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THE ROLE OF NANOTECHNOLOGY IN ELECTRONIC PROPERTIES OF

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Technical Report · June 2016

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THE ROLE OF

NANOTECHNOLOGY IN

ELECTRONIC PROPERTIES OF

MATERIALS

DR. Magy Mohamed Kandil

i

CONTENTS

Contents…………..…………………………..…………………………...……………………….....….i

Abstract …………..……………………………..………………………...……………………………..1 1.Introduction ……………………………………………………………………..…………………….1

1.1 Nanoscience And Nanotechnologies ……………………………………………………………….1

1.2 The Nanometre Scale…………………………….…………………………….……………………1

1.3 Quantum Effects & Nanomaterials Classification …………………………….………………….2

1.3.1 Zero-Dimensional Nanomaterials……………………………………...…………………………2

1.3.2 One-Dimensional Nanomaterials ………………………………………………...…...…………2

1.3.3 Two-Dimensional Nanomaterials……………………………………………...………………….3

1.3.3.1 Carbon Nanotubes…………………………….…………………………………………..…….3

1.3.4 Three-Dimensional Nanomaterials ……………………………………………..………….…….4

1.4 Approaches In Nanotechnology And Fabrication ………………………………………………….5

1.4.1 Top-Down Approach (Larger To Smaller: A Materials Perspective) …………………..……….5 1.4.2 Bottom-Up Approach (Simple To Complex: A Molecular Perspective) ….……….…………….5

1.5 Nano-Technology Types……………………………………………….………………….……….5

1.6 Instruments Used In Nanometrology …………………………………….……………….……….6

1.6.1 Electron Beam Techniques Transmission Electron Microscopy (Tem)… …………….………..6

1.6.2 Scanning Probe Techniques Scanning Probe Microscopy (Spm) ………………..…….………...6

1.6.3 Optical Tweezers (Single Beam Gradient Trap) ……………………….……………….…….….7

1.7 Historical Perspectives Of Nanoscience And Nanotechnology…………..………..……………....7

2 Electrical & Electronic Material Properties…………….…………………………….………….......9

2.1 Electrons In Solids Materials…………….…………………………………………………….......9

2.1.1 Insulators…………….…………………………………………..…………………….…….......9

2.1.2 In Semiconductors …………….……………………………………...........................................9

2.1.3 Conducting Materials …………….…………………………………………………….............10 2.2 Quantum Confinement And Its Effect On Material Electronic Properties…………….……..…11

2.2.1 Size Effect In Metal And Semiconductor …………….………………………………… …….11

2.3 Effects Of Nano Size In Electrical Properties …………….………………………..……… ……12

3 Nanomaterials Electronic Properties…………….…………………………...……………… ……12

3.1 Electronics…………….…………………………...……………………………………...…… ….12

3.2 Nanoelectronics…………….…………………………...……………… …………………...........13

3.3 Nanoelectronic Configuration …………….…………………………...………...………… …….13

3.4 Importance Of Nanostructures In Electronic …………….…………………………..……. ……14

3.5 The Electronic Behavior Of Materials At Nanoscale…………….…………....……….… ….…14

3.6 Nanomaterials Required Size For Size Effect…………….……………………………..… …….16

3.7 Nanoelectronics Technology …………….………………………...………...………… ………..17 3.7.1 Electrons Properties In Nanostructures………………………………………...…...…… …….17

3.8 Electrons In Nanostructures And Quantum Effects…………….…………………………...........18

3.9 Fermi Liquids And The Free Electron Model …………….………………………….…………..18

4. Electrons Nanostructures Application…………….…………………………...………...….. …….19

4.1 Nanoelectronic Devices…………….…………………………...………...……………..… ….…19

4.1.1 Nanoelectronic Transistors …………….…………………………...……..…...………… …....20

4.1.2 Memory Storage…………….…………………………...………...…………………...… ……21

4.2 Novel Optoelectronic Devices…………….…………………………...………...………… …….21

4.2.1 Displays…………….…………………………...………...……………………….……… ……22

4.2.2 Quantum Computers…………….…………………………...………...………….……… …….22

4.2.3 Radios…………….…………………………...………...…………………………...…… …….22

4.2.4 Energy Production…………….…………………………...…………………...………… …….23 4.2.5 Medical Diagnostics…………….…………………………...………………....………..… …..23

4.2.6 Nano-Robotics …………….…………………………...………........................………..…. ….23

4.2.7 Nanotechnology In Circuitry………….…………………………...………...……….....… …..23

4.2.8 Nano-Sensors………….…………………………...………...……………………….....… …..24

4.2.9 Multiplexers…………….…………………………...………...………………………..… …..24

5. Electronics And Computers…………….…………………………...………...……..……… …..24

5.1 Nanotechnology In Computer Processing…………….………………………...…..……… …..24

6. Nano Electronics: Applications under Development…………….……………………………..25

7. Emerging Applications of Radiation in Nanotechnology …………….…………………… ….27

8. Advantages and Disadvantages of using Nanotechnology…………..……………..…………..28

8.1 Advantages…………….…………………………...………...………………….……………..28

8.1.1 Energy Advantages…………….………………………….................……..…...………..….29

8.1.2 Advantages in Electronics and Computing…………….………………………....………....29 8.1.3 Medical Advantages………………………………………................…..……...……….….29

8.1.4 Environmental Effects…………………………….……….................…………...………... 29

8.1.5 Economic Upheaval…….………………………...……….....................………...……….....29

8.1.6 Privacy and Security…….………………………...……….....................………...……….. 30

8.1.7 Material Advantages …………….…………………………......………...……………… ....30

8.2 Disadvantages…………….………………………….................………...…………………....30

9. Conclusion …………….………………………….................………...…………………….. ....30

Reference …………….………………………….................………...………………………… ....32

1

ABSTRACT:

Nanotechnologies promise to be the foundation of the next industrial revolution. What

role can they play in electronic devices? This question has been raised, directly or

indirectly, by various authors and institutions since the year 2000, when

nanotechnology came to be the focus of government research programs, primarily in

the developed world but also in countries in the process of development. In this article

we review the positions taken by the principle institutions that addressed that question

in the period 2000-2016. We identify two main positions. One gives importance to

the technical advantages that nanotechnologies can offer to resolve key development

themes. The other position, which we call contextual, analyzes nanotechnologies

within the framework of the nanoelectronic in social, economic and political forces in

which they originate and are developed.

1. INTRODUCTION

1.1 Nanoscience and Nanotechnologies

Nanoscience is the study of phenomena and manipulation of materials at

atomic, molecular and macromolecular scales, where properties differ significantly

from those at a larger scale’ [1]. The application of nanoscience to ‘practical’ devices

is called nanotechnologies. Nanotechnologies are based on the manipulation, control

and integration of atoms and molecules to form materials, structures, components,

devices and systems at the nanoscale. Nanotechnologies are the application of

nanoscience especially to industrial and commercial objectives. All industrial sectors

rely on materials and devices made of atoms and molecules thus, in principle, all

materials can be improved with nanomaterials, and all industries can benefit from

nanotechnologies. In reality, as with any new technology, the ‘cost versus added

benefit’ relationship will determine the industrial sectors that will mostly benefit from

nanotechnologies. Thus, Nanotechnologies are the design, characterization,

production and application of structures, devices and systems by controlling shape

and size at the Nanometre scale.

Nanoscience deals with the scientific study of objects with sizes in the 1–100

nm range in at least one dimension. But Nanotechnology deals with using objects in

the same size range to develop products with possible practical application. It is

usually based on nanoscience insights. It is the creation of functional materials,

devices, and systems through control of matter on the nanometer length scale and the

exploitation of novel properties and phenomena developed at that scale. A scientific

and technical revolution has begun that is based upon the ability to systematically

organize and manipulate matter on the nanometer length scale[1].

1.2 The Nanometre scale

The Nanometre scale is conventionally defined as 1 to 100 nm. One

nanometre is one billionth of a metre (10-9 m). The size range is normally set to a

minimum of 1 nm to avoid single atoms or very small groups of atoms being

designated as nano-objects (Figure .1.). Therefore, nanoscience and nanotechnologies

deal with clusters of atoms of 1 nm in at least one dimension.’ Nanoscience is the

2

study of materials that exhibit remarkable properties, functionality and phenomena

due to the influence of small dimensions.

Figure .1. A nanomaterial is an object that has at least one dimension in the nanometre

scale (approximately 1 to 100 nm).

1.3 Quantum mechanics (QM) & Nanomaterials Classification

Quantum mechanics (QM); also known as quantum physics or quantum

theory), including quantum field theory, is a fundamental branch of physics concerned

with processes involving, for example, atoms and photons. In such processes, said to

be quantized, the action has been observed to be only in integer multiples of

the Planck constant. This is utterly inexplicable in classical physics. Quantum

mechanics gradually arose from Max Planck's solution in 1900 to the black-body

radiation problem (reported 1859) and Albert Einstein's 1905 paper which offered a

quantum-based theory to explain the photoelectric effect (reported 1887). Early

quantum theory was profoundly reconceived in the mid-1920s.

The reconceived theory is formulated in various specially developed

mathematical formalisms. In one of them, a mathematical function, the wave function,

provides information about the probability amplitude of position, momentum, and

other physical properties of a particle. Important applications of quantum mechanical

theory include superconducting magnets, light-emitting diodes and the laser, the

transistor and semiconductors such as the microprocessor, medical and research

imaging such as magnetic resonance imaging and electron microscopy, and

explanations for many biological and physical phenomena.

Bulk materials (the ‘big’ pieces of materials we see around us) possess

continuous (macroscopic) physical properties. The same applies to micron-sized

materials (e.g. a grain of sand). But when particles assume nanoscale dimensions, the

principles of classic physics are no longer capable of describing their behaviour

(movement, energy, etc.): at these dimensions, the principles of quantum mechanics

principles. The same material (e.g. gold) at the nanoscale can have properties (e.g.

optical, mechanical and electrical) which are very different from (and even opposite

to!) the properties the material has at the macroscale (bulk).

The overall behavior of bulk crystalline materials changes when the

dimensions are reduced to the nanoscale. For 0-D Nanomaterials, where all the

3

dimensions are at the nanoscale, an electron is confined in 3-D space. No electron

delocalization (freedom to move) occurs. For 1-D Nanomaterials, electron

confinement occurs in 2-D. For 1-D Nanomaterials, electron confinement occurs in

2-D, whereas delocalization takes place along the long axis of the nanowire/rod/tube.

In the case of 2-D Nanomaterials, the conduction electrons will be confined across the

thickness but delocalized in the plane of the sheet. Nanomaterials Classification is

based on the number of dimensions, which are not confined to the nanoscale range as

shown in figure .2.

1.3.1 Zero-dimensional Nanomaterials

Materials wherein all the dimensions are measured within the nanoscale (no

dimensions, or 0-D, are larger than 100 nm). The most common representation of

zero-dimensional nanomaterials are nanoparticles. Nanoparticles can: be amorphous

or crystalline; be single crystalline or polycrystalline; be composed of single or

multi-chemical elements; exhibit various shapes and forms; exist individually or

incorporated in a matrix and be metallic, ceramic, or polymeric.[2]

1.3.2 One-dimensional Nanomaterials

One dimension that is outside the nanoscale. This leads to needle like-shaped

Nanomaterials. 1-D materials include nanotubes, nanorods, and nanowires. In 1-D

Nanomaterials nanomaterials can be Amorphous or crystalline; Single crystalline or

polycrystalline; Chemically pure or impure Standalone materials or embedded in

within another medium Metallic, ceramic, or polymeric.

1.3.3 Two-dimensional Nanomaterials

Two of the dimensions are not confined to the nanoscale. 2-D nanomaterials

exhibit plate-like shapes. Two-dimensional nanomaterials include nanofilms,

nanolayers, and nanocoatings. 2-D nanomaterials nanomaterials can be: can be:

amorphous or crystalline made up of various chemical compositions used as a single

layer or as multilayer structures; Deposited on a substrate and integrated in a

surrounding matrix material metallic, ceramic, or polymeric.

Two dimensional Nanomaterials such as tubes and wires have generated

considerable interest among the scientific community in recent years. In particular,

their novel electrical and mechanical properties are the subject of intense research.

1.3.3.1 Carbon Nanotubes

Carbon nanotubes (CNTs) were first observed by Sumio Iijima in 1991. CNTs

are extended tubes of rolled graphene sheets. There are two types of CNT: single-

walled (one tube) or multi-walled (several concentric tubes). Both of these are

typically a few nanometres in diameter and several micrometres to centimetres long.

CNTs have assumed an important role in the context of nanomaterials, because of

their novel chemical and physical properties. They are mechanically very strong

(their Young’s modulus is over 1 terapascal, making CNTs as stiff as diamond),

flexible (about their axis), and can conduct electricity extremely well (the helicity of

the graphene sheet determines whether the CNT is a semiconductor or metallic). All

4

of these remarkable properties give CNTs a range of potential applications: for

example, in reinforced composites, sensors, nanoelectronics and display devices [3].

1.3.4 Three-dimensional Nanomaterials

Bulk nanomaterials are materials that are not confined to the nanoscale in any

dimension. These materials are thus characterized by having three arbitrarily

dimensions above 100 nm. Materials possess a nanocrystalline structure or involve

the presence of features at the nanoscale. In terms of nanocrystalline structure, bulk

nanomaterials can be composed of a multiple arrangement of nanosize crystals, most

typically in different orientations. With respect to the presence of features at the

nanoscale, 3-D nanomaterials can contain dispersions of nanoparticles, bundles of

nanowires, and nanotubes as well as multinanolayers.

Figure .2. Nanomaterials Classification

Figure .3. The relationships among Nanomaterials Classification

0- among 0-D, 1-D, 2-D, and 3-D

As shown in figures 2 & 3, Nanostructures refer to materials systems with

length scale in the range of ~ 1-100 nm in at least one dimension. In a nanostructure,

electrons are confined in the nanoscale dimension(s), but are free to move in other

5

dimension(s). One way to classify nanostructures is based on the dimensions in

which electrons move freely:

Quantum well: electrons are confined in one dimension (1D), free in other 2D. It can

be realized by sandwiching a narrow-bandgap semiconductor layer between the wide-

gap ones. A quantum well is often called a 2D electronic system.

Quantum wires: confined in two dimensions, free in 1D (so it is called a 1D

electronic system). Real quantum wires include polymer chains, nanowires and

nanotubes.

Quantum dots: electrons are confined in all dimensions, as in clusters and

nanocrystallites [5]

Nanostructured materials consist of many forms such as:

• Nanoparticles

• Nanowires

• Nanotubes

• Nanorods

• Nanoporous materials

• Other structures

1.4 Approaches in nanotechnology and Fabrication

1.4.1 Top-down Approach (Larger to smaller: a materials perspective)

Creating Nano-scale materials by physically or chemically breaking down

larger materials. A number of physical phenomena become pronounced as the size of

the system decreases. These include statistical mechanical effects, as well as quantum

mechanical effects.

Solid-state techniques can also be used to create devices known as

nanoelectromechanical systems or NEMS, which are related to

microelctromechanical systems or MEMS. MEMS became practical once they could

be fabricated using modified semiconductor device fabrication technologies, normally

used to make electronics [6].

1.4.2 Bottom-up Approach (Simple to complex: a molecular perspective)

Modern synthetic chemistry has reached the point where it is possible to

prepare small molecules to almost any structure. These methods are used today to

manufacture a wide variety of useful chemicals such as pharmaceuticals or

commercial polymers. Molecular nanotechnology, sometimes called molecular

manufacturing, describes engineered nanosystems (nanoscale machines) operating on

the molecular scale. Molecular nanotechnology is especially associated with the

molecular assembler, a machine that can produce a desired structure or device atom-

by-atom using the principles of mechanosynthesis [7].

1.5 Nano-technology Types

Nanotechnology is ubiquitous and pervasive. It is and emerging field in all

areas of science, engineering and technology. Some are as given.

• Nano-Material.

• Nano-Electronic.

6

• Nano-Robotics.

• Molecular mechanics Nano engineering

• Nanobiotechnology

• Nanofluidics

• Nanohub

• Nanometrology

• Nanoscale networks

1.6 Instruments used in nanometrology

1.6.1 Electron beam techniques Transmission electron microscopy (TEM)

It is used to investigate the internal structure of micro- and nanostructures. It

works by passing electrons through the sample and using magnetic lenses to focus the

image of the structure, much like light is transmitted through materials in

conventional light microscopes. Because the wavelength of the electrons is much

shorter than that of light, much higher spatial resolution is attainable for TEM images

than for a light microscope. TEM can reveal the finest details of internal structure, in

some cases individual atoms. The samples used for TEM must be very thin (usually

less than 100nm), so that many electrons can be transmitted across the specimen.

However, some materials, such as nanotubes, nanocrystalline powders or small

clusters, can be directly analysed by deposition on a TEM grid with a carbon support

film. TEM and high-resolution transmission electron microscopy (HRTEM) are

among the most important tools used to image the internal structure of a sample.

Furthermore, if the HRTEM is adequately equipped, chemical analysis can be

performed by exploiting the interactions of the electrons with the atoms in the sample.

The scanning electron microscope (SEM) uses many of the basic technology

developed for the TEM to provide images of surface features associated with a

sample. Here, a beam of electrons is focused to a diameter spot of approximately 1nm

in diameter on the surface of the specimen and scanned back and forth across the

surface.

The surface topography of a specimen is revealed either by the reflected

(backscattered) electrons generated or by electrons ejected from the specimen as the

incident electrons decelerate secondary electrons. A visual image, corresponding to

the signal produced by the interaction between the beam spot and the specimen at

each point along each scan line, is simultaneously built up on the face of a cathode ray

tube similar to the way that a television picture is generated. The best spatial

resolution currently achieved is of the order of 1nm [8].

1.6.2 Scanning probe techniques Scanning probe microscopy (SPM)

It uses the interaction between a sharp tip and a surface to obtain an image.

The sharp tip is held very close to the surface to be examined and is scanned back-

and-forth. The scanning tunnelling microscope (STM) was invented in 1981 by Gerd

Binnig and Heinrich Rohrer, who went on to collect the Nobel Prize for Physics in

1986. Here, a sharp conducting tip is held sufficiently close to a surface (typically

about 0.5nm) that electrons can ‘tunnel’ across the gap. The method provides surface

structural and electronic information with atomic resolution. The invention of the

STM led directly to the development of other ‘scanning probe’ microscopes, such as

the atomic force microscope.

7

The atomic force microscope (AFM) uses a sharp tip on the end of a flexible

beam or cantilever. As the tip is scanned across the sample, the displacement of the

end of the cantilever is measured, usually a laser beam. Unlike the STM, where the

sample has to be conductive, an AFM can image insulating materials simply because

the signal corresponds to the force between the tip and sample, which reflects the

topography being scanned across. There are several different modes for AFM. In

contact mode, the tip touches the sample; this is simple to implement but can lead to

sample damage from the dragging tip on soft materials. Tapping mode mitigates this

difficulty: the tip is oscillated and only touches intermittently, so that dragging during

scanning is minimized. Non-contact mode is where the tip senses only the attractive

forces with the surface, and causes no damage. It is technically more difficult to

implement since these forces are weak compared with contact forces. In non-contact

mode at larger tip-surface separation, the imaging resolution is poor, and the

technique not often used. However, at small separation, which requires specialized

AFM apparatus to maintain, true atomic resolution can be achieved in non-contact

mode AFM.

1.6.3 Optical tweezers (single beam gradient trap)

Optical tweezers use a single laser beam (focused by a high-quality

microscope objective) to a spot on a specimen plane. The radiation pressure and

gradient forces from the spot creates an ‘optical trap’ which is able to hold a particle

at its centre. Small interatomic forces and displacements can then be measured.

Samples that can analyzed range from single atoms and micrometre-sized spheres to

strand of DNA and living cells. Optical tweezers are now a standard method of

manipulation and measurement. Numerous traps can be used simultaneously with

other optical techniques, such as laser scalpels, which can cut the particle being

studied [9].

1.7 Historical perspectives of Nanoscience and Nanotechnology

Richard Feynman’s 1959 lecture “There is plenty of room at the bottom” has

often been quoted when people talk about nanoscience and nanotechnology. He

predicted that “we will get an enormously greater range of properties that substances

can have, and of different things that we can do” if atoms and molecules can be

arranged in the way we want. However, the real take-off of nano-related research and

technological exploitation started at about 15 years ago. This is a logical consequence

of the developments of science and technology.

The Japanese scientist called Norio Taniguchi of the Tokyo University of

Science was the first to use the term "nano-technology" in a 1974 conference,[7]

to

describe semiconductor processes such as thin film deposition and ion beam milling

exhibiting characteristic control on the order of a nanometer. His definition was,

"'Nano-technology' mainly consists of the processing of, separation, consolidation,

and deformation of materials by one atom or one molecule." However, the term was

not used again until 1980 when Eric Drexler, who was unaware of Taniguchi's prior

use of the term, published his first paper on nanotechnology in 1980.

In the 1980s the idea of nanotechnology as a deterministic, rather than stochastic,

handling of individual atoms and molecules was conceptually explored in depth by K.

Eric Drexler, who promoted the technological significance of nano-scale phenomena

and devices through speeches and two influential books. In 1980, Drexler encountered

8

Feynman's provocative 1959 talk "There's Plenty of Room at the Bottom" while

preparing his initial scientific paper on the subject, “Molecular Engineering: An

approach to the development of general capabilities for molecular manipulation,”

published in the Proceedings of the National Academy of Sciences in 1981.[1] The

term "nanotechnology" (which paralleled Taniguchi's "nano-technology") was

independently applied by Drexler in his 1986 book Engines of Creation: The Coming

Era of Nanotechnology, which proposed the idea of a nanoscale "assembler" which

would be able to build a copy of itself and of other items of arbitrary complexity. He

also first published the term "grey goo" to describe what might happen if a

hypothetical self-replicating machine, capable of independent operation, were

constructed and released. Drexler's vision of nanotechnology is often called

"Molecular Nanotechnology" (MNT) or "molecular manufacturing." .His 1991 Ph.D.

work at the MIT Media Lab was the first doctoral degree on the topic of molecular

nanotechnology and (after some editing) his thesis, "Molecular Machinery and

Manufacturing with Applications to Computation," [11] was published

as Nanosystems: Molecular Machinery, Manufacturing, and Computation,[12]

which

received the Association of American Publishers award for Best Computer Science

Book of 1992. Drexler founded the Foresight Institute in 1986 with the mission of

"Preparing for nanotechnology.” Drexler is no longer a member of the Foresight

Institute [10].

The 20th Century has been called the Century of Physics because of the

revolutionary development of physics and its tremendous impacts. A solid foundation

has been laid to describe the Nature at the elementary particle level at one end to the

evolution of the Universe at the other. Of close relevance to our life (and economy),

quantum mechanics has helped us to reveal the nature of atoms, molecules and solids.

Solid state physics led to the creation and great success of semiconductor science and

engineering. Integrated circuits, laser and magnetic disks are indispensable to the

Information Technology and our daily life.

Our understanding and exploitation of electronic configuration material world around

us have been pushing forward in two opposite directions: from the bottom up and

from the top down. In the bottom-up approach, we start with electrons and nucleons

as the building blocks. The properties of atoms and most of relatively simple

molecules (this can be called the sub-nm world) have been well understood. At

increasing complexity levels, we are dealing with macro-molecules, polymers,

clusters and bio-molecules (These are relatively small nanostructures we will deal

with). On the other hand, we have been reducing the sizes of solid state devices (e.g.,

transistors, date storage bits) from macroscopic scales to deep sub-micron (~ 0.1-0.2

m), as shown in the 1999 International Technology Roadmap for Semiconductors

(ITRS) in Table 1, and into deep sub-0.1-m scale in ten years. So far, the physical

principle of device operation has not changed dramatically in the scaling-down

process. But this will not likely be the case for the next decade [11].

9

The top-down and bottom-up approaches have largely developed

independently in the past. Today, these two meet at the nanoscale territory. This

means that people along the top-down line have to consider the behavior of nature at

the atomic scales, while those taking the bottom-up approach are ready to fabricate

novel devices and materials with numerable atoms and molecules as the building

blocks. More importantly, these atomic or molecular devices will not just be toys

played by researchers for fun or writing academic papers and thesis, but really work

with indispensable functions in our PCs, mobile phones, cars, home appliances, and in

health products and services. Nanoscience and nanotechnology should not be

considered as a fashionable hot subject. Rather, they are a logic development stage of

research and development that is built on previous achievements [12]

2 ELECTRICAL & ELECTRONIC MATERIAL PROPERTIES

There are three categories of materials based on their electrical properties: (a)

conductors; (b) semiconductors; and (c) insulators. The energy separation between the

valence band and the conduction band is called Eg (band gap). The ability to fill the

conduction band with electrons and the energy of the band gap determine whether a

material is a conductor, a semiconductor or an insulator.

2.1 Electrons in solids materials

2.1.1 Insulators

Core shell electrons are tightly bound to atoms, and do not interact strongly

with electrons in other atoms, Valence shell electrons are the outer electrons that

contribute to bonds between atoms core valence conduction Electron energy. If all of

the bonds are “satisfied” by valence electrons, and if these bonds are strong, then the

material does not conduct electricity - an insulator as shown in figure .4.

Figure 4 Electronic configuration in Insulators

As shown in figure 4 Insulators have large bandgaps that require an enormous

amount of voltage to overcome the threshold. This is why these materials do not

conduct electricity [13].

2.1.2 In semiconductors

If all the bonds are “satisfied”, but the bonds are relatively weak, then the

material is an intrinsic semiconductor, and thermal energy can break a small number

of bonds, releasing the electrons to conduct electricity as shown in figure .5.

10

Figure .5. Electronic configuration in an intrinsic semiconductor

If impurities with one more or one fewer electrons than a host atom are

substituted for host atoms in a semiconductor, then the material becomes conductive -

an extrinsic semiconductor as shown in figure .6.

Figure .6. Electronic configuration in an extrinsic semiconductor

As shown in figures 5 &6 , in semiconductors, the band gap is a few electron

volts. If an applied voltage exceeds the band gap energy, electrons jump from the

valence band to the conduction band, thereby forming electron-hole pairs called

exactions.

2.1.3 Conducting materials

If only a fraction of the bonds are satisfied (or alternatively, if there are many

more electrons than are needed for bonding) then there is a high density of electrons

that contribute to conduction, and the solid is a metal as shown in figure .7.

Figure .7. Electronic configuration in conducting materials

As shown in figure .7, in conducting materials like metals, the valence band

and the conducting band overlap, so the value of Eg is small: thermal energy is

enough to stimulate electrons to move to the conduction band.

If only a fraction of the bonds are satisfied (or alternatively, if there are many more

electrons than are needed for bonding) then there is a high density of electrons that

contribute to conduction, and the solid is a metal

11

2.2 Quantum confinement and its effect on material Electronic properties

As shown in section 1.3, in Nano crystals, the electron energy levels are not

continuous as in the bulk but are discrete (finite density of states) because of the

confinement of the electron wave function to the physically dimensions of the

particles. This phenomenon is called Quantum confinement and therefore Nano

crystals are also referred to Quantum dots.

Quantum confinement causes the energy of the band gap to increase as illustrated in

Figure .8. Furthermore, at very small dimensions when the energy levels are

quantified, the band overlap present in metals disappears and is actually transformed

into a band gap. This explains why some metals become semiconductors as their size

is decreased [14].

Figure.8. The image compares the energy of the band gap (arrow) in a bulk semiconductor, a quantum dot and an atom. As more energy states are lost due to the shrinking size, the energy

band gap increases.

The increase in band gap energy due to quantum confinement means that more

energy will be needed in order to be absorbed by the band gap of the material. Higher

energy means shorter wavelength (blue shift). The same applies to the wavelength of

the fluorescent light emitted from the nano-sized material, which will be higher, so

the same blue shift will occur. Thus, a method of tuning the optical absorption and

emission properties of a nano-sized semiconductor over a range of wavelengths by

controlling its crystallite size is provided. The optical properties of nano-sized metals

and semiconductors (quantum dots).

Nanomaterials with exceptional electrical properties Some nanomaterials

exhibit electrical properties that are absolutely exceptional. Their electrical properties

are related to their unique structure. Two of these are fullerenes and carbon

nanotubes. For instance, carbon nanotubes can be conductors or semiconductors

depending on their nanostructure. Another example is that of supercapacitors

materials in which there is effectively no resistance and which do not obey Ohm’s law

[15].

2.2.1 Size effect in metal and semiconductor

In any material, there will be a size below which there is substantial variation

of fundamental electrical and optical properties with size, when energy level spacing

exceeds the temperature. For a given temperature, this occurs at a very large size (in

nanometers) in semiconductors as compared with metals and insulators. The quantum

size effect is most pronounced for semiconductor nanoparticles, where the band gap

increases with a decreasing size, resulting in the interband transition shifting to higher

frequencies.

12

2.3 Effects of Nano size in electrical properties

Properties depends on size, composition and structure:

• Nano size increases the surface area

• Change in surface energy (higher)

• Change in the electronic properties

• Change in optical band gap

• Change in electrical conductivity

• Higher and specific catalytic activity

• Change thermal and mechanical stabilities

• Different melting and phase transition temperatures

• Change in catalytic and chemical reactivities

3 NANOMATERIALS ELECTRONIC PROPERTIES

3.1 Electronics

Electronics is the science of how to control electric energy, energy in which

the electrons have a fundamental role. Electronics deals with electrical circuits that

involve active electrical components such as vacuum

tubes, transistors, diodes and integrated circuits, and associated passive electrical

components and interconnection technologies. Commonly, electronic devices contain

circuitry consisting primarily or exclusively of active semiconductors supplemented

with passive elements; such a circuit is described as an electronic circuit.

The nonlinear behaviour of active components and their ability to control

electron flows makes amplification of weak signals possible, and electronics is widely

used in information processing, telecommunication, and signal processing. The ability

of electronic devices to act as switches makes digital information processing possible.

Interconnection technologies such as circuit boards, electronics packaging technology,

and other varied forms of communication infrastructure complete circuit functionality

and transform the mixed components into a regular working system.

Electronics is distinct from electrical and electro-mechanical science and

technology, which deal with the generation, distribution, switching, storage, and

conversion of electrical energy to and from other energy forms

using wires, motors, generators, batteries, switches, relays, transformers, resistors, and

other passive components. This distinction started around 1906 with the invention

by Lee De Forest of the triode, which made electrical amplification of weak radio

signals and audio signals possible with a non-mechanical device. Until 1950 this field

was called "radio technology" because its principal application was the design and

theory of radio transmitters, receivers, and vacuum tubes.

Today, most electronic devices use semiconductor components to perform

electron control. The study of semiconductor devices and related technology is

considered a branch of solid-state physics, whereas the design and construction of

electronic circuits to solve practical problems come under electronics engineering.

This article focuses on engineering aspects of nano electronics [16].

13

3.2 Nanoelectronics

Nanoelectronics are part of the nanotechnology domain, which deals with the

characterization, manipulation and fabrication of the electronic devices at the

nanoscale. Nanoelectronics is one of the major technologies of Nanotechnology. It

plays vital role in the field of engineering and electronics. Nanoelectronics make use

of scientific methods at atomic scale for developing the Nano machines. The main

target is to reduce the size, risk factor and surface areas of the materials and

molecules. Machines under nano electronic process undergoes the long range of

manufacturing steps each with accurate molecular treatment. This article focuses

on engineering aspects of Nanoelectronics.

The Nanotechnology field has been the subject of intense focus, particularly

from the viewpoint of the electronics industry. The commitment is, no doubt, driven

to a large measure by the current top-down methodologies for fabrication of silicon-

based devices. This is implied in the next-generation approach towards manufacture

of MEMS, microprocessors, optical switching and several other electronic

components. Nanoelectronic devices; are a very small devices to overcome limits on

scalability

Nanotechnology is continually playing vital role to improve the capability of

electronic products. The technology also made the devices very light making the

product easy to carry or move and at the same time it has reduced the power

requirement. Some Consumer Products which are using Nanotechnology:

Computer Hardware

Display Devices

Mobile & Communication Products

Audio Products

Camera & Films

The world market for nanoelectronics is expected to reach $409.6 billion by

2017 [17].

3.3 Nanoelectronic configuration

The electronic configurations of Nanomaterials are significantly different from

that of their bulk counterpart. These changes arise through systematic transformations

in the density of electronic energy levels (Density of states (DOS)) as a function of

the size, and these changes result in strong variations in the optical and electrical.

While the DOS in a band could be very large for some materials, it may not be

uniform. It approaches zero at the band boundaries, and is generally higher near the

middle of a band. The density of states for the free electron model. In statistical and

condensed matter physics, the density of states (DOS) of a system describes the

number of states at each energy level that are available to be occupied. A high DOS at

a specific energy level means that there are many states available for occupation. A

DOS of zero - no states can be occupied at that energy level. near the middle of a

band. The density of states for the free electron model in three dimensions is shown

by figure .9.

14

Figure .9. Density of states for 3D, 2D, 1D, 0D

showing discretization of energy and discontinuity of DOS

3.4 Importance of Nanostructures in Electronic

Nanotechnology is already being used by the electronic industry and you will

be surprised to know that many of today’s electronics have already incorporated many

applications that the nanotechnology science has developed. For example, new

computer microprocessors have less than 100 nanometers (nm) features. Smaller sizes

mean a significant increase in speed and more processing capability [18].

These advances will undoubtedly help achieve better computers. However, at

some point in time (very near in the future) current electronic technology will no

longer be enough to handle the demand for new chips microprocessors. Right now,

the method for chip manufacturing is known as lithography or etching. By this

technology, a probe literally writes over a surface the chip circuit. This way of

building circuits in electronic chips has a limitation of around 22 nanometers (most

advanced chip processors uses 60-70 nm size features). Below 22 nm errors will occur

and short circuits and silicon limitations will prevent chip manufacturing.

3.5 The Electronic behavior of Materials at Nanoscale

Materials behave electronic differently at Nanoscale for two reasons: Firstly,

very small particles have a larger surface area compared to the same amount of

material in a larger lump (for example, grains of sand would cover a bigger surface

than the same amount of sand compressed into a stone). As the surface of the particle

is involved in chemical reactions, the larger surface area can make materials more

reactive – grains of salt dissolve in water much more quickly than a rock of salt for

example. In fact, some materials that are generally inactive in their larger form can be

more reactive in nanoscale. Secondly, when we look at materials on a nanoscale

level, the relative importance of the different laws of physics shift and effects that we

normally do not notice (such as quantum effects) become more significant, especially

for sizes less than 20nm.

This is mainly due to the nanometer size of the materials which render them:

1. large fraction of surface atoms;

2. high surface energy;

3. spatial confinement;

4. reduced imperfections, which do not exist in the corresponding bulk materials.

Nanostructures are unique as compared with both individual atoms/molecules

at a smaller scale and the macroscopic bulk materials. They are also called

mesoscopic structures. Nanoscience research focuses on the unique properties of

15

nanoscale structures and materials that do not exist (or only very weakly exist) in

structures of same material composition but at other scale ranges.

In Electronic, the wave like properties of electrons inside matter are influenced by

variations on the nanometer scale. By patterning matter on the nanometer length, it is

possible to vary fundamental properties of materials (for instance, melting

temperature, magnetization, charge capacity) without changing the chemical

composition. The systematic organization of matter on the nanometer length scale is

a key feature of biological systems. Nanotechnology promises to allow us to place

artificial components and assemblies inside cells, and to make new materials using the

self-assembly methods of nature.

Nanostructures components have very high surface areas, making them ideal

for use in composite materials, reacting systems, drug delivery, and energy storage.

The finite size of material entities, as compared to the molecular scale, determine an

increase of the relative importance of surface tension and local electromagnetic

effects, making Nanostructured materials harder and less brittle. The interaction

wavelength scales of various external wave phenomena become comparable to the

material entity size, making materials suitable for various opto-electronic

applications. Nano-materials: Used by humans for 100 of years, the beautiful ruby

red color of some glass is due to gold Nano particles trapped in the glass (ceramic)

matrix[19].

There are various reasons why nanoscience and nanotechnologies are so

promising in electronic properties of materials and engineering. First, at the

nanometre scale, the electronic properties of matter, such as energy, change. This is a

direct consequence of the small size of Nanomaterials, physically explained as

quantum effects. The consequence is that a material (e.g. a metal) when in a nano-

sized form can assume properties which are very different from those when the same

material is in a bulk form. For instance, bulk silver is non-toxic, whereas silver

nanoparticles are capable of killing viruses upon contact. Properties like electrical

conductivity, colour, strength and weight change when the nanoscale level is reached:

the same metal can become a semiconductor or an insulator at the nanoscale level.

The second exceptional property of nanomaterials is that they can be fabricated atom

by atom by a process called bottomup. The information for this fabrication process is

embedded in the material building blocks so that these can self-assemble in the final

product [20].

Bulk materials (e.g., a Cu wire, a cup of water), their intrinsic physical

properties, such as density, conductivity and chemical reactivity, are independent of

their sizes. For example, if a one-meter Cu wire is cut into a few pieces, those

intrinsic properties of the shorter wires remain the same as in the original wire. If the

dividing process is repeated again and again, this invariance cannot be kept

indefinitely. Certainly, we know that the properties are changed greatly when the

wire is divided into individual Cu atoms (even more at the level of electrons, protons

and neutrons). Significant property changes often start when we get down to the

nanoscales. The following phenomena critically affect the properties of nanostructural

materials:

1. Quantum confinement: the confinement of electrons in the nanoscale dimensions

result in quantization of energy and momentum, and reduced dimensionality of

electronic states

2. Quantum coherence: certain phase relation of wave function is preserved for

electrons moving in a nanostructure, so wave interference effect must be considered.

But in nanostructures, generally the quantum coherence is not maintained perfectly as

16

in atoms and molecules. The coherence is often disrupted to some extent by defects

in the nanostructures. Therefore, both quantum coherent and de-coherent effects have

to be considered, which often makes the description of electronic motion in a

nanostructure more complicated than in the extreme cases.

3. Surface/interface effects: a significant fraction (even the majority) of atoms in

nanostructure is located at and near the surfaces or interfaces. The mechanic,

thermodynamic, electronic, magnetic, optical and chemical states of these atoms can

be quite different than those interior atoms.

These factors play roles to various degrees (but not 100%) of importance. For

example, the confinement and the coherent effects are not as complete as that in an

atom. Both the crystalline (bulk) states and the surface/interface states cannot be

ignored in nanoscale structures. The different mixture of atomic/molecular,

mesoscopic and macroscopic characters make the properties of nanostructures vary

dramatically. Nanostructural materials are often in a metastable state. Their detailed

atomic configuration depends sensitively on the kinetic processes in which they are

fabricated. Therefore, the properties of nanostructures can be widely adjustable by

changing their size, shape and processing conditions. The situation is similar to

molecular behavior in chemistry (e.g., N vs. N2) in certain aspect. Because of the rich

and often surprising outcomes, it will be extremely interesting and challenging to play

with nanostructural systems. Nanoscience and nano-engineering have been an area

where many breakthroughs have been and will continue to be produced [21].

3.6 Nanomaterials Required size for size effect

As shown in section 2.1, in the case of metals, where the Fermi level lies in

the centre of a band and the relevant energy level spacing is very small, the electronic

and optical properties more closely resemble those of continuum, even in relatively

small sizes (tens or hundreds of atoms). In semiconductors, the Fermi level lies

between two bands, so that the edges of the bands are dominating the low-energy

optical and electrical behavior. Optical excitations across the gap depend strongly on

the size, even for crystallites as large as 10,000 atoms.

For insulators, the band gap between two bands is already too big in the bulk form.

The same quantum size effect is also known for metal nanoparticles; however, in

order to observe the localization of the energy levels, the size must be well below 2

nm, as the level spacing has to exceed the thermal energy (~26 meV). In a metal, the

conduction band is half filled and the density of energy levels is so high that a

noticeable separation in energy levels within the conduction band (intraband

transition) is only observed when the nanoparticle is made up of ~100 atoms. If the

size of metal nanoparticle is made small enough, the continuous density of electronic

states is broken up into discrete energy levels. The spacing δ , between energy levels

depends on the Fermi energy of the metal EF, and on the number of electrons in the

metal, N, as given by:

(1)

Where: the Fermi energy EF is typically of the order of 5 eV in most metals. For

example; the discrete electronic energy level in metal nanoparticles has been observed

in far-infrared absorption measurements of gold nanoparticle. When the diameter of

nanowires or nanorods reduces below the de Broglie wavelength, size confinement

would also play an important role in determining the energy level just as for

17

nanocrystals. For example, the absorption edge of Si nanowires has a significant blue

shift with sharp, discrete features and silicon nanowires also have shown relatively

strong "band-edge" photoluminescence [22].

3.7 Nanoelectronics Technology

Nanoelectronics technology deals with the characterization, manipulation and

fabrication of the electronic devices at the nanoscale. But, Nanoelectronic device is a

very small devices to overcome limits on scalability. Nanoelectronics holds some

answers for how we might increase the capabilities of electronics devices while we

reduce their weight and power consumption.

3.7.1 Electrons properties in Nanostructures

The electronic properties of materials change when electrons are confined to

structures that are smaller than the distance between scattering events (i.e., the mean

free path) of electrons in normal solids. In this section, we will discuss what happens

to electrons that are confined to one-dimensional structures (i.e., constrictions or

“wires”) and zero-dimensional structures (i.e., small particles). Two-dimensional

confinement will be dealt with in semiconductor heterostructures in As a prerequisite

for this material, we begin with a broad overview of conduction in normal solids,

including the “free electron” model of metals and the band structure theory of the

electronic states in periodic solids [23].

The vast variation in the electronic properties of materials The electrical

properties of materials vary vastly. We think of electrical properties in terms of

resistance: the copper wires that carry electrical power have a low resistance and the

glass insulators that support power lines have a very high resistance. Resistance

depends on geometry and a more intrinsic quantity is resistivity, ρ. For example, a rod

of material of length, L, and cross-sectional area, A, has a resistance

R = ρL A (2)

ρ is purely a material property, having units of Ω -m.

The resitivities of some common materials are shown in Table .1. (The units

here are Ω-m, but Ω - cm are more commonly used in the semiconductor industry.)

Few physical quantities vary as much as resitivity: the range between copper and

rubber is nearly 24 orders of magnitude! Only a fraction of the electrons in a given

material are involved in conducting electricity. For example, only one of the 29

electrons in each copper atom in a copper wire is free to carry a current. We shall see

that these electrons move very quickly – about 106 m/s. However, they are also

scattered very frequently – on average about every 40 nm in copper. The net current is

carried by a slow drift of this randomly scattered cloud of electrons.

The drift velocity depends upon the voltage drop across the copper wire, but for the

small voltages dropped across typical appliance leads (a fraction of a volt per meter at

high current) it is a fraction of a mm per second. Despite the fact that they are in a

minority, these “free electrons” give metals remarkable properties. In addition to their

ability to pass electric currents, incident optical fields set free electrons into a motion

that opposes the incident field, reradiating the light as a reflection, accounting for the

optical reflectivity of most metals. Most of the elements in the periodic table are

18

metals, with only those few on or to the right of the diagonal B-Si-As-Te-At being

semiconductors or insulators.

On the other hand, most compounds are insulators. Thus, metal oxides are insulators

(e.g., Al2O3) or semiconductors (such as Cu2O—the reason why it is possible to make

good electrical contacts to partly oxidized copper wires). We will see that this

incredible variation in the electronic properties of materials has its origin in their

quantum mechanical band structure.

Table .1. Resistivities of various materials at 20 C

3.8 Electrons in nanostructures and quantum effects

The electronic properties of bulk materials are dominated by electron

scattering. This acts like a frictional force, so that the electron travels at a “drift

velocity” such that the force owing to an applied field (field = voltage drop per unit

distance, force = charge × field) is just equal to the friction force. Since the current is

proportional to the drift velocity of the electrons, we can see why current is

proportional to voltage in most conductors (i.e., Ohm’s law is obeyed). The scattering

events that contribute to resistance occur with mean free paths that are typically tens

of nm in many metals at reasonable temperatures. Thus, if the size of a structure is of

the same scale as the mean free path of an electron, Ohm’s law may not apply. The

transport can be entirely quantum at the nanoscale. Another nanoscale phenomenon

occurs if the structure is so small that adding an electron to it causes the energy to

shift significantly (compared to kBT)

3.9 Fermi liquids and the free electron model

The free electron model treats conduction electrons as a gas of free, non

interacting particles, introducing interactions only as a means for particles to

exchange energy by scattering. It was introduced by Drude, who justified it solely on

the basis of the results produced by a simple model based on this assumption. It is

remarkable that the Drude model works. To begin with, it ignores the long-range

Coulomb repulsion between electrons. Even more seriously, we now know that the

19

Pauli principle means that most electrons in a material are forbidden from moving

anywhere (Drude’s model predated quantum mechanics). The explanation of why the

free electron model works is subtle. It was first proposed, as a hypothesis, by Landau

who called it the “Fermi liquid” model of metals, a model that has been remarkably

successful in explaining the electrodynamics of metals.1 The Landau hypothesis has

been proved rigorously, but here will only sketch the basic idea.

Figure .10. is a plot of the thermal average occupation number as a function of

temperature for Fermions reproduced from .6. with plots for zero temperature and a

temperature corresponding to 0.05µ (µ is the chemical potential). The chemical

potential at T = 0 is called the Fermi energy, the energy of the highest occupied state

at zero temperature. Mobile particles are produced only because thermal fluctuations

promote electrons from below the Fermi energy to above it. Thus carriers are not

produced alone, but in pairs, corresponding to a net positive charge in a state below

the Fermi level, and a net negative charge in a state above it. This association between

an electron and its “correlation hole” is part of the reason that Coulomb interactions

may be ignored.

Figure .10. Fermi liquid theory of a metal. The carriers are not the electrons

themselves (which are immobile at low temperature) but “quasiparticles” formed

when an electron is excited above the Fermi energy by a thermal fluctuation, leaving

behind a “hole” or antiparticle.

4. ELECTRONS NANOSTRUCTURES APPLICATION

Nanoelectronics refer to the use of nanotechnology in electronic components.

the section covers a diverse set of devices and materials, with the common

characteristic that they are so small that inter-atomic interactions and quantum

mechanical properties need to be used extensively. Some of these include: hybrid

molecular/semiconductor electronics, one-dimensional nanotubes/nanowires, or

advanced molecular electronics. Recent silicon CMOS technology generations, such

as the 22 nanometernode, are already within this regime. Nanoelectronics are

sometimes considered as disruptive technology due to the significantly different from

traditional transistors.

4.1 Nanoelectronic Devices

Nanotechnology Makes many Nanoelectronic digital Devices such as:

• Nano Transistors

20

• Nano Memory

• Nano Circuitry

• Nano Diodes

• OLED (Organic Light Emitting Diode)

• Plasma Displays

• Quantum Computers

• Nano sensors

• Nano rods

• I pods

• Nanogears

Electrodes made from nanowires enable flat panel displays to be flexible as

well as thinner than current flat panel displays. Nanolithography is used for

fabrication of chips. The transistors are made of nanowires, that are assembled on

glass or thin films of flexible plastic. E-paper, displays on sunglasses and map on car

windshields.

4.1.1 Nanoelectronic Transistors

Nanoelectronic Transistors made using Current high-technology production

processes are based on traditional top down strategies, where nanotechnology has

already been introduced silently. The critical length scale of integrated circuits is

already at the nanoscale (50 nm and below) regarding the gate length of transistors

in CPUs or DRAM devices.

Nanoelectronics holds the promise of making computer processors more

powerful than are possible with conventional semiconductor fabrication techniques. A

number of approaches are currently being researched, including new forms

of nanolithography, as well as the use of nanomaterials such as nanowires or small

molecules in place of traditional CMOS components. Field effect transistors have

been made using both semiconducting carbon nanotubes[8]

and with heterostructured

semiconductor nanowires.[9]

In 1999, the CMOS transistor developed at the Laboratory for Electronics and

Information Technology in Grenoble, France, tested the limits of the principles of the

MOSFET transistor with a diameter of 18 nm (approximately 70 atoms placed side by

side). This was almost one tenth the size of the smallest industrial transistor in 2003

(130 nm in 2003, 90 nm in 2004, 65 nm in 2005 and 45 nm in 2007). It enabled the

theoretical integration of seven billion junctions on a €1 coin. However, the CMOS

transistor, which was created in 1999, was not a simple research experiment to study

how CMOS technology functions, but rather a demonstration of how this technology

functions now that we ourselves are getting ever closer to working on a molecular

scale. Today it would be impossible to master the coordinated assembly of a large

number of these transistors on a circuit and it would also be impossible to create this

on an industrial level [23].

21

Transistors Nano Transistor

Figure .11. Simulation result for formation of inversion channel (electron density)

and attainment of threshold voltage (IV) in a nanowire MOSFET. Note that the

threshold voltage for this device lies around 0.45V.

4.1.2 Memory Storage

Electronic memory designs in the past have largely relied on the formation of

transistors. However, research into crossbar switch based electronics have offered an

alternative using reconfigurable interconnections between vertical and horizontal

wiring arrays to create ultra high density memories. Two leaders in this area

are Nantero which has developed a carbon nanotube based crossbar memory

called Nano-RAM and Hewlett-Packard which has proposed the use

of memristor material as a future replacement of Flash memory.

An example of such novel devices is based on spintronics. The dependence of

the resistance of a material (due to the spin of the electrons) on an external field is

called magneto resistance. This effect can be significantly amplified (GMR-Giant

Magneto-Resistance) for nanosized objects, for example when two ferromagnetic

layers are separated by a nonmagnetic layer, which is several nanometers thick (e.g.

Co-Cu-Co). The GMR effect has led to a strong increase in the data storage density of

hard disks and made the gigabyte range possible. The so-called tunneling magneto

resistance (TMR) is very similar to GMR and based on the spin dependent tunneling

of electrons through adjacent ferromagnetic layers. Both GMR and TMR effects can

be used to create a non-volatile main memory for computers, such as the so-called

magnetic random access memory or MRAM

4.2 Novel Optoelectronic Devices Electronic and optoelectronic devices, from computers and smart cell phones to solar

cells, have become a part of our life. Currently, devices with featured circuits of 45 nm in size

can be fabricated for commercial use. However, further development based on traditional semiconductor is hindered by the increasing thermal issues and the manufacturing cost.

During the last decade, nanocrystals have been widely adopted in various electronic

and optoelectronic applications. They provide alternative options in terms of ease of

processing, low cost, better flexibility, and superior electronic/optoelectronic properties. By taking advantage of solution-processing, self-assembly, and surface engineering, nanocrystals

22

could serve as new building blocks for low-cost manufacturing of flexible and large area

devices. Tunable electronic structures combined with small exciton binding energy, high luminescence efficiency, and low thermal conductivity make nanocrystals extremely

attractive for FET, memory device, solar cell, solid-state lighting/display, photodetector, and

lasing applications. Efforts to harness the nanocrystal quantum tunability have led to the

successful demonstration of many prototype devices, raising the public awareness to the wide range of solutions that nanotechnology can provide for an efficient energy economy. This

special issue aims to provide the readers with the latest achievements of nanocrystals in

electronic and optoelectronic applications, including the synthesis and engineering of nanocrystals towards the applications and the corresponding device fabrication,

characterization and computer modeling.

Furthermore, in the modern communication technology traditional analog

electrical devices are increasingly replaced by optical or optoelectronic devices due to

their enormous bandwidth and capacity, respectively. Two promising examples

are photonic crystals and quantum dots . Photonic crystals are materials with a

periodic variation in the refractive index with a lattice constant that is half the

wavelength of the light used. They offer a selectable band gap for the propagation of a

certain wavelength, thus they resemble a semiconductor, but for light

or photons instead of electrons. Quantum dots are nanoscaled objects, which can be

used, among many other things, for the construction of lasers. The advantage of a

quantum dot laser over the traditional semiconductor laser is that their emitted

wavelength depends on the diameter of the dot. Quantum dot lasers are cheaper and

offer a higher beam quality than conventional laser diodes.

4.2.1 Displays

The production of displays with low energy consumption might be

accomplished using carbon nanotubes (CNT). Carbon nanotubes are electrically

conductive and due to their small diameter of several nanometers, they can be used as

field emitters with extremely high efficiency for field emission displays (FED). The

principle of operation resembles that of the cathode ray tube, but on a much smaller

length scale.

Improving display screens on electronics devices. This involves reducing

power consumption while decreasing the weight and thickness of the screens.

Increasing the density of memory chips. Researchers are developing a type of

memory chip with a projected density of one terabyte of memory per square inch or

greater. Reducing the size of transistors used in integrated circuits. One researcher

believes it may be possible to "put the power of all of today's present computers in the

palm of your hand".

4.2.2 Quantum Computers

Entirely new approaches for computing exploit the laws of quantum

mechanics for novel quantum computers, which enable the use of fast quantum

algorithms. The Quantum computer has quantum bit memory space termed "Qubit"

for several computations at the same time. This facility may improve the performance

of the older systems.

4.2.3 Radios

Nanoradios have been developed structured around carbon nanotubes.

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4.2.4 Energy Production

Research is ongoing to use nanowires and other nanostructured materials with

the hope to create cheaper and more efficient solar cells than are possible with

conventional planar silicon solar cells.[12]. It is believed that the invention of more

efficient solar energy would have a great effect on satisfying global energy needs.

There is also research into energy production for devices that would operate in vivo,

called bio-nano generators. A bio-nano generator is

a nanoscale electrochemical device, like a fuel cell or galvanic cell, but drawing

power from blood glucose in a living body, much the same as how the body

generates energy from food. To achieve the effect, an enzymeis used that is capable of

stripping glucose of its electrons, freeing them for use in electrical devices. The

average person's body could, theoretically, generate 100 watts ofelectricity (about

2000 food calories per day) using a bio-nano generator.[13] However, this estimate is

only true if all food was converted to electricity, and the human body needs some

energy consistently, so possible power generated is likely much lower. The electricity

generated by such a device could power devices embedded in the body (such

aspacemakers), or sugar-fed nanorobots. Much of the research done on bio-nano

generators is still experimental, with Panasonic's Nanotechnology Research

Laboratory among those at the forefront.

4.2.5 Medical Diagnostics

There is great interest in constructing nanoelectronic devices[14][15][16] that

could detect the concentrations of biomolecules in real time for use as medical

diagnostics,[17] thus falling into the category of nanomedicine.[18]

A parallel line of

research seeks to create nanoelectronic devices which could interact with

single cells for use in basic biological research.[19]. These devices are

called nanosensors. Such miniaturization on nanoelectronics towards in vivo

proteomic sensing should enable new approaches for health monitoring, surveillance,

and defense technology [21,22,23].

4.2.6 Nano-Robotics

A nanorobot is a tiny machine designed to perform a specific task or tasks

repeatedly and with precision at nanoscale dimensions, that is, dimensions of a few

nanometer s (nm) or less, where 1 nm = 10 -9

meter. They are nanodevices that will be

used for the purpose of maintaining and protecting the human body against pathogens.

The joint use of nanoelectronics, photolithography, and new biomaterials provides a

possible approach to manufacturing nanorobots for common medical applications,

such as for surgical instrumentation, diagnosis and drug delivery. Potential

applications for nanorobotics in medicine include early diagnosis and targeted drug-

delivery for cancer.

4.2.7 Nanotechnology in Circuitry

To see the circuitry, researchers use an electron microscope or an atomic force

microscope.

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4.2.8 Nano-Sensors

Nanotechnology creates many new, interesting fields and applications for

photonic sensors. Existing uses, like digital cameras, can be enhanced because more

‘pixels’ can be placed on a sensor than with existing technology. In addition, sensors

can be fabricated on the nano-scale so that they will be of higher quality, and possibly

defect free. The end result would be that photos would be larger, and more accurate.

As part of a communication network, photonic sensors will be used to convert optical

data (photons) into electricity (electrons). Nanoscale photonic sensors will be more

efficient and basically receive similar advantages to other materials constructed under

the nanoscale.

4.2.9 Multiplexers

A multiplexer is a device for converting many data streams into one single

data stream, which is then divided into the separate data streams on the other side with

a demultiplexer. The main benefit is cost savings, since only one physical link will be

needed, instead of many physical links. In nano-optics, multiplexers will have many

applications. They can be used as part of a communication network, as well as utilized

on a smaller scale for various modern scientific instruments.

5. ELECTRONICS AND COMPUTERS

5.1 Nanotechnology in Computer Processing

The number of transistors on a chip will approximately double every 18 to 24

months (Moore’s Law) as shown in figure .12. This law has given chip designers

greater incentives to incorporate new features on silicon. Problem of Making Moore's

Law works largely through shrinking transistors, the circuits that carry electrical

signals. By shrinking transistors, designers can squeeze more transistors into a chip.

However, more transistors means more electricity and heat compressed into a smaller

space. Furthermore, smaller chips increase performance but also create the problem

of complexity [24].

25

Figure .12. Exponential Moore's Law Curve Credit: Clayton Hallmark

This was expensive. Improving a microprocessor's performance meant scaling

down the elements of its circuit so that more of them could be packed together on the

chip, and electrons could move between them more quickly. Scaling, in turn, required

major refinements in photolithography, the basic technology for etching those

microscopic elements onto a silicon surface. But the boom times were such that this

hardly mattered: a self-reinforcing cycle set in. Chips were so versatile that

manufacturers could make only a few types — processors and memory, mostly — and

sell them in huge quantities. That gave them enough cash to cover the cost of

upgrading their fabrication facilities, or 'fabs', and still drop the prices, thereby

fuelling demand even further improving display screens on electronics devices. This

involves reducing power consumption while decreasing the weight and thickness of

the screens.

6. NANO ELECTRONICS: APPLICATIONS UNDER

DEVELOPMENT Some of the nanoelectronics areas under development such as:

Improving display screens on electronics devices. This involves reducing

power consumption while decreasing the weight and thickness of the screens.

Increasing the density of memory chips. Researchers are developing a type of

memory chip with a projected density of one terabyte of memory per square

inch or greater.

Reducing the size of transistors used in integrated circuits. One researcher

believes it may be possible to "put the power of all of today's present

computers in the palm of your hand".

26

In addition, Researchers are looking into the following nanoelectronics projects:

Cadmium selenide nanocrystals deposited on plastic sheets have been shown

to form flexible electronic circuits. Researchers are aiming for a combination

of flexibility, a simple fabrication process and low power requirements.

Integrating silicon nanophotonics components into CMOS integrated circuits.

This optical technique is intended to provide higher speed data transmission

between integrated circuits than is possible with electrical signals.

Researchers at UC Berkeley have demonstrated a low power method to

use nanomagnets as switches, like transistors, in electrical circuits. Their

method might lead to electrical circuits with much lower power consumption

than transistor based circuits.

Researchers at Georgia Tech, the University of Tokyo and Microsoft Research

have developed a method to print prototype circuit boards using standard

inkjet printers. Silver nanoparticle inkwas used to form the conductive lines

needed in circuit boards.

Researchers at Caltech have demonstrated a laser that uses a nanopatterned

silicon surfacethat helps produce the light with much tighter frequency control

than previously achieved. This may allow much higher data rates for

information transmission over fiber optics.

Building transistors from carbon nanotubes to enable minimum transistor

dimensions of a few nanometers and developing techniques to

manufacture integrated circuits built with nanotube transistors.

Researchers at Stanford University have demonstrated a method to make

functioning integrated circuits using carbon nanotubes. In order to make the

circuit work they developed methods to remove metallic nanotubes, leaving

only semiconducting nanotubes, as well as an algorithm to deal with

misaligned nanotubes. The demonstration circuit they fabricated in the

university labs contains 178 functioning transistors.

Developing a lead free solder reliable enough for space missions and other

high stress environments using copper nanoparticles.

Using electrodes made from nanowires that would enable flat panel displays to

be flexible as well as thinner than current flat panel displays.

Using semiconductor nanowires to build transistors and integrated circuits.

Transistors built in single atom thick graphene film to enable very high speed

transistors.

Researchers have developed an interesting method of forming PN junctions, a

key component of transistors, in graphene. They patterned the p and n regions

in the substrate. When the graphene film was applied to the substrate electrons

were either added or taken from the graphene, depending upon the doping of

the substrate. The researchers believe that this method reduces the disruption

of the graphene lattice that can occur with other methods.

Combining gold nanoparticles with organic molecules to create a transistor

known as a NOMFET (Nanoparticle Organic Memory Field-Effect

Transistor).

Using carbon nanotubes to direct electrons to illuminate pixels, resulting in a

lightweight, millimeter thick "nanoemmissive" display panel.

Using quantum dots to replace the fluorescent dots used in current

displays. Displays using quantum dots should be simpler to make than current

displays as well as use less power.

27

Making integrated circuits with features that can be measured in nanometers

(nm), such as the process that allows the production of integrated circuits

with 22 nm wide transistor gates.

Using nanosized magnetic rings to make Magnetoresistive Random Access

Memory (MRAM)which research has indicated may allow memory density of

400 GB per square inch.

Researchers have developed lower power, higher density method using

nanoscale magnets called magnetoelectric random access memory (MeRAM).

Developing molecular-sized transistors which may allow us to shrink the

width of transistor gates to approximately one nm which will significantly

increase transistor density in integrated circuits.

Using self-aligning nanostructures to manufacture nanoscale integrated

circuits.

Using nanowires to build transistors without p-n junctions.

Using buckyballs to build dense, low power memory devices.

Using magnetic quantum dots in spintronic semiconductor devices. Spintronic

devices are expected to be significantly higher density and lower power

consumption because they measure the spin of electronics to determine a 1 or

0, rather than measuring groups of electronics as done in current

semiconductor devices.

Using nanowires made of an alloy of iron and nickel to create dense memory

devices. By applying a current magnetized sections along the length of the

wire. As the magnetized sections move along the wire, the data is read by a

stationary sensor. This method is calledrace track memory.

Using silver nanowires embedded in a polymer to make conductive layers that

can flex, without damaging the conductor.

IMEC and Nantero are developing a memory chip that uses carbon nanotubes.

This memory is labeled NRAM for Nanotube-Based Nonvolatile Random

Access Memory and is intended to be used in place of high density Flash

memory chips.

Researcher have developed an organic nanoglue that forms a nanometer thick

film between a computer chip and a heat sink. They report that using this

nanoglue significantly increases the thermal conductance between the

computer chip and the heat sink, which could help keep computer chips and

other components cool.

Researchers at Georgia Tech, the University of Tokyo and Microsoft Research

have developed a method to print prototype circuit boards using standard

inkjet printers. Silver nanoparticle inkwas used to form the conductive lines

needed in circuit boards.

7. EMERGING APPLICATIONS OF RADIATION IN

NANOTECHNOLOGY

Radiation is a type of energy emitted by electromagnetic waves or subatomic

particles. Like any other type it can be completely or partially stored in a suitable

medium or environment where it can produce an effect. The effect produced by

radiation is the actual cause, on the basis of which it can be detected, tracked and

identified. This effect is mainly in the form of ionization, which can be direct

or indirect [1]. Incident radiation which ionizes atoms or molecules in a material and

28

thus creates an electrons and holes which are detected is called direct ioniz in

gradiation. Another type of radiation which excites atom or molecule to a higher

energy state which then decay by the emission of excess energy in the form

of photons and is converted into charge carrier is called indirect ionization [2] The

charged radiationwhich produce direct ionization effect are called alpha and beta rays

where as the other which produced indirectionization are neutrons and gamma rays,

which are also known as neutral radiation.

The International Atomic Energy Agency (IAEA) is promoting the new

development in radiation technologies through its technical cooperation programmes,

coordinated research projects, consultants and technical meetings and conferences.

The Consultants Meeting on Emerging Applications of Radiation Nanotechnology

was hosted by the Institute of Organic Synthesis and Photochemistry in Bologna,

Italy, from 22 to 25 March 2004. The meeting reviewed the status of nanotechnology

worldwide. Applications of radiation for nanostructures and nanomachine fabrication,

especially drug delivery systems, polymer based electronic, solar energy photovoltaic

devises, etc., were discussed during the meeting. The opportunities of radiation

technology applications were amply demonstrated.

The Proceeding of a consultants meeting held in Bologna, Italy, 22–25

March 2004 is a report with topic "Emerging Applications of Radiation

Nanotechnology", it provides basic information on the potential of application of

radiation processing technology in nanotechnology. Development of new materials,

especially for health care products and advanced products (electronics, solar energy

systems, biotechnology, etc.) are the main objectives of R&D activities in the near

future. It is envisaged that the outcome of this meeting will lead to new programmes

and international collaboration for research concerning the application of various

radiation techniques in nanotechnology [25].

A nanosensor is not necessarily a device merely reduced in size to a few

nanometers, but a device that makes use of the unique properties of nanomaterials and

nanoparticles to detect and measure new types of events in the nanoscale. For

example, nanosensors can detect chemical compounds in concentrations as low as one

part per billion, or the presence of different infectious agents such as virus or harmful

bacteria. Communication among nanosensors will expand the capabilities and

applications of individual nano-devices both in terms of complexity and range of

operation. The detection range of existing nanosensors requires them to be inside the

phenomenon that is being measured, and the area covered by a single nanosensor is

limited to its close environment.

A network of nanosensors will be able to cover larger areas and perform

additional in-network processing. In addition, several existing nanoscale sensing

technologies require the use of external excitation and measurement equipment to

operate. Wireless communication between nanosensors and micro- and macrodevices

will eliminate this need. For the time being, it is still not clear how these nanosensor

devices will communicate. [26]

29

8. ADVANTAGES AND DISADVANTAGES OF USING

NANOTECHNOLOGY

8.1 Advantages

8.1.1 Energy Advantages

Nanotechnology may transform the ways in which we obtain and use energy.

In particular, it's likely that nanotechnology will make solar power more economical

by reducing the cost of constructing solar panels and related equipment. Energy

storage devices will become more efficient as a result. Nanotechnology will also open

up new methods of generating and storing energy.

8.1.2 Advantages in Electronics and Computing

The field of electronics is set to be revolutionized by nanotechnology.

Quantum dots, for example, are tiny light-producing cells that could be used for

illumination or for purposes such as display screens. Silicon chips can already contain

millions of components, but the technology is reaching its limit; at a certain point,

circuits become so small that if a molecule is out of place the circuit won't work

properly. Nanotechnology will allow circuits to be constructed very accurately on an

atomic level.

8.1.3 Medical Advantages

Nanotechnology has the potential to bring major advances in medicine.

Nanobots could be sent into a patient's arteries to clear away blockages. Surgeries

could become much faster and more accurate. Injuries could be repaired cell-by-cell.

It may even become possible to heal genetic conditions by fixing the damaged genes.

Nanotechnology could also be used to refine drug production, tailoring drugs at a

molecular level to make them more effective and reduce side effects.

8.1.4 Environmental Effects

Some of the more extravagant negative future scenarios have been debunked

by experts in nanotechnology. For example: the so-called "gray goo" scenario, where

self-replicating nanobots consume everything around them to make copies of

themselves, was once widely discussed but is no longer considered to be a credible

threat. It is possible, however, that there will be some negative effects on the

environment as potential new toxins and pollutants may be created by

nanotechnology.

8.1.5 Economic Upheaval

It is likely that nanotechnology, like other technologies before it, will cause

major changes in many economic areas. Although products made possible by

nanotechnology will initially be expensive luxury or specialist items, once availability

increases, more and more markets will feel the impact. Some technologies and

materials may become obsolete, leading to companies specializing in those areas

30

going out of business. Changes in manufacturing processes brought about by

nanotechnology may result in job losses.

8.1.6 Privacy and Security

Nanotechnology raises the possibility of microscopic recording devices, which

would be virtually undetectable. More seriously, it is possible that nanotechnology

could be weaponized. Atomic weapons would be easier to create and novel weapons

might also be developed. One possibility is the so-called "smart bullet," a

computerized bullet that could be controlled and aimed very accurately. These

developments may prove a boon for the military; but if they fell into the wrong hands,

the consequences would be dire.

8.1.7 Material Advantages

It can be created unique materials and products which are: stronger, lighter, durable

and precise.

8.2 Disadvantages Loss of jobs (in manufacturing, farming, etc)

Carbon Nanotubes could cause infection of lungs

Atomic weapons could be more accessible and destructive

9. CONCLUSION

A variety of micromaterials and Nanomaterials have been synthesized that exhibit

unique mechanical, electrical, and photonic properties, and have been used as

functional elements in device applications. For example, self-assembly of silica

microspheres resulted in a photonic crystal with a complete three-dimensional

bandgap [1]. Semiconductor nanowires were used to construct nanoelectronic circuits

[2], solar cells [3], and nanosensors for the detection of biological and chemical

species [4]. Device construction usually requires the positioning of micro and

nanomaterials. Taking one-dimensional nanomaterials as an example,

nanowires/nanotubes need to be positioned between source and drain electrodes for

building nanotransistors and biosensors. To position relatively large amounts of

materials simultaneously, large-scale methods are used, namely, self-assembly [1],

contact printing [5], and dielectrophoresis [6]. However, these methods represent

probabilistic strategies and are not capable of precision control of individual

materials. By contrast, mechanical manipulation, despite being slow in comparison

with the aforementioned large-scale methods, promises specificity, precision, and

programmed motion, and thus, can enable the precise manipulation of individual

materials. For the manipulation of micromaterials, a micromanipulator under an

optical microscope is used. The end-effector can be either a microprobe or a

microgripper. Owing to the strong adhesion forces (capillary forces, electrostatic

forces, and van der Waals forces) at the microscale, manipulation is unreliable and

has low repeatability, motivating the development of suitable manipulation tools and

strategies.

Nanotechnology with all its challenges and opportunities will become a part of

our future. The researchers are optimistic for the products based upon this technology.

Nanotechnology is slowly but steadily ushering in the new industrial revolution.

31

Nanotechnology may offer new ways of working for electronics.

Nanotechnology science is developing new circuit materials, new processors, new

means of storing information and new manners of transferring information.

Nanotechnology can offer greater versatility because of faster data transfer, more “on

the go” processing capabilities and larger data memories. A new field is emerging in electronics that will be a giant leap in computer and

electronics science. It is the field of quantum computing and quantum technology. Quantum

computing is area of scientific knowledge aimed at developing computer technology based on

the principles of quantum theory. In quantum computing the “qbit” instead of the traditional bit of information is used. Traditionally, a bit can assume two values: 1 and 0. All the

computers up-to-date are based on the “bit” principle. However, the new “qbit” is able to

process anything between 0 and 1. This implies that new types of calculations and high processing speeds can be achieved.

Quantum computers have been more of a research area until now. But

recently, the first quantum computer has been built in the United States, according to

a recent paper published on the prestigious scientific journal Nature Physics. This

new computer is said to achieve unseen processing speeds to the tune of a billion

times per second, making this the fastest chip on earth.

We are bound to see many nanotechnological applications within the

electronic industry in the near future. These will undoubtedly increase the quality of

life of our society.

Future of Nanotechnology No one knows for sure. History shows that

science and technology impact society, but there is no way to predict what new

scietific discoveries are next how technology will be used.

Electronic Paper

Nokia Morph

Contact Lens

Nanoelectronics increases the capabilities of electronics devices while

reduces their weight and power consumption. Therefore the Nanoelectronics is used

in wireless radiation sensor since they need small weight and low power consumption

to increase the life time of sensor. previously most of the work has been done in

developing a radiation sensor using nanostructures material i.e. CNTs as well as BN-

based compound. The results for neutron sensing showed that CNTs based sensors

failed due to uncontrolled helicity and small cross-section area for neutron. BN-based

sensor failed due to polarization and non-uniform electric field. So in order to develop

a suitable radiation sensor for neutron, the following challenges need to be addressed:

1) The availability of the suitable material with excellent electrical and mechanical

properties. 2) The size of the sensor which affect the spatial resolution. 3) High bias

voltage. 4) Production of non-uniform electric field. 5) Polarization phenomena in

case the material used are made of a compound of two different elements with

different electro-negativity. There is a possibility that BNNTs array could be used in

the sensor as a sensing element because of the following reasons: 1) It has almost

similar properties to CNTs. 2) BNNTs array consists of large number of vertically

aligned BNNTs. The tip of each BNNT has a large number of electrons that produces

uniform electric field. The uniform electric field thus produced is used to lower the

bias voltage and the smaller size of the BNNTs will result in high spatial resolution.

3) The polarity in the case of BNNTs is piezoelectric with a piezoelectric value of

0.25-0.4 C/cm2 , which is very small compared to Young modulus (1.18 TPa),

therefore the polarization will almost be negligible, resulting in maximum

performance.

32

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