Nanomaterials PDF

CHAPTER- I INTRODUCTION TO NANOMATERIALS Introduction: Nanomaterials: Definition - Classification based on dimensions - Size dependent properties. Types of nanomaterials: Nanoparticles: Synthesis by chemical reduction method. Nanoporous materials: Synthesis by sol-gel meth...

CHAPTER- I INTRODUCTION TO NANOMATERIALS Introduction: Nanomaterials: Definition - Classification based on dimensions - Size dependent properties. Types of nanomaterials: Nanoparticles: Synthesis by chemical reduction method. Nanoporous materials: Synthesis by sol-gel method. Nanowires: Synthesis by VLS mechanism. Carbon Nanotubes (CNTs): Single walled and multi walled nanotubes - Mechanical and electrical properties of CNTs - Applications of CNTs - Synthesis of CNTs by electric arc discharge method and laser ablation method. 1.1 INTRODUCTION Nano science and technology is a broad and interdisciplinary area growing explosively worldwide in the past few years. Nanomaterials are cornerstones of nanoscience and nanotechnology. Now a days in research & development the major sectors are energy, environment, water technology, pharmaceuticals etc. The usage of nanomaterials are enormous as energy storage devices such as fuel cells, detection of threats in defense, navy, drug delivery and water purification. Industrial revolution has made life easy and pleasant. Today’s high speed personal computers and mobile communications would not have certainly been possible without the use of nano science and nano technology. 1.2 MAIN TERMINOLOGY a) Nano science and nanotechnology - The science and technology which deals with the particles in size between 1 to 100nm is known as nano science and nano technology. b) Classification of nanomaterials on the basis of dimensions On the basis of reduction in size of materials in different dimensions, nanomaterials are classified into three groups. Reduction in size in S. No. Size Examples different coordinates 1. 3-dimensions < 100 nm Nanoparticles, quantum dots 2. 2-dimensions < 100 nm Nanotubes, nanowires, nanofibers 3. 1-dimension < 100 nm Thin films, coatings c) Classification based on pore dimensions A useful way to classify nanoporous materials is by the diameter size of their pores, since most of the properties, which are interesting for the applications of adsorption and diffusion are dependent on this parameter. The prefix nano- means a typical dimension between 1 and 100 nm. In this range material properties change drastically, when materials interact with other molecules. In fact, pore diameter establishes the size of molecules that could diffuse inside and comparison between the pore size and the dimension of guest molecule gives an idea about diffusion and interaction properties. If the two dimensions are same, we can expect that the molecule-wall interaction will be prevalent along with the molecule-molecule interaction. By the other way, if guest molecules are smaller than the pore size, there will be less molecule wall interaction than the molecule-molecule interaction during the diffusion process. According to IUPAC definition, nanoporous materials are classified in three main groups depending on their pore dimension: Microporous materials (d99.995% purity) g) Conforms homogeneously to contours of substrate surface h) Controllable thickness and morphology  i) Forms alloys j) Coats internal passages with high length-to-diameter ratios k) Simultaneously coat multiple components l) Coats powders 1.7.3 Applications a) CVD can be used for the synthesis of nanotubes and nanowires. b) CVD can be used for hard coatings and metal films which are used in microelectronics. c) CVD can also be used for preparing semiconducting devices, dielectrics, energy conversion devices etc. d) CVD processes are used on a surprisingly wide range of industrial components from aircraft and land gas turbine blades, timing chain pins for the automotive industry, radiant grills for gas cookers and items of chemical plant to resist various attacks by carbon, oxygen and sulphur. e) Surface modification to prevent or promote adhesion. f) Photoresist adhesion for semiconductor wafers Silane/substrate adhesion for microarrays (DNA, gene, protein, antibody, tissue). g) BioMEMS and biosensor coating to reduce "drift" in device performance. h) Promote biocompatibility between natural and synthetic materials Copper capping Anti- corrosive coating 1.8 PHYSICAL VAPOUR DEPOSITION Nanomaterials in the form of thin films, multilayer films, nanoparticles and nanotubes can be produced by physical vapour deposition methods. Definition Physical vapour deposition (PVD) is a technique by which a metal, ceramic or a compound can be converted into gaseous form and then deposited on the surface of a substrate. In general, PVD methods are subdivided into: 1. Evaporation 2. Sputtering 3. Pulsed Laser Deposition or Laser Ablation EVAPORATION The source materials used in this process are generally refractory metals such as W, Ta, Mo etc. In evaporation technique, both substrate and source materials (to be deposited) are placed inside the vacuum chamber (10-6 to 10-7 torr). The vacuum is required to allow the molecules to evaporate and to move freely in the chamber. An electron gun (e-gun) is used to produce electron beam of 10 keV. This beam is directed at the source material in order to develop sufficient vapour so as to produce deposits on wafer or substrates. Figure.1.7 shows the schematic diagram of evaporation equipment.  Fig. 1.7 Schematic diagram of evaporation equipment SPUTTERING The source materials used in this process are generally an alloy, ceramic or a compound. In sputtering technique, a high energy atom in ionized form usually Ar+ is used to hit the surface atoms of the targeted source material. Then the knocked out atoms in vapour form are deposited on the surface of the substrate to produce a uniform coatings. Fig. 1.8: Schematic diagram of sputtering equipment Pulsed Laser Deposition or Laser Ablation Pulsed Laser Deposition (PLD) is a thin film deposition technique that is used to deposit materials on substrates. A base system consists of a target, substrate carrier which is mounted in a vacuum chamber. An excimer laser is used to energize the surface of a target to produce a deposition plume. The plume is typically directed towards the substrate where a thin-film is deposited. Since each shot of the laser is directly related to the amount of material ablated, the deposition rate can be calibrated and controlled very precisely. Figure.1.9 shows the schematic diagram of pulsed laser deposition.  Fig.1.9: Schematic diagram of Pulsed Laser Deposition Advantages  Ultrapure films or particles can be produced by PVD since it uses a vacuum environment.  PVD can provide good structural control by careful monitoring of the processing conditions.  Materials can be deposited with improved properties compared to the substrate material.  Almost any type of inorganic material can be used as well as some kinds of organic materials.  The process is more environmentally friendly than processes such as electroplating. Disadvantages  Since PVD operates in a low pressure range, it increases the complexity of deposition and cost of production.  It is a line of sight technique meaning that it is extremely difficult to coat undercuts and similar surface features.  High capital cost.  Some processes operate at high vacuums and temperatures requiring skilled operators.  Processes requiring large amounts of heat require appropriate cooling systems.  The rate of coating deposition is usually quite slow. Applications  PVD is used to produce the deposit of various metals, alloys or compounds in the form of coatings or films for: Optics (Ex: Antireflection coatings) Electronics (Ex: Metal contacts) Mechanics (Ex: hard coatings on tools) etc.  PVD coatings are generally used to improve hardness, wear resistance and oxidation resistance.  PVD coatings use in a wide range of applications such as: Aerospace  Automotive Surgical/Medical Dies and moulds for all manner of material processing Cutting tools Fire arms 3030 1.9 APPLICATIONS OF NANOMATERIALS Nowadays in many aspects of our lives more and more materials with new properties are required to ensure further development of mankind. The appearance of nanomaterials has given a great impulse to further discoveries in various fields of science. Nanomaterials with attractive electronic, optical, magnetic, thermal and catalytic properties have attracted great attention due to their widespread applications in physics, chemistry, biology, medicine, material science and interdisciplinary fields. Some basic distinctive properties of nanomaterials are a very small particle size, the large surface area, accelerating the interaction between nanomaterials and the environment in which they are placed as well as the absence of point defects resulting in strength of nanomaterials ten times the strength of steel. These properties explain the fact that even a gram of a nanomaterial may be more effective than a large number of ordinary matters. Today nanomaterials have been used in such areas as:  Production technologies  Military engineering  Nuclear power engineering  Electronic equipment  Protection of materials surface  Medicine and biotechnology Production technologies:  It is important and perspective now to use nanomaterials in composites as components of various functions.  In the production of steels and alloys adding nanopowders helps to reduce porosity and improve the range of mechanical properties.  Manifestation of superplasticity in nanostructured aluminum and titanium alloys makes their use promising in the manufacture of complex shapes details and for using as a connecting layer in welding different solid state materials.  Very large specific surface nanopowders promote their use in a number of chemical processes as catalysts. Military engineering:  Ultra-fine powders are used in a number of radar absorbing coatings for aircraft, created with the use of technology "Stealth", and promising types of explosives and incendiary.  Carbon nanofibers are used in special ammunition intended for the scrapping of the enemy power systems (so-called "graphite bomb"). Nuclear power engineering: The beginning of nuclear power engineering was given by the ultra-fine powders. These powders are commonly used in industrial processes for the separation of uranium isotopes. Prospects for the development of nuclear energy by bringing the particles to the nanostate are mainly associated with a decrease in the average consumption of natural uranium. This happens mostly at the expense of increasing the depth of the nuclear fuel combustion. To do this, scientists are exploring the possibility of the creation of coarse-grained structures of nuclear materials, which can be porous. These nanomaterials will promote a high retention of fission products. Material surface protection: In some cases, for reliable operation, it is necessary to ensure the high water and oil repellency properties of material surface. Some examples of such products may be car windows, glass planes and ships, protective clothing, wall storage tanks for liquids, building construction, etc. At present the titanium oxide nanoparticles coating with sizes of 20-50 nm and a polymer binder have been developed. This coating greatly reduces the wettability of the surface with water, oil and alcohol solutions. Medicine and biotechnology: A number of areas in which nanotechnology is used successfully are as follows: 1. Delivery of drugs (molecules) to the target. Targeted drug delivery in cancer therapy will resolve several issues such as protecting drugs from degradation and adversing interactions with biological molecules. Also increasing the selectivity of drug absorption by tumor cells, controlling of pharmacokinetics, increasing bioavailability of drugs into tumor cells. Apart from the drugs nanoparticles can deliver genes into cells. 2. Treatment and prosthetics using nanomaterials: The unique properties of nanomaterials allow to produce various implants and dentures. With the use of nanotechnology we can get safe, biocompatible and durable implants. 3. Diagnostics: The development of nanotechnology in biomedicine due to improved technology helps to obtain the images, characterization and analysis of biological material, providing a high degree of resolution. Magnetic nanomaterials are an important source for the production of biosensors. The most commonly used nanoparticles are based on the iron oxide coated with various polymers. The surface can be modified by various biospecific ligands as well. Thus the shell protects the iron oxide nanoparticles from chemical interaction with molecules of cells and tissues. Some nanomaterials are also used as electrochemical sensors (nanotubes and nanoparticles) for diagnostics. Electronic equipment: Nanotechnology in Electronics was given a boost by using carbon nanotubes. They are not only able to replace the transistors, but also give the revolutionary electronic circuits their new mechanical and optical properties to create flexible and transparent electronics. The nanotubes are more mobile and do not hold the light in a thin layer, so that the experimental matrix integrated circuit can be bent without loss of the electronic properties. Another application of nanotechnology in electronics is the creation of a new type of hard disks. In 2007, the Nobel Prize in Physics was awarded to Peter Grunberg and Albert Fert for the discovery of the giant magneto resistance effect or, as some authors call it, GMR-effect. On the basis of this effect, it is possible to create magnetic field sensors that can exactly read the information recorded on the hard disk with almost the atomic density. One more prospective application of nanomaterials is producing solar cells. The solar cells that are made on the basis of nanowires instead of the traditional metal wires can increase fifteen times the amount of energy received by a battery. Conductor nanoscale has unique properties of the light absorption. Using nanostructured materials in the manufacturing of the solar cells can improve their efficiency and reduce their cost.  Silver nanoparticles have good antibacterial properties are used in surgical instruments, refrigerators, air-conditioners, water purifiers etc.   Gold nanoparticles are used in catalytic synthesis of silicon nanowires, sensors carrying the drugs and in the detection of tumors.  ZnO nanoparticles are used in electronics, ultraviolet (UV) light emitters, piezoelectric devices and chemical sensors.  TiO2 nanoparticles 2 are used as photocatalyst and sunscreen cosmetics (UV blocking pigment).  Antimony-Tin-Oxide (ATO), Indium-Tin-Oxide (ITO) nanoparticles are used in car windows, liquid crystal displays and in solar cell preparations.  Nanoscale structures and materials such as nanoparticles, nanowires, nanofibers, and nanotubes have been explored in many biological applications e.g., biosensing, biological separation, molecular imaging, and/or anticancer therapy because of their novel properties and functions differ drastically from their bulk counterparts.  Their high volume/surface ratio, surface tailorability, improved solubility, and multifunctionality open many new possibilities for biomedicine.  The intrinsic optical, magnetic and biological properties of nanomaterials offer remarkable opportunities to study and regulate complex biological processes for biomedical applications in an unprecedented manner.  General applications of these materials are found in water purification, wastewater treatment, environmental remediation, food processing and packaging, industrial and household purposes, medicine and in smart sensor development.  The nanomaterials are also used in agriculture production and crop protection.  Nanomaterials prepared from metals, semiconductors, carbon or polymeric species, shaped into nanoparticles and nanotubes have been widely investigated for their ability as electrode modification materials to enhance the efficiencies of electrochemical biosensors. 1.10 CARBON NANOTUBES Carbon is the lightest atom in column IV of the periodic table and is an element with unique and significant properties. It can bind itself or to other light atoms, giving rise to organic chemistry and therefore to biochemistry and the miracle of life on earth. Carbon based materials are unique in several ways. Carbon forms a wide variety of allotropic forms like graphite, diamond, etc. In 1991, Sumio Iijima presented transmission electron microscopy observations of elongated and concentric layered microtubules made of carbon atoms. This propelled the research related to one of the most actively investigated structures of the last century – nowadays called the carbon nanotubes (CNTs). Following Iijima’s ground breaking discovery of multiwall carbon nanotubes (MWCNTs), carbon nanostructures – and in particular carbon nanotubes – have been at the forefront of scientific research in physics, chemistry, materials science, and so on. The discovery of single-wall carbon nanotubes (SWCNTs) in 1993 set yet another milestone in an exponentially growing field. Conceptually, these new nano forms of carbon allotropes with cylindrical geometry belong to the versatile family of fullerenes. Fullerenes were discovered by Harry Kroto, Robert Curl and Richard Smalley in 1985. This nanometer scale structure was named fullerene due to its resemblance to the highly symmetric domes designed by the architect Richard Buckminster Fuller. Buckminster fullerenes or fullerenes are the third allotrope of carbon and consist of a family of spheroidal or cylindrical molecules with all the carbon atoms sp2 hybridized. C60 was the first fullerene to be discovered. Called the bucky ball, it is a soccer ball (icosahedral) shaped molecule with 60 carbon atoms bonded together in pentagons and hexagons. The carbon atoms are sp2 hybridized, but unlike graphite, they are not arranged in a plane and is made up of 12 pentagons and 20 hexagons arranged in a spherical shape. The tubular form of the fullerenes are called carbon nanotubes. Carbon nanotubes have attracted a lot of researchers in a wide range of fields from academia to industry, not only because of their uniqueness when compared with conventional materials, but also because they are very promising materials in nanotechnology. 1.10.1 Types of Carbon Nanotubes A carbon nanotube is a tube-shaped material, made of carbon, having a diameter measuring on the nanometer scale. To understand the structure of a carbon nanotube it can be first imagined as a rolled up sheet of graphene, which is a planar-hexagonal arrangement of carbon atoms distributed in a honeycomb lattice. A single layer of graphite sheet is called graphene. Carbon Nanotubes have many structures, differing in length, thickness, and in the type of helicity and number of layers. As a group, CNTs typically have diameters ranging from