
For example, to construct a "wire" we need an elongated molecule
through which electrons can flow easily
from one end to the other. Electrons in any quantized structure such
as a molecule tend to move from higher-to lower-energy levels, so in
order to channel electrons we need a molecule that has an empty,
low-energy orbital that is dispersed throughout the molecule from one
end to the other. A typical empty, low-energy electron orbital is
known as a pi orbital. And the configuration in which electron clouds
overlap from one molecular
component to the next is called conjugated, so our molecular wire is
known as a "pi-conjugated system."
An active device such as a transistor, however, has to
do more than merely allow electrons to flow--it has to somehow control
that flow. Thus, the task of the molecular device engineer is to
exploit the quantum world's discrete energy levels--specifically, by
designing molecules whose orbital
characteristics achieve the desired kind of electronic control. For
example, with the right overlap of orbitals in the molecule, electrons
flow. But when the overlap is disturbed--because the molecule has been
twisted or its geometry has been otherwise affected--the flow is
blocked. In other words, the key to control on the molecular scale is
manipulating the number of
electrons that are allowed to flow at low orbital energy by perturbing
the orbital overlap through the molecule.
Already the standard methods of chemical synthesis allow
researchers to design and produce molecules with specific atoms,
geometries and orbital arrangements. Moreover, enormous quantities of
these molecules are created at the same time, all of them absolutely
identical and flawless. Such uniformity is extremely difficult and
expensive to achieve in other batch-fabrication processes, such as the
lithography-based process
used to produce the millions of transistors on an integrated circuit.
The methods used to produce molecular devices are the
same as those of the pharmaceutical industry. Chemists start with a
compound and then gradually transform it by adding prescribed reagents
whose molecules are known to bond to others at specific sites. The
procedure may take many steps, but
gradually the pieces come together to form a new potential molecular
device with a desired orbital structure. After the molecules are made,
we use analytical technologies such as infrared spectroscopy, nuclear
magnetic resonance and mass spectrometry to determine or confirm the
structure of the molecules. The various technologies contribute
different pieces of information about the molecule, including its
molecular weight and the connection point or angle of a certain
fragment. By combining the information, we determine the structure
after each step as the new molecule is synthesized.
One of our simplest active devices was a molecule based
on a string of three benzene rings, in which the orbitals overlapped
(were conjugated) throughout. We made the connections between the
benzene rings structurally weak, so that slight twists or kinks
weakened or strengthened the conjugation of the orbitals. All we
needed was a way to control this twisting and we would have a
molecular device in which we could control current flow--a switch, in
other words.
To the center benzene ring in the molecule, we added NO2
and NH2 groups, projecting outward from the string on opposite sides
of the center ring. This asymmetrical configuration left the molecule
with a strongly perturbed
electron cloud. That asymmetric, perturbed cloud in turn made the
molecule very susceptible to distortion by an electric field: applying
an electric field to the molecule twisted it. We now had an active
device: every time we applied a voltage to the molecule, an electric
field was set up that twisted the molecule and blocked current flow.
With the voltage removed, the molecule sprang back to its original
shape, and the current flowed
again. In follow-up experiments, we found that for our infinitesimal
device the abruptness of the switching from one state to the other was
superior to that of any comparable solid-state device.
Of course, a lot of advanced technology and years of
research were necessary before we could even test one of these
devices. The basic challenge is reaching into an unfathomably
Lilliputian domain in order to contact and interact with a single
molecule and bring information about the behavior of that molecule
into our macroscopic world.
The task was all but impossible before the invention, in
the 1980s, of the scanning tunneling microscope (STM) at IBM's
research laboratories in Zurich. The STM gives scientists a window on
the atomic world, letting them visualize and manipulate single atoms
or molecules. With an atomically
sharp tip of metal held precisely over a surface, the topography of
the surface is sensed by the minute current of tunneling electrons
that flows between the surface and the tip. Rastering the tip back and
forth creates a picture of the hills and valleys on the surface.
Although scanning tunneling microscopy is crucial for
testing and constructing individual devices, any useful molecular
circuit will consist of vast numbers of devices, orderly arranged and
securely affixed to a solid structure to keep them from interacting
randomly with one another. Progress
toward solving this huge challenge has emerged from studies of
self-assembly, a phenomenon in which atoms, molecules or groups of
molecules arrange themselves spontaneously into regular patterns and
even relatively complex systems without intervention from outside.
Molecular Glue
Once the assembly process has been set in motion, it
proceeds on its own to some desired end [see "Self-Assembling
Materials," by George M. Whitesides; Scientific American, September
1995]. In our research we use self-assembly to attach extremely large
numbers of molecules to a surface, typically
a metal one [see illustration on self-assembly]. When attached, the
molecules, which are often elongated in shape, protrude up from the
surface, like a vast forest with identical trees spaced out in a
perfect array.
The Basics
The inexorable drive to produce smaller devices may
leave technologists no choice but to migrate to a new form of
electronics in which specially designed individual molecules replace
the transistors of today's circuits. That forced migration could come
about within the next decade, some researchers believe.
The bare requirements for a general-purpose computer are
a switching device (like a transistor), memory and a way of connecting
arbitrarily large numbers of the devices and memory elements. So far
scientists have managed to produce single-molecule switches and memory
elements. The switch, however, had only two terminals. Realistically,
to construct complex logic circuits requires a device with more than
two terminals, in which, for example, current flow between two is
controlled by a third (that is the way transistors work).
Even more imposing, scientists lack a method of
connecting huge numbers of the devices. Although no potential
solutions to this problem are apparent yet, researchers suspect that
radically new architectures and conventions will be needed to exploit
molecular devices fully.
Researchers have studied a variety of self-assembly
systems. Our work often requires us to attach molecular devices to a
metal (usually gold) surface. So we frequently work with a molecular
fragment that we attach to one or both ends of our device and that has
a high affinity for gold atoms. The
specific fragment we commonly use, called a "sticky" end group for
obvious reasons, is based on an atom of sulfur and is known in
chemical terminology as thiol.
To initiate the self-assembly, we need only dip a gold
surface into a beaker. In solution in this container are our molecular
devices, each with thiol end groups on both ends. Spontaneously and in
unimaginably large numbers, the devices attach themselves to the gold
surface.
Handy though it is, self-assembly alone will not suffice
to produce useful molecular-computing systems, at least not initially.
For some time, we will have to combine self-assembly with fabrication
methods, such as photolithography, borrowed from conventional
semiconductor manufacturing. In photolithography, light or some other
form of electromagnetic
radiation is projected through a stencil-like mask to create patterns
of metal and semiconductor on the surface of a semiconducting wafer.
In our research we use photolithography to generate layers of metal
interconnections and also holes in deposited insulating material. In
the holes, we create the electrical contacts and selected spots where
molecules are constrained to self-assemble. Thus, the final system
consists of regions of self-assembled molecules attached by a mazelike
network of metal interconnections.
The first successful demonstration of self-assembly in
molecular electronics occurred just four years ago, in 1996, when Paul
S. Weiss's group at Pennsylvania State University tested
self-assembled molecules. One of us (Tour), then at the University of
South Carolina, synthesized the devices. Weiss and his colleagues
found that by mixing a small amount of a solution of molecules that
were designed to have conducting properties with another containing a
known inert insulating molecule, they could get a self-assembled layer
in which conductive molecules were very sparsely interspersed among
nonconductive ones. By positioning the tip of an STM directly over one
of the isolated conducting molecules, they could
qualitatively measure the conductivity. As expected, it was
significantly greater than that of the surrounding molecules. Similar
results were also obtained by a group at Purdue University, which
tagged the top of the conductive molecules with minute gold particles.
At the same time at Yale, one of us (Reed) performed the
first quantitative electrical measurements of a single molecule, which
was also fabricated by self-assembly. Specifically, Reed and his group
measured how much current could flow across a single molecule. The
heart of the experimental setup was an STM modified to enable it to
position two tips opposite each other with sufficient precision and
mechanical stability to contain a single molecule in between [see
illustration]. A very simple molecule was used to convey mobile
electrons: a single benzene ring with sticky thiol end groups
on both ends to contact the metal leads of the STM tips. It turned out
that the resistance of the molecule was in the range of tens of
millions of ohms.
The Yale researchers also found that the molecule could
sustain a current of about 0.2 microampere at five volts--which meant
that the molecule could channel through itself roughly a million
million (1012) electrons per second. The number is impressive--all the
more so in light of the fact that
the electrons can pass through the molecule only in single file (one
at a time). The magnitude of the current was far larger than would be
expected from simple calculations of the power dissipated in a
molecule, leading to the conclusion that the electrons traveled
through the molecule without generating heat by interacting or
colliding.
These initial observations of conduction in molecules
were followed quickly by demonstrations of basic devices. The simplest
electronic device is a diode, which can be thought of as a one-way
valve for electrons. In 1997, only a year after the first measurements
of conduction in molecules,
two separate research groups built diodes. At the University of
Alabama, Robert M. Metzger's group synthesized a molecule that had an
internal energetic lineup of orbitals, which varied depending on the
polarity of the voltage applied to it. The lineup of orbitals was
analogous to the rungs on a ladder. With the voltage applied in one
direction, the lineup corresponded to a ladder propped against a
house. In this orientation, it takes
considerable effort to climb the ladder. With the opposite voltage
polarity, the orbital lineup was analogous to the rungs of a ladder
lying flat on the ground, where it can be traversed with little
effort.
In the other group at Yale, Chong-Wu Zhou took a
slightly different tack. With this molecular diode, the differences in
the lineup of the energy levels occurred externally to the molecule,
where it contacted the metal. This scheme also worked well and helped
to set the stage for the design of more useful and interesting
molecular devices and circuits.
Connecting from the Top Down
As they began constructing such devices, the Yale group
adapted a structure first made by Kristin Ralls and Robert A. Buhrman
of Cornell University. The structure contained an extremely minute
hole, called a nanopore, in which an "active region" was created by
self-assembling a relatively small number of molecular devices in a
single layer, or monolayer. In a hole just 30 nanometers wide,
approximately 1,000 of the molecular devices were allowed to
self-assemble. Evaporating a metal contact onto the top of the
self-assembled monolayer ("SAM") completed the device.
After using this configuration to produce and test
molecular diodes, the Yale group quickly moved on to more complex
devices, namely, switches. A controllable switch of some kind is a
minimum requirement for a general-purpose computer. Even more
desirable is a switch that can amplify a current, besides merely
turning it on and off. Such amplification is
necessary to connect vast numbers of the switches, as is required to
build complex logic circuits. The silicon transistor fulfills both
those requirements, which is why it is one of the great success
stories of the 20th century.
The molecular equivalent of a transistor that can both
switch and amplify current is yet to be discovered. But researchers
have taken the first steps along the path by constructing switches,
such as the twisting switch described earlier. In fact, Jia Chen, a
graduate student in Reed's Yale
group, observed impressive switching characteristics, such as an
on/off ratio greater than 1,000, as measured by the current flow in
the two different states. For comparison, the analogous device in the
solid-state world, called a resonant tunneling diode, has an on/off
ratio of around 100.
Similar behavior was observed in the U.C.L.A./HP
experiments. In their demonstration, they showed that the conductivity
of a molecular layer of rotaxanes, molecules that resemble a core with
a surrounding barbell, could be predictably interrupted when a high
voltage was applied to a junction containing the molecules. At this
voltage, the molecules reacted and changed configuration, altering the
lineup of orbitals and interrupting the flow of current through the
molecule. Combining a series of these junctions, they built a device
that performed a simple logic function.
Perhaps most encouragingly, molecular devices have
already proved themselves as memory elements. Besides active,
transistorlike devices, memory is the other main requirement for a
useful, general-purpose computer. Recall our twisting switch. We
altered the internal electrically active unit (the lopsided center
benzene ring with opposing NO2 and NH2 groups) by keeping
just the "electron-sucking" nitro group, NO2. The change made the
molecular orbitals susceptible to becoming modified--either spread out
or localized depending on the charge state of the internal group.
Absence or presence of charge in the internal node would modify the
conduction of electrons through the molecule. By storing charge on the
nitro group, we blocked the
conduction, which represents a binary "0." Conversely, with no charge
stored on the group, the conduction was high, representing a binary
"1." Significantly, the molecular memory cell retained (or
"remembered," if you will) the stored bit for nearly 10 minutes--an
astounding amount of time in comparison with an ordinary silicon
dynamic random-access memory (DRAM)
element, which can hang on to a bit for only a few milliseconds
(silicon DRAMs must be frequently refreshed by an external circuit to
retain their data). The construction of the memory element, which
involved a relatively straightforward modification to the twisting
switch, also demonstrated the ease and flexibility in which
molecular-scale devices can be redesigned.
Given the enormous potential advantages of molecular
devices, why don't we scrap silicon research and proceed
wholeheartedly to molecular-based systems? Because despite the recent
auspicious advances, a number of significant obstacles, some
fundamental, still stand in the way of fabulously complex and powerful
circuits.
Needed: The Next Transistor
Foremost among them is the challenge of making a
molecular device that operates analogously to a transistor. A
transistor has three terminals, one of which controls the current flow
between the other two. Effective though it was, our twisting switch
had only two terminals, with the current flow
controlled by an electrical field. In a field-effect transistor, the
type in an integrated circuit, the current is also controlled by an
electrical field. But the field is set up when a voltage is applied to
the third terminal.
A three-terminal molecular device will make possible the
chemical synthesis of tremendously efficient and complex circuits.
Even before then, combinations of molecular systems with conventional
electronics will probably be used in places where the advantages of
self-assembly are natural. But interfacing between the molecular and
microelectronic worlds
will present its own challenges. Computer chips today have two levels
of size scale. From the macroscopic level of the chip we can see and
hold in our hand, there is a factor of 1,000 in size reduction to get
to the gross wiring level, encompassing the largest connections on the
chip, which are smaller than a human hair. Then another
factor-of-1,000 reduction is necessary to get to the level of the
smallest connections and components of the transistors. If molecular
devices are to be added to a chip, they
will represent yet another factor-of-1,000 reduction in scale down
from the smallest microelectronic device components.
Thermal challenges are also staggering, especially if
engineers wind up with no alternatives to using molecular devices in
modes and configurations similar to those used now with transistors in
conventional chips. At present, a state-of-the-art microprocessor with
10 million transistors and a clock cycle of half a gigahertz (half a
billion cycles per second)
emits almost 100 watts--greater in radiant heat than a range-top
cooking surface in the home. Such a unit is close to the thermal
limitation of semiconductor technology. Knowing the minimum amount of
heat that a single molecular device emits would help put a limit on
the number of devices we could put on a chip or substrate of some
kind.
This fundamental limit of a molecule, operating at room
temperature and at today's speeds, is about 50 picowatts (50
millionths of a millionth of a watt). That figure suggests an upper
limit to the number of molecular devices we can closely aggregate: it
is roughly 100,000 times more that what we can now do with silicon
microtransistors on a chip. Although that may
seem like a vast improvement, it is still far below the density that
would be possible if we did not have to worry about heat.
For these calculations, we followed the convention in
silicon microelectronics that every device is addressable--or, put
another way, that any device can be picked out from among the
countless millions through the interconnections, like a house with a
unique street address. This kind of addressing (which is called random
access) would be required, for example,
to retrieve the contents of a particular memory location.
Right now no one knows how to create such an
interconnect structure on the molecular level. Straightforward
extensions of the present techniques we employ to fabricate complex
microelectronics are not practical for molecular-scale electronics,
because the lithography needed for creating the
interconnections to single molecules is far beyond the capability of
known technologies. Is the ability to address every device, the common
architecture we use today, necessary or efficient at molecular-scale
densities? What will large-scale circuits of this technology look
like? Can we use nanotubes, single-walled structures of carbon with
diameters of one or two nanometers and lengths of less than a micron,
as the next
generation of interconnects between molecular-scale devices?
Decades from now, radical departures from present
computing design will probably be needed to exploit molecular
computing systems fully if we are to extend electronics significantly
beyond Moore's Law. We have only very limited ideas about what these
departures might be. The ability to
construct complex molecular devices, with new paradigms and lists of
rules about connecting the various devices, will open up an entirely
different way to think about computer design.
Although such departures are fraught with problems, we
have no alternative but to solve them if electronics is to continue
advancing at something like its current pace well into the next
century. And difficult though the
challenges may be, the rewards for those who solve the problems could
be staggering. By pushing Moore's Law past the limits of the
tremendously powerful technology we already have, these researchers
will take electronics into vast, uncharted terrain. If we can get to
that region, we will almost certainly find some wondrous things--maybe
even the circuitry that will give rise to our intellectual successor.
Further Information:
CONDUCTANCE OF A MOLECULAR JUNCTION. M. A. Reed, C.
Zhou, C. J. Muller, T. P. Burgin and J. M. Tour in Science, Vol. 278,
pages 252-254; October 10, 1997.
A DEFECT-TOLERANT COMPUTER ARCHITECTURE: OPPORTUNITIES
FOR NANOTECHNOLOGY. J. R. Heath, P. J. Kuekes, G. S. Snider and R. S.
Williams in Science, Vol. 280, pages 1716-1721; June 12, 1998.
MOLECULAR ELECTRONICS: SCIENCE AND TECHNOLOGY. Edited by
A. Aviram and M. Ratner. Annals of the New York Academy of Sciences,
Vol. 852; 1998.
The Authors
MARK A. REED and JAMES M. TOUR began collaborating on
molecular electronics research in 1990. Reed is chairman of the
department of electrical engineering and the Harold Hodgkinson
Professor of Engineering and Applied Science at Yale University. His
research interests include nanotechnology and the fundamental limits
of electronic conduction. A former research scientist at Texas
Instruments, he recently founded with Tour the Molecular Electronics
Corporation in Chicago with the aim of making molecular electronics
commercially viable. He is author of over 100 publications and holds
17 patents on quantum effect, heterojunction and molecular devices.
Tour is a synthetic organic chemist who has been designing and
synthesizing
molecules for molecular electronics for 10 years. He is with the
department of chemistry and the Center for Nanoscale Science and
Technology at Rice University, where he pursues chemical aspects of
molecular electronics. Previously, he was at the University of South
Carolina, where he spent 11 years on the faculty of the department of
chemistry.
by Mark A. Reed and James M. Tour
http://www.sciam.com/2000/0600issue/0600reed.html