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THE ROLE OF IN ELECTRONIC PROPERTIES OF MATERIALS

Technical Report · June 2016

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Magy M. Kandil Egyptian Nuclear and Radiological Regulatory Authority

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THE ROLE OF NANOTECHNOLOGY IN ELECTRONIC PROPERTIES OF MATERIALS

DR. Magy Mohamed Kandil

CONTENTS

Contents…………..…………………………..…………………………...……………………….....….i Abstract …………..……………………………..………………………...……………………………..1 1.Introduction ……………………………………………………………………..…………………….1 1.1 Nanoscience And ……………………………………………………………….1 1.2 The Scale…………………………….…………………………….……………………1 1.3 Quantum Effects & 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 …………………………………….……………….……….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 …………….…………………………...……………… …………………...... 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- …………….…………………………...………...... ………..…. ….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

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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

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

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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

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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 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 sheets. There are two types of CNT: single- walled (one tube) or multi-walled (several concentric tubes). Both of these are typically a few 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 ), 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

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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

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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 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 , a machine that can produce a desired structure or device atom- by-atom using the principles of [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.

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• 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 (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.

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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

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Feynman's provocative 1959 talk "There's Plenty of Room at the Bottom" while preparing his initial scientific paper on the subject, “: 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 : 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 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].

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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.

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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

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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 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.

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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].

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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.

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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 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

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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 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

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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 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

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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

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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

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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

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• 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. 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].

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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 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

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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 .[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 in medicine include early diagnosis and targeted drug- delivery for .

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].

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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".

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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.

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 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

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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 or harmful . 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]

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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 "" 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

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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.

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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.

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