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MOLETRONICS- an invisible technology
ABSTRACT
Semiconductor integration beyond Ultra Large Scale Integration (ULSI), through
conventional electronic technology facing some problems with fundamental physical
limitations. Beyond ULSI, a new technology may become competitive to semiconductor
technology.This new technology is known as Molecular Electronics .Molecular based
electronics can overcome the fundamental physical and economic issues limiting Si
technology. Here, molecules will be used in place of semiconductor, creating electronic
circuit small that their size will be measured in atoms. By using molecular scale
technology, we can realize molecular AND gates, OR gates, XOR gates etc.
The dramatic reduction in size, and the sheer enormity of numbers in manufacture, are the
principle
benefits
promised
by
the
field
of
molecular
electronics.
INTRODUCTION
Molecular electronics, one of the major fields of current efforts in nanoscience,
involves the exploration of the electronic level structure, response and transport,
together with the development of electronic devices and applications that depend on
the properties of matter at the molecular scale. This includes single molecules,
molecular arrays and molecular networks connected to other electronic components.
Its major application areas include sensors, displays, smart materials,molecular
motors, logic and memory devices, molecular scale transistors and energy
transduction devices. Often molecular electronics is envisioned as the next step in
device miniaturization. The importance of molecules in device applications stems not
only from their electronic properties, but also from their ability to bind to one another,
recognize each other, assemble into larger structures, and exhibit dynamical
stereochemistry.
Molecular Electronics overview
Molecular electronics (sometimes called moletronics) is a branch of applied physics
which aims at using molecules as passive (e.g. resistive wires) or active (e.g.
transistors)electronic
components.
The concept of molecular electronics has aroused much excitement both in science
fiction and among scientists due to the prospect of size reduction in electronics offered
by such minute components. It is an enticing alternative to extend Moore's Law
beyond the foreseen limits of small-scale conventional silicon integrated circuits. As a
result,
molecular electronics is
currently
a
very
active
research
field.
Among the important issues is the determination of the resistance of a single molecule
(both theoretical and experimental). Another problem faced by this field is the difficulty
to perform direct characterization since imaging at the molecular scale is often
impossible
in
many
experimental
devices.
History
Study of charge transfer in molecules was advanced in the 1940s by Robert Mulliken
and Albert Szent-Gyorgi in discussion of so-called "donor-acceptor" systems and
developed the study of chargetransfer and energy transfer in molecules. Likewise, a
1974 paper from Mark Ratner and Avi Aviram 1 illustrated a theoretical molecular
rectifier. Later, Aviram detailed a single-molecule field-effect transistor in 1988. Further
concepts were proposed by Forrest Carter of the Naval Research Laboratory,
including
Apart
from
single-molecule
the
Aviram
and
Ratner
logic
proposal,
gates.
molecular electronics received
an initial boost from the experimental discovery of conducting polymers in the midseventies. Before this date, organic molecules (which form crystals or polymers) were
considered insulating or at best weakly conducting semi-conductors. In 1974,
McGinness, Corry, and Proctor reported the first molecular electronic device in the
journal Science. As its active element, this voltage-controlled switch used melanin, an
oxidized mixed polymer of polyacetylene, polypyrrole, and polyaniline. The "ON" state
of this switch exhibited extremely high conductivity. This device is now in the
Smithsonian's collection of historic electronic devices. As Hush notes, their material
also showed negative differential resistance, "a hallmark of modern advances in
molecular electronics". Melanin is also the first example of a "self-doped" organic
semiconductor, though McGinness et al also looked at dopants such as diethyamine.
A few years later, in 1977, Shirakawa, Heeger and MacDiarmid rediscovered the
potential high conductivity of oxidized ("doped") polyacetylene, producing a passive
highly-conductive form of polyacetylene. For this discovery and its subsequent
development, they received the 2000 Nobel prize in physics. Subsequentely, chemists
greatly improved the conductance of conjugated polymers. These findings opened the
door to plastic electronics and optoelectronics, which are beginning to find extensive
commercial application.
About
Molecular Electronics
The guiding principle of this research is that biological systems can provide useful
paradigms for developing electronic and computational devices at the molecular level.
For example, natural photosynthetic reaction centers are photovoltaic devices of
molecular dimensions, and the principles dictating the operation of reaction centers
may be useful in the design of synthetic optoelectronic switches. In this project, several
classes of molecular photovoltaic species are being synthesized and studied. These
include porphyrin-fullerene dyads, carotenoid-fullerene dyads, a carotenoid-porphyrinfullerene triad, carotene-porphyrin-imide triads, and molecular dyads and triads
containing
two
porphyrin
moieties.
The approach involves the design and synthesis of dyads, triads and other super
molecular species using the techniques of organic chemistry. The newly-prepared
molecules are then studied by a variety of physical methods, including time-resolved
laser spectroscopy, NMR spectroscopy, and cyclic voltammetry in order to determine
how and how well they functioned as molecular electronic elements. The information
gained can then be used to design new generations of these molecules.
Once functional molecular photovoltaics, logic gates, or other elements have been
prepared, ways must be developed for interfacing these with electronic circuits.
Possibilities are being investigated in a collaborative project with Professor Michael
Kozicki,
in
the
Department
of
Electrical
Engineering.
The triad shown above is an example of a molecule that may be useful in molecular
electronic applications. Buckminsterfullerene (C60) and its relatives have generated
considerable excitement in recent years due to their status as new and unusual forms
of carbon which are completely unrelated to the many carbon compounds synthesized
by living organisms. In spite of their non-biological origin, it turns out that fullerenes are
nearly ideal as components of molecules that mimic natural photosynthetic energy and
electron transfer.
This molecular "triad" consists of a synthetic porphyrin (P) covalently linked to both a
fullerene (C60) and a carotenoid polyene © (J. Am. Chem. Soc. 1997, 119, 1400-
1405). When the porphyrin absorbs light, it donates an electron to the fullerene,
yielding C-P¢ -C60¢ . The carotenoid then transfers an electron to the porphyrin to
give a final C¢ -P-C60¢ charge-separated state. This state has a relatively long
lifetime, and stores a considerable fraction of the light energy as electrochemical
potential energy. This conversion of light energy to electrochemical potential is
analogous to the way plants carry out solar energy harvesting during photosynthesis.
The charge-separated state is formed even at 8 degrees Kelvin in a frozen
environment, and ultimately decays by charge recombination to yield the carotenoid
triplet excited state, rather than the original ground-state molecule. The generation in
the triad of a long-lived charge separated state by photo induced electron transfer, the
low-temperature electron transfer behavior, and the formation of a triplet state by
charge recombination are phenomena heretofore observed mostly in photosynthetic
reaction
centers.
The triads are molecular-scale photovoltaic cells. Their nanometer size and their ability
to generate an electrical response to light may help point the way to the development
of molecular-scale optoelectronic devices for communications, data processing, and
sensor applications. In fact, the triad shown above functions as a molecular-scale AND
logic gate. Two inputs (light and a weak magnetic field) are required to switch on the
output
of
the
gate,
which
may
be
detected
optically
or
electrically.
("Magnetic Switching of Charge Separation Lifetimes in Artificial Photosynthetic
Reaction Centers," D.Kuciaukas, P. a.Liddell, A.L.Moore, T.A.Moore and D.Gust,
J.Am.Chem.
Soc.,
Molecular
120,
10880-10886
Electronics
(1998).
Technology
The field of molecular electronics seeks to use individual molecules to perform
functions in electronic circuitry now performed by semiconductor devices. Individual
molecules are hundreds of times smaller than the smallest features conceivably
attainable by semiconductor technology. Because it is the area taken up by each
electronic element that matters, electronic devices constructed from molecules will be
hundreds of times smaller than their semiconductor-based counterparts. Moreover,
individual molecules are easily made exactly the same by the billions and trillions. The
dramatic reduction in size, and the sheer enormity of numbers in manufacture, is the
principle
benefits
offered
by
the
field
of
molecular
electronics.
At the heart of the semiconductor industry is the semiconductor switch. Because
semiconductor switches can be manufactured at very small scales and in combination
can be made to perform all desired computational functions, the semiconductor switch
has become the fundamental device in all of modern electronics. California Molecular
Electronics Corporation's Chiropticene® Switch is a switchable device that goes
beyond the semiconductor switch in size reduction. This switch is a single molecule
that
exhibits
classical
switching
properties.
The material listed herein provides insight into important technology areas of molecular
electronics. The documents are a "collection of works" on various topics in the field of
molecular electronics assembled by California Molecular Electronics Corporation
(CALMEC®) for the purposes of informing the non-scientific community on the
exciting technology of molecular electronics. At present, the topics include an
introduction to CALMEC's Chiropticene Molecular Switch Design, the principles behind
the Chiropticene Switch technology, its molecular engineering, and the patents that
protect
the
Chiropticene
Why
Switch
technology.
molecular
electronics
Essentially all electronic processes in nature, from photosynthesis to signal
transduction, occur in molecular structures. For electronics applications, molecular
structures
have
four
major
advantages:
¢ Size. The size scale of molecules is between 1 and100 nm, a scale that permits
functional nanostructures with accompanying advantages in cost, efficiency, and
power
dissipation
¢ Assembly and recognition. One can exploit specific intermolecular interactions to
form structures by nanoscale self-assembly. Molecular recognition can be used to
modify electronic behavior, providing both switching and sensing capabilities on the
single-molecule
scale.
¢ Dynamical stereochemistry. Many molecules have multiple distinct stable
geometric structures or isomers (an examples the relaxant molecule in figure 3d, in
which a rectangular slider has two stable binding sites along a linear track). Such
geometric isomers can have distinct optical and electronic properties. For example, the
retinal molecule switches between two stable structures, a process that transduces
light
into
a
chemo
electrical
pulse
and
allows
vision.
¢ Synthetic tailor ability. By choice of composition and geometry, one can extensively
vary a moleculeâ„¢s transport, binding, optical, and structural properties. The tools of
molecular
Transcending
synthesis
Mooreâ„¢s
are
Law
highly
with
Molecular
developed.
Electronics
The future of Mooreâ„¢s Law is not CMOS transistors on silicon. Within 25 years, they
will
be
as
obsolete
as
the
vacuum
tube.
While this will be a massive disruption to the semiconductor industry, a larger set of
industries depends on continued exponential cost declines in computational power and
storage density. Mooreâ„¢s Law drives electronics, communications and computers
and has become a primary driver in drug discovery and bioinformatics, medical
imaging and diagnostics. Over time, the lab sciences become information sciences,
and then the speed of iterative simulations accelerates the pace of progress.
There are several reasons why molecular electronics is the next paradigm for
Mooreâ„¢s
Law:
¢ Size: Molecular electronics has the potential to dramatically extend the
miniaturization that has driven the density and speed advantages of the integrated
circuit (IC) phase of Mooreâ„¢s Law. For a memorable sense of the massive difference
in scale, consider a single drop of water. There are more molecules in a single drop of
water than all transistors ever built. Think of the transistors in every memory chip and
every processor ever built, worldwide. Sure, water molecules are small, but an
important part of the comparison depends on the 3D volume of a drop. Every IC, in
contrast, is a thin veneer of computation on a thick and inert substrate.
¢ Power: One of the reasons that transistors are not stacked into 3D volumes today
is that the silicon would melt. Power per calculation will dominate clock speed as the
metric of merit for the future of computation. The inefficiency of the modern transistor
is staggering. The human brain is ~100 million times more power efficient than our
modern microprocessors. Sure the brain is slow (under a kHz) but it is massively
parallel (with 100 trillion synapses between 60 billion neurons), and interconnected in a
3D volume. Stan Williams, the director of HPâ„¢s quantum science research labs,
concludes: it should be physically possible to do the work of all the computers on Earth
today
using
a
single
watt
of
power.
¢ Manufacturing Cost: Many of the molecular electronics designs use simple spin
coating or molecular self-assembly of organic compounds. The process complexity is
embodied in the inexpensive synthesized molecular structures, and so they can
literally be splashed on to a prepared silicon wafer. The complexity is not in the
deposition
or
the
manufacturing
process
or
the
systems
engineering.
Biology does not tend to assemble complexity at 1000 degrees in a high vacuum. It
tends to be room temperature or body temperature. In a manufacturing domain, this
opens the possibility of cheap plastic substrates instead of expensive silicon ingots.
¢ Elegance: In addition to these advantages, some of the molecular electronics
approaches offer elegant solutions to non-volatile and inherently digital storage. We go
through unnatural acts with CMOS silicon to get an inherently analog and leaky
medium to approximate a digital and non-volatile abstraction that we depend on for our
design methodology. Many of the molecular electronic approaches are inherently
digital and immune to soft errors, and some are inherently non-volatile.
The
advantages
Mechanisms
render
of
molecules
ideal
molecular
for
electronics
applications
charge
transport
The synthesis and characterization of molecules are endeavors typically conducted in
solution. Decades of research have given chemistâ„¢s intuitive models that serve as a
guide for using synthetic control to design physical properties into a molecule. A key
challenge in molecular electronics is to translate that solution-phase intuition into solidstate device setting. Certain molecular structures have emerged as models for relating
intermolecular electron transfer rates in solution to solid-state molecular junction
conductance.
A picture of electron transport through molecular devices is emerging, and it
couldnâ„¢t be more different from what is observed for more traditional conductors.
Disregard, for the moment, the details of the electrical contact. In a semiconductor or
metal wire, charge transport isohmic: For a given wire diameter, longer wires have
proportionately higher resistance. Such a picture is usually wrong for molecules
because
of
the
localized
nature
of
most
molecular
electronic
states.
Consider the energy diagrams of figure 3, in which four types of molecular-electronic
junctions are represented, with examples of molecular structures. In figure3a, one
electrode functions as an electron donor and the other as an electron acceptor. The
electrodes are bridged by a linear chain (an alkane). In 1961, Harden McConnell wrote
down the rate constant for electron transfer across molecular bridge: kET. Ae“bl,
where l is the bridge length and b is an energy-dependent parameter characterizing
the molecule. For alkenes up to a certain length and for small applied voltages, this
approximation works well: Current through a junction decreases exponentially with
increasing chain length, and the alkanet effectively serves as a simple energy barrier
separating the two electrodes. The possible mechanisms for electron transport are
much richer for the electron donor-bridge-electron acceptor (DBA) molecular junction
of figure 3b. DBA complexes serve as models for understanding how charge transport
mechanisms in solution translate into the conductivity of solid-state molecular
junctions. In DBA complexes, the donor and acceptor sites are part of the molecule,
and the lowest unoccupied sites on the donor and acceptor components are separated
from one another by a bridging component that has molecular orbital of differing
energy. Ina process called electron-type super exchange; electrons that tunnel from
the right electrode into the acceptor state when a bias is applied may coherently
transfer to the donor state before tunneling to the left electrode. Alternatively, in holetype super exchange, the tunneling from the molecule into the left electrode might
occur first, followed by refilling of the molecular level from the right. In fact, both
processes will occur, and it is their relative rates that determine the nature of coherent
conductance through aDBA junction.7 A third possibility is that an electron from the
donor
can
jump
to
the
acceptor
due
to
either
thermal
Or electrical excitation. Those incoherent, diffusive processes quite closely related to
ohmic
charge
flow.
DBA junctions illustrate some of the beauty and richness of molecular electronics.
From
a
chemistâ„¢s
perspective,
The diversity of conduction mechanisms represents an opportunity to manipulate the
electrical properties of junctions through synthetic modification. The observed
conduction in DBA molecular junctions usually differs radically from that in traditional
ohmic wires and can more closely resemble coherent transport in mesoscopic
structures. Key factors include a dependence on the rates of intermolecular electron
transfer between the donor and acceptor sites. This dependence can be exploited:
The donor and acceptor components could be designed to differ energetically from
one another (as in figure 3b), so that even with no applied bias voltage, the energy
landscape
is asymmetric. Under some conditions, the conductance of a DBA junction can vary
with the sign of the applied voltage; such junctions represent a molecular approach
toward controlling current rectification.8The competition between charge transport
mechanisms through a DBA molecule can also be affected by the bridge. Shorter
bridges produce larger amounts of wave function overlap between the donor and
acceptor molecular orbitals. For a short bridge (5“10 Ã…), the super exchange
mechanism will almost always dominate. For sufficiently long bridges, the hopping
mechanism wills almost always dominate. The molecular structure of the bridge can be
synthetically varied to control the relative importance of the two mechanisms. For
example, in a bridge containing conjugated double bonds, low-lying unoccupied
electronic states within the bridge will decrease in energy with increasing bridge length
(DEB of figure 3b is lowered) and will thereby decrease the activation barrier to
hopping. Because double bonds, both in chains and in rings, facilitate charge
delocalization, they are very common in molecular electronics. Certain molecules will
isomerism”that is, change shape”upon receiving a charge or being placed in a
strong field, and in many cases, such transformations can be tightly controlled.
Different molecular isomers are characterized by different energies and possibly by
different relative rates for the hopping and super exchange transport mechanisms.
Driven molecular isomerization therefore presents opportunities for designing switches
and other active device elements.1Molecular quantum dots (figure 3c) represent a
simpler energy level system than DBA junctions, and have become the model systems
for investigating basic phenomena such as molecule“electrode interactions and
quantum effects in charge transport through molecular junctions. Representative
molecules contain a principal functional group that bridges two electrodes. Early
versions of these devices utilized mechanical break junctions―essentially fractured
gold wire that forms a pair of electrodes―in at wo-terminal device configuration.9
Although those experiments were a tour de force in terms of device preparation, small
structural variations from device to device, which translate into large conductance
changes, make quantitative interpretation of the data very difficult. More recent
experiments have employed an electrical break junction together with a gate electrode.
The gate can be used to tune the molecular energy levels with respect to the Fermi
levels of the electrodes and thus somewhat normalize the device-to-device fluctuations
that
often
characterize
two electrode measurements. An equally important advantageous that the gated
measurements, when carried out at low temperatures, can resolve the molecular
energy levels to a few meV. Such resolution allows, for example, measurements of the
signatures of electron-vibration coupling. Two recent papers reported on a unique
quantum effect known as a Kondo resonance (see figure 4) in organic molecules
containing paramagnetic metal atoms.3 That this resonance was designed by
chemical synthesis into two different molecules, and was observed in single-molecule
transport measurements, represents a spectacular success for molecular electronics.
Electrode
effects
The molecule“electrode interface is a critically important component of a molecular
junction: It may limit current flow or completely modify the measured electrical
response of the junction. Most experimental platforms for constructing molecularelectronic devices are based on practical considerations. This pragmatic approach is,
in many ways, the boon and the bane of the field. For example, the sulfur“gold
bond is a terrific chemical handle for forming self-assembled, robust organic
monolayer on metal surfaces. Other methods, such as using a scanning probe tiptop
contact the molecule, are frequently employed; in part because they avoid processing
steps that can damage or unpredictably modify the molecular component. Ideally, the
choice of electrode materials would be based not on the ease of fabrication or
measurement, but rather on first principles considerations of molecule“electrode
interactions.
However,
the
current
state
of
the
art
for
the
theory
of
molecule“electrode interfaces is primitive. Poor covalent bonding usually exists
between the molecule and electrode. Consequently, at zero applied bias some charge
must flow between molecule and electrodes to equilibrate the chemical potential
across the junction. That flow can cause partial charging of the molecule, and local
charge buildup gives Scotty-like barriers to charge flow across the interface. Such
barriers, which can partially or fully mask the moleculeâ„¢s electronic signature,
increase for larger electro negativity differences. For this reason―and others,
including stability, reproducibility, and generality―chemical bonds such as
carbon“carbon or carbon“silicon will likely be preferred over gold“sulfur
linkage sat the interfaces. Very little theory exists that can adequately predict how the
molecular orbitalâ„¢ energy levels will align with the Fermi energy of the electrode.
Small changes in the energy levels can dramatically affect junction conductance, so
understanding how the interface energy levels correlate is critical and demands both
theoretical and experimental study. A related consideration involves how the chemical
nature
of
the
molecule“electrode
interface
affects
the
rest
of
the
Molecule. The zero-bias coherent conductance of a molecular junction may be
described as a product of functions that describe the moleculeâ„¢s electronic structure
and the molecule“electrode interfaces (see box 1 on page 46). However, the
chemical interaction between the molecule and the electrode will likely modify the
moleculeâ„¢s electron density in the vicinity of the contacting atoms and, in turn,
modify the molecular energy levels or the barriers within the junction. The clear
implication (and formal result) is that the molecular and interface functions are
inseparable
and
thus
muster
considered
as
a
single
system.
Conductance
through
DNA
Figure 3d represents the case of two electrodes bridged by a large molecule
containing several functional groups. Of the four junction types illustrated in figure 3,
this is the most general and interesting. Consider a protein that spans cell membrane
and shuttles information across that membrane. The protein self-assembles and self
orientsin the membrane; it recognizes and binds to other very specific proteins; it also
might switch between two forms, only one of which will transmit the chemical signal.
Proteins are large molecules, and, indeed, a certain molecular size is required to
achieve such a rich combination of properties. The rotaxane molecule shown in figure
3dmight appear large and complex, but it is actually small and efficiently designed,
given the set of mechanical, chemical, and electronic properties that have been built
into it. DNA oligomers represent perhaps the best-studied experimental example of
this category. In addition to its biological importance and its use as a synthetic
component of molecular nanostructures, the DNA molecule is of interests a charge
transfer species.4 here the relationship between intermolecular electron transfer rates
in solution and solid-state molecular junction transport becomes crucial to our
understanding of transport processes. Connections to electrodes are also of great
importance. Intramolecular electron transfer rates in DNA have been extensively
investigated in solution *ok*, and it is now becoming clear that the underlying
processes exhibit large mechanistic diversity. In general, for very short distance motion
(over a few base pairs), coherent tunneling can occur. For transfer over more than six
or seven base pairs, inelastic hopping has been strongly suggested. The fundamental
motion of electrons or holes from one site to another very broadly follows the standard
model developed by Rudy Marcus, Noel Hush, and Joshua Jortner for charge transfer
rates. The model assumes that for a charge tunneling from a donor to an acceptor site,
the tunneling parameters”the height and width of the tunnel barrier”are
modulated by interactions with a bath of harmonic oscillators that account for the
chemical
environment.
Exponential decay in the conductance with increasing distance has been seen directly
in DNA molecules folded into hairpin shapes, and the transition to incoherent hopping
has been seen in measurements of the efficiency with which holes are transferred
along the molecule. The rich mechanistic palette observed for DNA charge transfer is
becoming well understood due to elegant experiments and theory (see, for instance,
figure 5).4,10 Indeed, the early suggestions that, because of its broad range of
mechanistic possibilities, DNA might act as a paradigm for electron transfer generally
seem
to
be
correct.
Electrical transport in DNA molecular junctions is much messier―as should be true
for any molecular junction of the type represented in figure 3d. If the measurements
and systems were well defined, the junction conductance through functionally diverse
*OK* molecular systems would still be complex. Electrode mixing, structural dynamics
and disorder, geometric reorganization, and sample preparation all add to the
intricacies. As a result, the measurements are difficult to interpret, and appropriate
extensions to theory are not really available. For example, in the past two years,
reports in reputable journals have stated that DNA acts as an insulator, a
semiconductor, a metal, and a superconductor. Most probably, transport in DNA
junctions will show that the molecule (or at least naturally occurring DNA) is essentially
a wide-band gap semiconductor characterized by localized hole hopping between the
low-energy guanine“cytosine (CG) pairs (G yields the most stable positive ion).
Because the band gap is large, DNA appears uncolored and long-range coherent
charge
motion
is
improbable.
Significant
effects
should arise from various other processes, such as polar on-type hopping, in which
charge motion is accompanied by molecular distortion; Anderson type charge
localization, caused by the difference in energy between electrons localized on GC
and
adenosine“thymine
(AT)
pairs; structural reorganization; counter-ion motion; and solvent dynamics. The
available data are, more or less, consistent with the suggestion by Cees Dekker and
his collaborators that DNA is a wide-band gap semiconductor11 that can exhibit
activated transport for relatively short distances (less than 10 nm or so) but effectively
behaves as an insulator at distances exceeding 20 nm. The complexity and richness of
DNA junction behavior typify the challenge that the molecular electronics community
faces
in
Molecular
predicting
and
understanding
transport
electronics
in
molecular
junctions.
circuits
The power of chemical synthesis to design specific and perhaps even useful device
behaviors is rapidly being realized. The ensuing question, what sorts of circuit
architectures can best take advantage of molecular electronics, is now receiving quite
a bit of attention both from computer scientists (who have published largely in the
patent literature) and from experimentalists; progress toward identifying and
constructing working molecular electronics circuitry has advanced quickly. The
proposed circuit architectures have attempted to deal with five key issues: scalability to
near
molecular
dimensions; tolerance of manufacturing defects; introduction of non-traditional
fabrication methods, such as chemically directed assembly; bridging between device
densities potentially achievable at the molecular scale and those associated with
standard lithography; and fabrication simplicity. The dominant circuit structure that has
arisen from those considerations is the crossbar, 12, which is essentially an expanded
ticktacktoe board, formed from wires and having individual molecular or molecularscale devices sandwiched within the junctions. The crossbar is an intrinsically versatile
circuit and is tolerant of manufacturing defects. Both memory and logic circuits have
been demonstrated from molecular electronics and Nan wire crossbars.1, 13Arapidly
developing area of architectural research involves stitching together a patchwork quilt
of different types of crossbars with the goal of configuring an efficient computational
platform.14 Box 2 (above) illustrates how such a patchwork integrated-circuit
architecture might be laid out and presents some detail on the simplest of the circuit
components―a molecular-electronic random access memory. This particular circuit
satisfies
Crossbars
all
five
and
of
the
key
Demultiplexers
One of the most attractive architectures for designing molecular-electronics circuits for
computational applications and interfacing them to the macroscopic world is the
crossbar. The general concept is shown on the left, where a sort of patchwork quilt of
logic, memory, and signal routing circuits is laid out. The simplest of these
circuits―and one that has-been experimentally demonstrated―is a memory
circuit.
The memory, shown on the right, consists of two major components. The central
crossbar”the crossing of16 vertical and 16 horizontal black wires”constitutes a
256-bit memory circuit. Bitable molecular switches are sandwiched at the crossings of
the densely patterned Nan wires, and each junction can store a single bit. Each set of
the larger blue wires is arranged into what is called a binary tree multiplexer. The
multiplexers here adopt some interesting architectural variations that allow them to
bridge from the micron or sub micron scale of the blue wires to the nanometer scale of
the black wires. Each multiplexer consists of four sets of complementary wire pairs,
designed to address 24 nano wires. The scaling is logarithmic: 210nanowires, for
example, would require only 10 wirehairs for each multiplexer. One wire within each
pair has an inverted input; a 0 input, for example, sends one wire low and its
complement high. Along each blue wire is a series of rectifying connections (gray bars)
to the Nan wires; each pair of wires has a complementary arrangement of connections.
When a given address (0110, for example) misapplied, the multiplexer acts as a fourinput AND gate so that only when all four inputs are high does a given Nan wire go
high. The orange bars indicate how one wire (red) is selected by each multiplexer. At
the upper right is shown more detail for a multiplexer wire that selects a pattern of four
connects followed by four opens. Note that the separation between the individual
contacts is much larger than the pitch of the nano wires; that larger separation greatly
reduces the fabrication demands. Note also that the frequencies of the patterns of
connections are important, but not the absolute registry: Each nano wire is uniquely
addressable, but the mapping of addresses to nanowires is not important. Those two
characteristics allow the architecture to bridge the micron or submicron length scales
of lithography to the nanometer length scales of molecular electronics and chemical
assembly.
Molecular
electronics
devices.
(a) This optical micrograph shows a collection of 64-junctionmolecular circuits,
fabricated by a combination of soft-imprinting techniques for the wires and chemical
assembly
for
the
molecules
at
the
wire
intersections.
(b) An atomic force micrograph of one of the circuits, which could be used either as a
random access memory or as a combination logic and memory circuit. The molecules
used
The
in
this
future
circuit
of
are
molecular
bitable
relaxants
electronics
The fundamental challenges of realizing a true molecular electronics technology are
daunting. Controlled fabrication to within specified tolerances―and its experimental
verification―is a particular problem. Self-assembly schemes based on molecular
recognition will be crucial for that task. Fully reproducible measurements of junction
conductance are just beginning in labs at Cornell, Harvard, Delft, Purdue, and
Karlsruhe Universities and at the Naval Research Laboratory and other centers. There
is a real need for robust modeling methods to bridge the gap between the synthesis
and understanding of molecules in solution and the performance of solid-state
molecular devices. Additional challenges involve finding fabrication approaches that
can couple the densities achievable through lithography with those achievable through
molecular assembly. Controlling the properties of molecule“electrode interfaces
and constructing molecular electronic devices that can exhibit signal gain are also
problems. Rapid progress is being made to address these challenges. Voltage-gated,
single-molecule devices may emerge as*OK* the high-resolution spectroscopy tool
that will eventually link experiment and theory. Binary tree multiplexers, such as the
one presented in box 2, have the potential to bridge sub micron to nanometer length
scales.15Nanowire field-effect transistors have demonstrated gain, and so the
challenge may be one of integration of multiple device types rather than discovery of
new devices. But no molecular electronics logic or memory device has been tested
against any of the abilities: reliability, temperature stability, and the like. Many of the
technology goals of molecular electronics, such as the computational applications
discussed in this article, should probably be viewed as drivers for steering the field
forward and for defining the critical and rate limiting challenges that must be overcome.
If, for example, someone does demonstrate a robust, energy-efficient computational
platform based on molecular electronics, interfaced to the outside world, and
fabricated at a device density between 1011 and 1012 cm“2, we will have made so
many fundamental advances that it would be surprising if some computational
application is even the most useful result of such work. Interfaces to bios stems, ultra
dense single-molecule sensor arrays, and pathways toward molecular mechanical and
Nan mechanical devices are among the likely beneficiaries of the successful
development
of
molecular-electronic
integrated
circuitry.
Towards Molecular Electronics: New Way of Making Molecular Transistors
Scientists have long been intrigued by carbon nanotubes, tiny straws of pure carbon
measuring less than a hair's width across. Successfully linking them in stable
arrangements would allow for an impressive increase in both the speed and power of a
variety of electronics. This new research at Columbia sets the stage for advances in
real-time diagnosis and disease treatment, surgical robotics, and information storage
and
retrieval,
potentially
rendering
room-sized
supercomputers
obsolete.
In the Jan. 20, 2006, issue of Science, Columbia scientists explain how they have
developed a unique way to connect the ends of carbon nanotubes by forming robust
molecular bridges between them. The Columbia team was able to combine the best
qualities of carbon nanotubes and organic molecules in a single electronic switch, the
journal
reported.
Previously, researchers working in this area of nanotechnology have made transistors
out of carbon nanotubes with switches connecting molecules to metal wire leads. This
Columbia research illustrates a more elegant way of making molecular transistors,
since the nanotube leads are already the same size as the molecules, and they are
made
of
carbon,
making
it
easier
to
connect
them
chemically.
This new method of wiring molecules into the gaps of single-walled carbon nanotubes
employs oxidative cutting -- a lithographic technique that makes each cut-end of the
nanotube more prone to molecular bonding. These new methods of constructing
molecular bridges could one day revolutionize the size and scale of computer
hardware
"Molecular electronics has real-world relevance," says Colin Nuckolls, an associate
professor of chemistry, and a co-author of the Science paper. "It opens the door to
new types of ultrasmall switches and sensors. We are able to form a bridge, both
literally and figuratively, by combining reaction chemistry with ultrafine lithography."
The nanotubes themselves are long, thin cylinders of carbon unique for their size,
shape and physical structure. They can be thought of as a sheet of graphite forming a
hexagonal lattice of carbon, (see image) rolled into a tube, explains Columbia senior
research scientist Shalom Wind, another co-author of the paper. They have been
shown to possess remarkable mechanical and electronic properties, he added.
Attaching molecular wires to single-walled nanotubes involves cutting a tube using
nanolithography combined with a localized oxidation process that leaves a nanotube
with two ends that are capped with carbon-based acid groups and separated by a
molecule-sized gap. In that tiny space, a molecule can be chemically joined with each
end to form a robust nanotube/molecule complex, which operates as a nanoscale
transistor.
The nature of this work is also expected to keep alive "Moore's Law," the prediction
made in 1965 by Intel co-founder Gordon Moore who predicted the number of
transistors per square inch on integrated circuits would double every year. Moore said
the trend would continue for the foreseeable future; but without an order-of-magnitude
shift in the scale of computer circuitry -- a promise represented in Columbia's latest
work“that prediction could hit a wall in the next decade, experts say.
ADVANTAGES
¢
Tiny
¢
¢
¢
Low
Able
power
to
integrate
consumption
large
circuit
Re-configurable
DISADVANTAGES
¢
Controlled
¢
fabrication
within
Hard
specified
tolerances.
experimental
verification.
APPLICATIONS
¢
Sensors
¢
Displays,
Energy
¢
Smart
Material,
¢
Molecular
Motors,
transduction
devices
scale
transistors
Molecular
Logic
and
memory
devices
CONCLUSION
Molecular electronics clearly has the advantage of size. The components of these
circuits are molecules, so the circuit size would inherently range between 1 to 100 NM.
Molecular systems, or systems based on small organic molecules, possess interesting
and useful electronic properties. The rapidly developing area of organic -or plasticelectronics is based on these materials. The investigations of molecular systems that
have
been
performed
in
the
past
have
been
strongly
influenced.
Molecular electronics is reaching a stage of trustable and reproducible experiments.
This has lead to a variety of physical and chemical phenomena recently observed for
charge currents owing through molecular junctions, posing new challenges to theory.
The potential application of molecular electronics has already attracted the interest of
some
large
corporate
REFERENCE
http://www.calmec.com
http://www.wikipedia.org
"An Overview of the First Half-Century of Molecular Electronics" by Noel S. Hush, Ann.
N.Y.
Acad.
Sci.
1006:
1“20
(2003).
http://www.physicstoday.org
CONTENTS
¢
INTRODUCTION
¢
HISTORY
¢
¢
MOLECULAR
ELECTRONICS
WHY
TECHNOLOGY
MOLETRONICS
¢ TRANSCENDING MOORE™S LAW WITH MOLECULAR ELECTRONICS
¢
¢
MOLECULAR
CHARGE
ARCHITECTURES
FOR
TRANSPORT
DESIGNING
AND
ELECTRODE
MOLETRONICS
EFFECTS
CIRCUITS
¢
ADVANTAGES
¢
DISADVANTAGES
¢
APPLICATION
¢
¢
FUTURE
OF
MOLETRONICS
CONCLUSION
¢ REFERENCE
molecular electronics semina report.DOC (Size: 148.5 KB / Downloads: 551)
Molecular Electronics abstract.doc (Size: 91 KB / Downloads: 352)
ABSTRACT
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circu
smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the are
molecules will be hundreds of times smaller than their semiconductor based counterparts.
Moreover individual molecules are easily made exactly the same by billions & trillions. The dramatic reduct
promised by the field of molecular electronics.
INTRODUCTION
Will silicon technology become obsolete in future like the value technology done about 50 years ago? Scien
a relatively new field, which emerged as an important area of research only in the 1980â„¢s. It was through
Conventional electronics technology is much indebted to the integrated circuit (IC) technology. IC technolog
gradual increased scale of integration, electronics age has passed through SSI (small scale integration), MSI
integration). These may be respectively classified as integration technology with 1-12 gates, 12-30 gates, 30
The density of IC technology is increasing in pace with Famour Mooreâ„¢s law of 1965. till date Mooreâ„¢s
wrote in his original paper entitled ËœCramming More Components Onto Integrated Circuit â„¢, that, the co
year .certainly, over the short term, this rate can be expected to continue, if not to increase. Over the longer t
will not remain constant for at least ten more years.
It is now over 30 years since Moore talked of this so called technology-mantra. it is found that I.Câ„¢s are fo
prediction was based on a survey of industries and is believed to be correct with research of properties of sem
competitive to semiconductor technology.
This new technology is known as Molecular electronics. Semiconductor integration beyond ULSI, through c
like quantum effects, etc.
For a scaling technology beyond ULSI, prof.Forest Carter put forward a novel idea. In digital electronics, ˜
ËœONâ„¢ and ËœOFFâ„¢ conditions of a switching transistor. Prof. Carter postulated that instead using a tr
represent the two states, namely YES & NO of digital electronics.
For e.g. one can use positive spin & negative spin of a molecule to represent respectively ËœYESâ„¢ & ËœN
proposed to be used, the scaling technology may go to molecular scale. It is therefore defined as MSE (mole
In order to augment his postulation Prof. Carter conducted a number of international conferences on the sub
However, as of today, molecular electronics is a broad field. The field is a result of a search for alternative m
The field is a challenge but not a replacement for inorganic electronics on immediate terms. Molecular elect
non-linear optics and biologically important materials in the field of electronics. Therefore hopes run high fo
computers with inbuilt thinking functions and bio-chips etc..
In the field of communication the role of optical soliton, which is a by product of non-linear optics, will be u
networks. Economic solar cells are another existing promise of molecular electronics.
Molecular electronics, which is a high investment and high-risk field, is at the same time a highly promising
the cost molecular systems shall be cheaper. The prospects of molecular electronics depend on the successfu
physics, chemistry, biology, material science, etc.
Historically the concept of molecule electronics dates back to the last century. The familiar e.g. is the use of
started working on organic solids as alternative semiconductors because of their attractive optical properties
Carter who conducted in 1980â„¢s a number of international conferences on the subject mainly initiated the
progress of molecular electronics has always been smooth, the prospects of the future have vastly improved.
ORGANIC DEVICES
Molecular Electronics, as on date, can be divided into broad areas: Molecular materials of electronics (MME
properties of molecules or macro molecules or organic materials in electronic devices. MSE deals with micr
molecules for application in electronics. The main categories of MME are organic semiconductors or molec
materials, photo and electro-chromic materials, non-linear optical materials and biologically important mate
The use of molecular organic materials as active elements in electronic devices was actually augmented with
versatile and easy to process. These properties, along with the electrical property of conducting polymers tha
make the polymer a material of hot current research.
But the basic question is whether molecular organic materials will behave like real semi conductors. If any m
carrier mobility and demonstrate the existence of controllable band gap of the order of 0.75 to 2 eV. Till dat
Typical resistivity
Here it can be pertinent to mention the functioning of p-n junction. The solid state error of electronics owes
silicon. The flow of electricity can be controlled by adding impurities to silicon.
Mobilities are seen to be low in molecular organic materials. Polymers took a leading high mobility charge c
too inhomogeneous to access experimental high mobilities. Despite this, the conjugated or conducting polym
synthesized conducting polymers could be employed as either metallic or semi conducting component of a m
rectification ratios in excess of thousands
There are reports of polymer based MISFET (metal insulator semiconductor field effect transistor) devices w
quantum efficiencies in the region of 1% photons per electrons. Organics, which are intrinsically p-type in s
There are recent reports of n-type organic semiconductors. This behavior is found when T N C Q (tetracyano
field mobility has been observed as 3x10-5 cm sq / volt sec.
An active polymer transistor was first reported by Burroughes et al in 1988. the device had some important f
operating frequency was low due to low carrier mobility.
However a dramatic lead was achieved by Prof. Francis Garnier and co-workers in 1990. they reported a tot
structure comprising an oxidized silicon substrate and a semiconductor polymer layer. It has great flexibility
of organic FET from Dr.Friend and co-workers Cavendish Laboratory of Cambridge. All FETâ„¢s reported
FETs, in addition to low operating frequency. These problem need to be address before organic FETs can be
Recently, pure semi conducting polymers have channeled into display devices. These conjugated with impro
possibility that conjugated polymers would be used to manufacture LEDs out of plastic. This has immense a
stumbling blocks which are yet to be overcome are efficiency and life time. LEDs should have at least 10%
minimum of 10000 hrs lifetime is required for flat screen or panel displays till date, the maximum life of pol
Organic materials have not being able to compete with silicon or inorganic materials to form active electron
world wide trend towards organics, at least in research areas. Two of the molecules that have been used to d
carbon nanotubes.
POLYPHENYLENE“BASED CHAINS
Polyphenylene based molecular wires and switches use chains of organic aromatic benzene rings. Recently,
currents. In addition, polyphenylenes as well as similar organic molecules have been shown to be capable of
An individual benzene ring less one of its hydrogens, giving the phenyl group C6H5, can be bonded as a gro
you have two binding sites in the ring.
Polyphenylenes are obtained by binding phenylenes to each other on both sides and ending the chain-like str
molecular groups (e.g., singly-bonded aliphatic groups, doubly-bonded ethanol groups, and triple bonded eth
Polyphenylene-based aromatic molecules with useful structures and properties. Recently, sensitive experime
electricity. In one experiment, an electrical current was passed through a monolayer of approximately 1,000
adsorbed to metal contacts on either end. The system was prepared so that all the molecules of the nanopore
current that passed through the molecular-wires was 30 mA, or about 30 nA per molecule. This works out to
based molecular wire.
For comparison, a larger molecule, the carbon nanotube (bucky tube) has been measured transmitting curren
polyphenylene-based molecular-wires do not carry as much current as the bucky tubes however, because of
carbon nanotubes. These current densities are quite high - about a half a million times greater than that of a c
Polyphenylene-based molecules also have the advantage of a well-defined chemistry, synthetic flexibility, a
techniques for conductive polyphenylene-based chains have been refined by J.M. Tour who has made mole
Tour wires".
The way energy is transferred or channeled from one end of a molecule to the other is via p-type orbitals lyi
length of the molecule thus connecting with the neighboring molecule creating a polyphenylene-based chain
maintained.
Polyphenylene-based molecules bonded with multiply bonded groups (such as ethenyl, -HC=CH-, or ethyny
can be inserted as spacers between phenyl rings in a Tour wire. Spacers are needed to eliminate steric interfe
extent of p-orbital overlap between adjacent rings thereby reducing conductiveness.
CARBON-NANOTUBES
A second type of molecule that can be used for a molecular electronic backbone is the carbon nanotube or b
structures make a very conductive wire. They differ in diameters and chiralities and come in a range of cond
are fairly new to the world of chemistry having only been discovered and characterized in the last two decad
Once made, carbon nanotubes are stable but they are made only under extreme conditions. Their synthesis is
To get the precision required to function in electronic circuits, the use of physical inspection and manipulati
purpose.
Currently, the molecular electronic community is in a situation where the most chemically flexible molecula
the carbon nanotube, is not the most flexible chemically. Development has been undertaken by several resea
two particular components, aliphatic molecular insulators and diode switches, that in concept can be used w
Aliphatic Molecular Insulators
Aliphatic organic molecules have nodes in their electron densities above the atomic nuclei. For this reason, t
enables aliphatic molecules or groups to act like resistors.
Diode Switches
A diode is a two terminal device in which current may pass in one direction through the device, but not the i
important types of molecular-scale diode switches have been demonstrated: rectifying diodes and resonant t
Rectifying Diodes
Rectifying diodes, also called molecular rectifiers, use structures that make it more difficult for an electric cu
A, than it is to go the opposite forward direction from A to B. Rectifying diodes have been elements of analo
role in the forming and testing of strategies for molecular scale electronics. In fact, the first theoretical paper
Ratner that appeared in the journal Chemical Physics Letters in November 1974. But it was only in 1997 tha
rectifiers. One group was led by R.M. Metzger at the University of Alabama and the other led by M.A. Reed
Resonant Tunneling Diodes (RTDs)
Unlike the rectifying diode, current can pass just as easily in both directions through an RTD. The RTD uses
to control the diode so as to switch current on and off, and so as to keep electrical current going from the sou
synthesized by Tour and demonstrated by Reed. The device is a molecular analog of a larger solid-state RTD
quantum-effect circuitry.
Advantages of Polyphenylene-Based Structures
With Polyphenylene-based molecules, it is relatively easy to propose complex molecular structures that are n
synthesized. For their size, polyphenylene-based molecular devices conduct an impressive current of electro
Tour-wire-based molecular digital logic has another advantage. Since polyphenylene-based molecules are so
and operated, they will represent the ultimate in digital electronic logic miniaturization. Any other structure
REALIZATION OF BASIC CIRCUITS
Molecular AND and OR Gates Using Diode-Diode Logic
The circuits for the AND and OR digital logic gates which use diode-diode logic structures have been know
measure about 3 nm x 4 nm. That area is about one million times smaller than would be the area of a corresp
Molecular XOR Gates Using Molecular RTDs and Molecular Rectifying Diodes
To complete the diode-based family of logic gates, you need a NOT gate. To make a NOT gate with diodes,
polyphenylene-based rectifying diodes, an XOR gate measuring about 5 nm x 5 nm can be built. The three s
the insertion of the molecular RTD, the molecular circuit for the XOR gate is similar to the OR gate. The XO
voltage) at both inputs. This shuts off current flow through the RTD and makes the XOR gateâ„¢s output 0,
which can be made the same as the complete set AND, OR, and NOT.
Molecular Electronic Half Adder
With a complete set of molecular logic gates, larger structures can be made that implement higher binary dig
XOR gates and measuring only 10 nm x 10 nm. When currents and voltages representing two addends are p
two inputs that split the current introduced so that the current passes through both of the logic gates regardle
separate outputs. By using an out-of-plane connector structure, an in-plane molecular wire can be passed ov
split, signal loss should not be a problem because the signal is recombined on the output side of the structure
lead that goes to the ground to help minimize signal loss.
Molecular Electronic Full Adder
By combining two half adders plus an OR gate, you can make a molecular electronic full adder measuring a
Combining Individual Devices
By bonding together existing functional devices, it is thought that devices of higher functions can be made. B
themselves. The characteristic properties of each device will in general be altered by the quantum wave inter
well. Software is being developed to deal with quantum mechanical issues so that complete molecular electr
CHARACTERISTICS OF MOLECULAR DEVICES
Nonlinear I-V Behavior
Unlike solid-state electronics, the I-V behavior of a molecular wire is nonlinear. Some molecular devices wi
Energy Dissipation
When electrons move through a molecule, some of their energy can be lost to other electrons motions and th
energy levels of the molecule and how they interact with the moleculesâ„¢ vibrational modes. Depending on
large.
Gain in Molecular Electronic Circuits
In large molecular structures deploying molecular devices with power gain, such as molecular transistors, th
maintain signal-to-noise ratio, and to achieve fan-out.
Speeds
Energy dissipation relates closely to the speed at which a molecular electronic circuit can operate. If strong c
would be needed to ensure the reading of a bit. This would require more time. Because of their scale and den
to be highly important. The molecular half-added described earlier is one million times smaller than one in a
Optical information technology
The ever growing demand of increased computing speed is mainly limited by memory accessing time and st
the ultimate speed.
Photo chromic materials show a bistable property. They undergo reversible color changes under irradiation a
order to build a three-dimensional optical memory, appears appropriate to build a three-dimensional optical
conceptualized.
With the advent of optical fiber communication an interest in components for processing optical signals has
technology such as problems of parasitic capacitance, inductance and resistance, less reliability and power d
optical computers where full advantage of the fundamental speed of light is proposed to be achieved. Nonlin
which has potential applications in computer communication and information technology. Current research h
materials. Discovery of laser in 1960s has given a thrust to the research of NLO materials and their applicati
Nonlinearity can be used basically in two ways for electronic devices: frequency conversion and refractive i
be used for second harmonic generation, frequency mixing and parametric amplification, etc. the prime inter
Molecular Scale Electronics
The quest for ever decreasing size but more complex electronic component with high speed ability gave birt
was put forward by Carter, who proposed some molecular analogues of conventional electronic switches, ga
Rather. MSE is a simple interpolation of IC scaling. Scaling is an attractive technology. Scaling of FET and
Silicon technology has offered us SSI, LSI, VLSI and finally we have ULSI. Such technologies make even t
transistors on a chip is over. But there are some problems now in further scaling in silicon technology. For in
density.
MSE is a remedial measure. Molecules possess great variety in the structure and properties. Therefore findin
electronics is possible the study of a single molecule is not a problem now as we have STM (scaling tunnelin
Upcoming trends
At some of the top laboratories around the country, scientists are publicly expressing beliefs that before now
revolution where molecules will be used in place of semiconductors, creating electronics circuit small that th
computing speed and memory resulting from circuits so small would stagger virtually all fields of technolog
successfully created molecular size switches that can be opened and closed repeatedly. The HP/UCLA group
to build functioning digital computers. These breakthroughs in the field of molecular electronics seem to be
There are several research groups working in laboratories under top-secret conditions. They are making prog
Memory (RAM). RAM, on a molecular scale, could offer incredibly huge storage capacities. Molecular met
scale of such devices, it might be possible to store, for e.g., a DVD movie on something the size of a grain o
The micro electronic devices on todayâ„¢s silicon chips have components that are 0.18 microns in size or ab
hundred nanometers. In molecular electronics, the components could be as tiny as 1 nanometer. This would
incorporated into all manmade items.
The semiconductor world predicts it will continue to advance the silicon based chip, making ever smaller de
Currently semiconductor chips are made in multibillion dollar fabrication plants by etching circuitry into lay
requires huge amounts of money to upgrade to newer fab-plants. The world of computers is in for a change.
Several computer semiconductor companies, including Sun Microsystems and Motorola have been meeting
electronics.
Researches say that this is still only the beginning in the making of molecular computers. There are still man
Some researches believe that in order for molecular systems to work as computers, they will need to have fa
The progress made recently has caused a lot of excitements among researches in molecular electronics. For a
the future and have results that are helping to map the way for them.
CONCLUSION
The subject of molecular electronics has moved from mere conjuncture to an experimental stage. Research i
information explosion. Polymer materials hold hopes of rapid development of improved systems and techniq
polymer optical fibre has a number of advantages over glass fibres like better ductivity,light weight, higher f
vital role in the coming years and MSE shall compete with IC technology which is growing in accordance w
REFERENCES
[1]. T. Rueckes, K. Kim, E. Joselevich, G.Y. Tseng, C.-L. Cheung, and C.M. Lieber "Carbon Nanotube-Bas
(2000).
[2]. "Large-scale synthesis of carbon nanotubes", T W Ebbesen and P M Ajayan Nature, vol.358, p220 (199
[3]. Scientific forum http://www.calmec.com/scientif.htm
[4]. Search http://www.calmec.com/search.htm
[5]. http://www.ieee.org
CONTENTS
1. INTRODUCTION
2. ORGANIC DEVICES
3. POLYPHENYLENE“BASED CHAINS
4. CARBON-NANOTUBES
5. REALIZATION OF BASIC CIRCUITS
6. CHARACTERISTICS OF MOLECULAR DEVICES
7. UPCOMING TRENDS
8. CONCLUSION
9. REFERENCE