MOLETRONICS

A SEMINAR REPORT

Submitted to

SSM COLLEGE OF ENGINEERING AND TECHNOLOGY

By

KAIFAT SIDIQ THAKUR

ENROLLMENT: 5555

In partial fulfillment for the award of the degree of

BACHELOR OF ENFINEERING

In
ELECTRONICS AND COMMUNICATION ENGINEERING

DEPARTMENTOFELECTRONICS AND COMMUNICATIONENGINEERING

SSM COLLEGEOF ENGINEERING AND TECHNOLOGY
DIVAR PARIHASPORA PATTAN.

NOV 2018

DEPTT OF ELECTRONICS AND COMMUNICATION Page 1

 SSM COLLEGE OF ENGINEERING AND TECHNOLOGY

DIVAR PARIHASPORA, PATTAN.

CERTIFICATE

This is to certify that the seminar report entitled “MOLETRONICS” is a paper

presented by KAIFAT SDIQ THAKUR bearing enrollment number 5555 in

partial fulfillment for the award of Degree of Bachelor of Engineering in

Electronics and Communication Engineering.

ER. MANZOOR AHMAD MIR Er. SAYIEMA AMIN

H.O.D (Department of E&C) Seminar coordinator

DEPTT OF ELECTRONICS AND COMMUNICATION Page 2

 ACKNOWLEDGEMENT
This seminar report was supported and guided by Er. SAYIEMA AMIN I’d like to thank my
teachers and fellow students from SSM COLLEGE OF ENGINEERING, DEPARTMENT OF
ELECTRONICS AND COMMUNICATION ENGINEERING who provided insight and expertise that
greatly assisted the research.
I would like to express my heartfelt gratitude to the HOD, DEPARTMENT OF ELECTRONICS AND
COMMNICATION ENGINEERING Er. Manzoor Ahmad Mir for acceptance and encouragement of
more conservative matters in the said field. I also express my deep gratitude to our teachers and
staff at the Department of electronics and communication who were always of great help and
supportive in every nature. This wasn’t possible without the supportive nature and helpfulness of
the department of electronics and communication
Abstract

Molecular electronics (moletronics) represent the ultimate challenge in device

miniaturization. The concept of molecular electronics has aroused great excitement,
both in science fiction and among scientists. This is because of the prospect of size
reduction in electronics which is offered by molecular-level control of properties.
Molecular electronics provides means to extend Moore’s Law beyond the foreseen
limits of small-scale conventional silicon integrated circuits.
It implements one or a few molecules to function as connections, switches, and other
logic devices in future computational devices.
Moletronics has following advantages over semiconductor devices:
1) Low Power Consumption.
2) Small and compact size.
3) High Speed
4) Low Cost
5) Low Temperature Manufacturing
6) Stereochemistry can be applied
7) Synthetic Flexibility is there
Moletronics has got a wide range of scope applications.
Till now we have created Switch and Memory units from a single molecule.With
more research we will soon be able to find smaller devices which are faster, cost
effective, having large battery life .
TABLE OF CONTENTS

S.No. TOPICS Page No

1 INTRODUCTION 5

2 BACKGROUND 6

3 ADVANTAGES OF MOLETRONICS 7

4 MOLECULAR ELECTRONIC SYSTEMS 10

4.1 Electronic Structures 312
4.2 Different Alligator Clips in SAMs 14
4.3 Electrode Effects 13

5 Applications of Molecular Electronics 14

5.1 Switch using Moltronics 17
5.2 Memory Chip 19
5.2.1 Memory Hold Time 19

6 Future of Molecular Electronics 21

7 REFERENCES 23
1. Introduction

Molecular electronics, also called moletronics, is an interdisciplinary subject that

spans chemistry, physics and materials science. The unifying feature of molecular
electronics is the use of molecular building blocks to fabricate electronic
components, both active (e.g. transistors) and passive (e.g. resistive wires). The
concept of molecular electronics has aroused great excitement, both in science fiction
and among scientists. This is because of the prospect of size reduction in electronics
which is offered by molecular-level control of properties. Molecular electronics
provides means to extend Moore’s Law beyond the foreseen limits of small-scale
conventional silicon integrated circuits.

“Molecular electronics” is a poorly defined term. Some authors refer to it

as any molecular-based system, such as a film or a liquid crystalline array. Other
authors, including Tour J. M., prefer to reserve the term “molecular electronics”
for single-molecule tasks, such as single molecule-based devices or even single
molecular wires. Due to the broad use of this term, molecular electronics are split
into two related but separate subdisciplines by Petty M. C.: molecular materials
for electronics utilizes the properties of the molecules to affect the bulk properties
of a material, while molecular scale electronics focuses on single-molecule
applications.

Molecular electronics represent the ultimate challenge in device miniaturization.

Molecular devices can have any no of termini with current-voltage responses that
would be expected to be nonlinear due to intermediate barriers or hetero
functionalities in the molecular framework while molecular wires refer to especially
tailored molecular nanostructures energetic properties. Molecular-scale devices
actually operating today include: FETs, junction transistors, diodes, and, molecular
and mechanical switches. Logic gates with voltage gain have been built, and many
techniques have been demonstrated to assemble nanometer wide wires into large
arrays. Programmable and non-volatile devices which hold their state in a few
molecules or in square nanometers of material have been demonstrated.
 MOLETRONICS 2018

2. Background

Study of the charge transfer in molecules was promoted in the late 1940s by Albert
Szent-Gyorgiand and Robert S. Mulliken.6 They discussed the so-called “donor-
acceptor” systems and then developed the study of charge transfer and energy
transfer in molecules. In 1959, Richard P. Feynman presented his lecture “There’s
Plenty of Room at the Bottom”. This famous call was for chemists, engineers and
physicists to work together and to build structures from bottom up at the molecular
level. Feynman’s suggestion spurred serious notion to the possibility of engineering
single molecules to function as elements in the
information-processing systems. This idea was tested by a 1974 paper entitled
“Molecular Rectifiers” by Mark Ratner and Ari Aviram.7 This paper illustrated a
theoretical molecular rectifier and generalized molecular conduction in molecular
electronics. They discussed theoretically the possibility of constructing a “very
simple electronic device, a rectifier, based on the use of a single organic molecule”.
It has turned out in later years that observing true molecular rectification is very
difficult. Their proposal formed a brave attempt that would strengthen the
foundations of the field with hopes of electronic applications truly at the molecular
scale. Later, in 1988, Aviram described in detail a theoretical single-molecule field-
effect transistor.8 Further concepts were proposed by Forrest Carter5 of the Naval
Research Laboratory, including single-molecule logic gates. These were all
theoretical constructs and not concrete devices. The direct measurement of the
electronic characteristics of individual molecules has to wait for the development of
new techniques which are capable of making reliable electrical contacts at the
molecular scale. This was not an easy task. The first experiment measuring the
conductance of a single molecule was only reported in 1997 by Mark Reed and co-
workers. Since then, the development of nano-scale measuring techniques has
progressed rapidly and the theoretical predictions of the early workers have mostly
been confirmed. Rapid progress in molecular electronics has been made in the last
three decades owing to advent of new characterization techniques.

DEPTT OF ELECTRONICS AND COMMUNICATION Page 7

3. Advantages of Molecular Electronics

Molecular structures are very important in determining the properties of bulk

materials, especially for application as electronic devices. The intrinsic properties of
existing inorganic electronic materials may not be capable of forming a new
generation of electronic devices envisioned, in terms of feature sizes, operation
speeds and architectures. However, electronics based on organic molecules could
offer the following advantages:

Size – Molecules are in the nanometer scale between 1 and 100 nm. This scale
permits small devices with more efficient heat dissipation and less overall production
cost to be made.

Power: One of the reasons that transistors are not stacked into 3D volumes today is
that the silicon would melt. The inefficiency of the modern transistor is staggering. It
is much less efficient at its task than the internal combustion engine. The brain
provides an existence proof of what is possible; it is 100 million times more efficient

in power/calculation than our best processors. Sure it is slow (under a kHz) but it is
massively interconnected (with 100 trillion synapses between 60 billion neurons),
and it is folded into a 3D volume. Power per calculation will dominate clock speed as
the metric of merit for the future of computation.

Assembly – One can exploit different intermolecular interactions to form a variety of

structures by the array of self-assembly techniques which are reported in the
literature. The scope of application of the self-assembly technique is only limited by
the researcher’s ability to explore.

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 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. Much of the conceptual
difference of nanotech products derives from a biological metaphor: complexity
builds from the bottom up and pivots about conformational changes, weak bonds,
and surfaces. It is not engineered from the top with precise manipulation and static
placement.

Low Temperature Manufacturing: 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.

Stereochemistry – A large number of molecules can be made with indistinguishable

chemical structures and properties. On the other hand, many molecules can exist as
distinct stable geometric structures or isomers. Such geometric isomers exhibit
unique electronic properties. Moreover, electronic properties of conformers can be
affected by pressure and temperature. We can therefore make use of stereochemistry
to tune properties.

Synthetic flexibility – Organic synthesis is extremely versatile. It provides the

means to tailor make molecules with the desired physical, chemical, optical and
transport properties. The multitude of electronic energy levels in molecules can be
fine-tuned by simple variations in molecular structure, e.g., by changing substituents
on aromatic rings in conjugated compounds. Moreover, derivatization of a molecule
can lead to improving the processibility of the material without changing the device
properties. This allows an entirely new dimension in engineering flexibility that does
not exist with the typical inorganic electronic materials.

4. Molecular Electronic Systems

In order to perform as an electronic material, molecules need a set of overlapping

electronic states. These states should connect two or more distant functional points or
groups in the molecule. A conjugated π orbital system is required for a typical
candidate of molecular electronics. This conjugated system needs to extend on an σ-
framework with terminal functional groups. Molecules for electronic applications
generally have 1-, 2-, or 3-dimensional shapes as depicted in Figure . Alligator clip,
which provides stable connection of the material to the metallic electrodes or

inorganic substrates, is the caudal functional group of the organic electronic material.
It is important to note that each part of an organic molecule used as the active
component in nano scale electronic device has their own contribution. In general, by
measuring the conductivity of a series of systematically modified molecules, the
contribution of each component can be determined. For example, by varying the
molecular alligator clip and examining the molecules’ conductivity, the contribution
of the alligator clip to the conductivity can be determined.

Schematic of 1D, 2D and 3D shapes for molecular electronics.

4.1 Electronic Structures

The simplest molecules studied in molecular electronics are the alkylthiols, which
only have σ-bonds. The others are organic molecules represented by alternating
double and single bonds or alternating triple and single bonds. These are indicative
of an σ-bonded C-C backbone with π-electron delocalization. The conjugation length
is defined as the extent over which the π- electrons are delocalized. The double or
triple bonds between carbon atoms in the molecules have an electron excess to that
normally required for just σ-bonds. These extra electrons are in the pz orbitals which
are mainly perpendicular to the bonding orbitals between adjacent carbon atoms.
These electrons overlap with adjacent pz orbitals to form a delocalized π-electron

cloud. This cloud spreads over several units along the backbone. When this happens,
delocalized π valence (bonding) and π* conduction (anti-bonding) bands with
defined bandgap are formed — which meets the requirements for (semi)conducting
behavior. Normally the electrons reside in the lower energy valence band. If given
sufficient energy, they can be excited into the normally empty upper conduction
band, giving rise to a π–π* transition. Intermediate states are forbidden by quantum
mechanics. The delocalized π-electron system confers the (semi)conducting
properties on the molecule and gives it the ability to support charge transport.
Modifications can be done based on the backbone to improve electron transfer
properties. Scheme shows several popular backbones for a 1D molecular electronic
material. Backbones for 2D and 3D molecular electronics are similar to 1D’s.

Representative structures
for 1D molecular
electronic materials;
(a) Alkyldithiol;
(b) Oligo(p-phenylene)-
dithiol
(c) (p-phenylene
ethynylene)-dithiol.
 Library of molecules under investigation
4.2 Different Alligator Clips in SAMs

Scheme 2 Representative alligator clips for forming SAMs. 1,2-dioctyldisulfane (a);

bis(4,4’-biphenyl)ditelluride (b); benzenethiol (c); benzene-1,4-dithiol (d); S-
phenylethanethioate (e); S,S’-1,4-phenylene diethanethioate (f); 4,4’-biphenyl
selenoacetate (g); phenyl isocyanide (h);1,4-phenylene diisocyanide (i); 2-nitro-1,4-
bis(phenylethynyl)benzene diazonium tetrafluoroboride (j)

Scheme 2 shows some common alligator clips used in molecular electronics for
forming SAMs. The acetyl-protected thiols and dithiols can be deprotected in situ
under acid or base conditions to form SAMs on gold substrate. The diazonium salt
generates an aryl radical by loss of N2 and ultimately produces an irreversible gold-
aryl bond. Isocyanide and diisocyanide also perform gold-carbon bond. Among all
the alligator clips, sulfur compounds have a strong affinity to transition metal
surfaces. This is probably because of the possibility to form multiple bonds with
surface metal clusters. The number of reported surface active organosulfur
compounds and their derivatives that form monolayers on gold include, di-n-alkyl
sulfide, di-n-alkyl disulfides, thiophenols, thiophenes, mercaptopyridines,
mercaptoanilines, xanthates, cysteines,thiocarbamates, thiocarbaminates, thioureas,
mercaptoimidazoles, ditellurides and alkaneselenols. SAMs of alkanethiolates on Au
surfaces are the most studied and well understood.

4.3 Electrode Effects

There has been great interest in molecular electronics since the observation of
electrical conductivity of the molecules from early experiments with the junction
formed by sandwiching the molecule between two metal electrodes. However, it has
been shown that in some systems, it was not the molecules themselves but the metal
contacts that mainly contribute to the junction conductivity. The misleading
observations from early experiments are due to the so called “metal nanofilaments”
effect. The “metal nanofilaments” effect is caused by the movements of metal atoms
from the contacts to the tiny gap (several nanometers) between the two contacts with
a bundle of molecules in between when an electric field is applied. The metal atoms
in the gap act as a low resistance bridge between the two contacts. Instead of flowing
through the molecule, electrical current tends to pass through the low-resistance
bridge. More recently, He et al. proposed a metal-free system in which the two sides
of a molecular monolayer attached to single-crystal silicon and a mat of single-
walled carbon nanotubes, respectively Figure .Such a design eliminated the metal
nanofilaments effect and switching property was observed under an applied field.
 (a) (b)
(a) Metal-molecule-metal junction with “metal nanofilaments” effect.
(b) Carbon nanotube-molecule-silicon junction.
Molecule-electrode interface is therefore a critically important component in
molecular electronics. It may limit the current flow or completely modify the
measured electrical response of the junction. Most experimental platforms for
constructing the molecular-electronic devices are based on the fact that the
sulfurgold bond is an excellent chemical handle for forming self-assembled, robust
organic monolayers on metal surfaces. Other methods, such as contacting a scanning
probe tip with the surface of the molecule, are frequently employed. Ideally, the
choice of electrode materials should not be based on the ease of fabrication or
measurement. They must follow the first-principles considerations of the molecule-
electrode interactions. However, the current level of understanding of the molecule-
electrode interface is rather poor. Very little theory exists that can adequately predict
how the energy levels of the molecular orbitals will align with the Fermi energy of

the electrode. Small changes in energy levels can dramatically affect the junction
conductance.

Therefore it is critical to understand the correlation of the interface energy levels

which demands both theoretical and experimental study. A relevant 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 molecule’s electronic structure
and the molecule-electrode interfaces. However, it is likely that the chemical
interaction between the molecule and the electrode will modify the molecule’s
electron density in the vicinity of the contacting atoms and, in turn, modify the
molecular energy levels or the barriers within the junction. There is little doubt that
the molecular and interface functions must be considered in tandem in theoretical
studies.

5. Applications of Molecular Electronics

Molecular electronics seeks to be the next technology in the electronics industry
where molecules assemble themselves into devices using environmentally friendly
and low cost fabrication techniques. It goes beyond the limitations of rigid silicon-
based solutions. It implements one or a few molecules to function as connections,
switches, and other logic devices in future computational devices. Molecular
electronics can be used in emerging technologies ranging from novel optical discs
based on bistable biomolecules to conceptual design of the computers based on
molecular switches and wires.

Molecular electronics seeks to be the next technology in the electronics industry

where molecules assemble themselves into devices using environmentally friendly
and low cost fabrication techniques. It goes beyond the limitations of rigid silicon-
based solutions. It implements one or a few molecules to function as connections,
switches, and other logic devices in future computational devices. Molecular
electronics can be used in emerging technologies ranging from novel optical discs
based on bistable biomolecules to conceptual design of the computers based on
molecular switches and wires. The processing speed of existing computers is limited
by the time it takes for an electron to travel between devices. Molecular electronics-
based computation addresses the ultimate requirements in a dimensionally scaled
system: ultra dense, ultra fast and molecular-scale. By the use of molecular scale
electronic interconnects, the transmittance times could be minimized. This could
result in novel computational systems operating at far greater speeds than
conventional inorganic electronics. The design of a molecular CPU can bring great
technical renovation in computer science. Table 1 shows the main differences
between the present bulk electronic devices and the proposed molecular electronic
devices.

Table 1:Main characteristics of bulk and molecular CPU circuits.

Novel molecular electronics would approach the density of ~10 13 logic gates/cm2. It
offers a 105 decrease in the size dimensions compared to the present feature of a
silicon-based microchip. In addition, the present fastest devices can only operate in
nanosecond while the response times of molecular-sized systems can reach the range
of femtoseconds. Thus, the speed may be attained to a 10 6 increase. On the basis of
these estimates, a 1011 fold increase in the performance can be expected with
molecular electronics, which offers an exciting impetus for intense research and
development though numerous obstacles remain.
Many of the technological applications of molecular electronics, including the
computational applications, should be considered and viewed as the drivers for the
field. Tour’s group has demonstrated the synthetic/computational approach to digital

computing of molecular scale electronics. In his paper, the alligator clip –SH acted as
the contact to input or output in digital computing of molecular electronics. The alkyl
groups which broke the conjugation of the wire served as the transport barrier in the
integrated circuits. The successful development of molecular-electronic integrated
circuitry would also benefit nanomechanical devices, ultradense single-molecule
sensor arrays, the interfaces to biosystems and the pathways toward molecular
mechanical systems.
5.1 Switch using Moletronics
Benzene ring of six carbon atoms (with a few hydrogen atoms thrown in as well) is
held together in part by a pi bond—a sort of smeared bond in which some of the
electrons are loosely shared by all the atoms in a kind of cloud that circles above and
below the carbon ring. It’s not a broken bond. Instead, it’s a sort of bond within
which electrons are somewhat more able to move.

By changing the structure of the molecule, the researchers found that they were able
to alter its behaviour. They hung molecular fragments—an NH2 group and an NO2
group—from the middle benzene ring. This distorted the electron cloud, making the
molecule more susceptible to twisting. By applying a voltage to the molecule, for
example, they could cause a “change, a bend or a twist in the molecule.” This
disrupted the flow of electrons
 And, this twist was reversible. When the voltage was removed, the molecule
returned to its original shape, allowing current to pass through once again. In other
words, this molecule can act as a switch. It turns electricity on and off—a basic
characteristic that a computer needs to process information in bits of 1 and 0.

5.2 Memory Chip

Data storage is done by multiporphyrin nanostructures into electronic memory. The
application of a voltage causes the molecules to oxidize, or give up electrons.The
molecules then retain their positive charge after the electric field is removed,
producing a memory effect.
5.2.1 Memory Hold Time
Silicon memory devices retain charged bits for only a millisecond before the charge
leaks away. That means that each piece of information must be restored ten to a
hundred times a second, which requires substantial amounts of power.

Moletronic device retains its electrons for about nearly fifteen minutes. It has the
ability to get the information in and out of the systems and using significantly less
power. Compared to, say, current equipment, which only runs for a few hours before
the batteries wear out, Reed says, machines using molecular memory could run for a
week.

There’s an energy structure that explains how long a device—either silicon, or

molecular—will hold electrons. They leak out at a certain rate and when you go to a
molecular structure, the energies [holding the electrons in place] become much
bigger. So the leak-out rate is slower.
6. Future of Molecular Electronics
The drive toward yet further miniaturization of silicon-based electronics has led to a
revival of efforts to build devices with molecular-scale organic components.
However, the fundamental challenges of realizing a true molecular electronics
technology are daunting. Controlled fabrication within specified tolerances and its
experimental verification are major issues. Self-assembly schemes based on
molecular recognition will be crucial for that task. Ability to measure electrical
properties of organic molecules more accurately and reliably is paramount in future
developments. Fully reproducible measurements of junction conductance are just
beginning to be realized in labs at Purdue, Harvard, Yale, Cornell, Delft, and
Karlsruhe Universities and at the Naval Research Laboratory and other centers.

Working molecular electronic devices exist today. Research progress is steady and
strong, giving us cause to believe that molecular electronic systems may be practical
in five to ten years. If lithography reaches fundamental physical or economic limits,
molecular electronics may allow us to continue observing Moore’s Law. Regardless,
molecular bottom-up fabrication could give us a
much better alternative, whose price would depend mainly on design and test cost,
instead of billion-dollar factories.

Challenges to making this reality are plentiful at every level, some naturally in
physics and chemistry, but many in ICCAD. These include fabricating and
integrating devices, managing their power and timing, finding fault-tolerant and
defect-tolerant circuits and architectures and the test algorithms needed to use them,
developing latency-tolerant circuits and systems, doing defect-aware placement and
routing, and designing, verifying and compiling billion-gate designs and the tools to
handle them. Any one of these could block practical molecular electronics if
unsolved.

Many of these are challenges that will be faced regardless of the underlying
technology. Molecular electronics provides a pure and extreme example, and
strengthens the case for solving them sooner rather than later.

Robust modeling methods are also necessary in order to bridge the gap between the
synthesis and understanding of molecules in solution and the performance of solid-
state molecular devices. In addition, the searching of fabrication approaches which
can couple the densities achievable through lithography with those achievable
through molecular assembly is also a great challenge. Controlling the properties of
molecule-electrode interfaces and constructing molecular-electronic devices that can
exhibit signal gain are also crucial to the development in the field.

7. REFERENCES

[1] Wikipedia

[2] Transcending Moore's Law with Molecular Electronics and Nanotechnology

http://www.dfj.com/files/TranscendingMoore.pdf
[3] STANFORD and HARVARD University thesis links.

[4] Hewlett-Packard Company Catalogue.

[5] Zettacore Company Catalogue.

[6] Elsevier Ltd link by Paula Gould.

[7] 2011 Molecular electronics archive

http://www.nature.com/nmat/archive/subject_nmatcode-13_012011.html

[8] YALE Engineering http://www.eng.yale.edu/posters150/pdf/reed4.pdf

[9] Other useful IEEE papers and links