Nanotechnology Notes by Jaideep Aluru

it is very much useful fir b tech students

1. Done by Aluru Jaideep Reddy Vardhaman college Of engineering

2. Nanomaterials Nanomaterials are defined as those materials which have structured components with size less than 100nm atleast in one dimension. Materials that are nanoscale in one dimension are layers such as thin films or surface coatings. Materials that are nanoscale in two dimensions are nano wires and nano tubes. Materials that are nanoscale in three dimensions are precipitates colloids and quantum dots. The nanostructured materials are materials where the dimensions are in the range of 1 to 100nm (i.e. from the size of the atom to the wavelength of the light.) Nano Science Nanoscience can be defined as the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a large scale. Nanotechnology Nanotechnology can be defined as the design, characterization, production and application of structures, devices and systems by controlling shape and size at the nanometre scale.

3. TYPES OF NANOMATERIALS Most current Nanomaterials could be organized into four types:  1. Carbon Based Materials          2. Metal Based Materials          3. Dendrimers          4. Composites CARBON BASED NANOMATERIALS These nanomaterials are composed mostly of carbon, most commonly taking in the form of hollow spheres, ellipsoids, or tubes. Spherical and ellipsoidal carbon nanomaterials are referred to as fullerenes, while cylindrical ones are called nanotubes . These particles have many potential applications, including improved films and coatings, stronger and lighter materials, and applications in electronics.

4. METAL BASED NANOMATERIALS These nanomaterials include quantum dots, nanogold , nanosilver and metal oxides, such as titanium dioxide. A quantum dot is a closely packed semiconductor crystal comprised of hundreds or thousands of atoms, and whose size is on the order of a few nanometers to a few hundred nanometers. Changing the size of quantum dots changes their optical properties. DENDRIMERS These nanomaterials are nanosized polymers built from branched units. The surface of a dendrimer has numerous chain ends, which can be tailored to perform specific chemical functions. This property could also be useful for catalysis. Three-dimensional dendrimers contain interior cavities into which other molecules could be placed, they may be useful for drug delivery. COMPOSITES Composites combine nanoparticles with other nanoparticles or with larger, bulk-type materials. Nanoparticles , such as nanosized clays, are already being added to products ranging from auto parts to packaging materials, to enhance mechanical, thermal, barrier, and flame-retardant properties.

5. Why the properties of nanoparticles are different? Two principal factors cause the properties of nanomaterials to differ significantly from other materials. 1. Increase in surface area to volume ratio 2. Quantum confinement effects These factors can change the properties such as reactivity, strength and electrical characteristics. 1. Increase in surface area to volume ratio Nanomaterials have a relatively larger surface area when compared to the same volume of the material produced in a larger form. Let us consider a sphere of radius r, Its surface area = 4 π r 2 Its volume = (4/3) π r 3 Surface area to its volume ratio = 3/r. Thus when the radius of the sphere decreases, its surface area to volume ratio increases.

6. Let us consider another example. For one cubic volume, surface area is 6 m 2 . When it is divided into 8 pieces its surface area becomes 12 m 2 . when the same volume is divided into 27 pieces its surface area becomes 18 m 2 . Thus we find that when the given volume is divided into smaller pieces its surface area increases. Hence as particle size decreases its surface area increases. (Surface area of cube = 6a 2 ) Thus nanoparticles have a greater surface area per given volume compared with large particles. It makes materials more reactive. As growth and catalytic chemical reactions occur at surfaces, this means that a given mass of material in nanostructure form will be much more reactive than the same mass of material made up of larger particles. This affects their strength or electrical properties.

7. 2. Quantum confinement effects When atoms are isolated, the energy levels are discrete. When very large number of atoms are closely packed to form a solid, the energy levels split and form bands. Nanomaterials represent intermediate stage. We have studied the problems of particles in a potential well as well as in a potential box. When dimensions of such potential boxes or wells are of the order of deBroglie wavelength of electrons, energy levels of electrons change. This effect is called Quantum confinement . When the material is in sufficiently small size typically 10 nm or less, organization of energy levels into which electrons can climb or fall change. Specifically, the phenomenon results from electrons and holes being squeezed into a dimension that approaches a critical quantum measurement, called the “ exciton Bohr radius”. These can affect the optical, electrical and magnetic behaviour of materials, particularly as the structure or particle size approaches the smaller end of the nanoscale .

8. (Properties of Nanomaterials ) Nanoscale Size Effect Manifestation of novel phenomena and properties, including changes in: - Physical Properties (e.g. melting point) - Chemical Properties (e.g. reactivity) - Electrical Properties (e.g. conductivity) - Mechanical Properties (e.g. strength) Optical Properties (e.g. light emission) Magnetic Properties (e.g. Coercivity )

9. Various Properties of Nanomaterials

10. Chemical Properties Mechanical Properties

11. HOW TO SYNTHESIZE? TOP DOWN APPROACH SOL-GEL METHOD BOTTOM UP APPROACH CVD PVD PLVD Approaches Top-down – Breaking down matter into more basic building blocks. Frequently uses chemical or thermal methods. Bottoms-up – Building complex systems by combining simple atomic-level components.

12. Advantages high growth rates possible can deposit materials which are hard to evaporate good reproducibility can grow epitaxial films Disadvantages high temperatures complex processes toxic and corrosive gasses

13. Sol-Gel technique The sol gel process is a wet chemical technique i.e., chemical solution deposition technique used for the production of high purity and homogeneous nanomaterials , particularly metal oxide nano particles. The idea behind sol-gel synthesis is to “dissolve” the compound in a liquid in order to bring it back as a solid in a controlled manner. The starting material from a chemical solution leads to the formation of colloidal suspensions known as ‘sol’. Then the sol evolves towards the formation of an inorganic network containing a liquid phase called the ‘gel’. The removal of the liquid phase from the sol yields the gel. The particle size and shape are controlled by the sol/gel transitions. The thermal treatment (firing/calcinations) of the gel leads to further poly condensation and enhances the mechanical properties of the products, i.e., oxide nanoparticles .

14. The precursors for synthesizing the colloids are metal alkoxides and metal chlorides. The starting material is processed with water or dilute acid in an alkaline solvent. The material undergoes a hydrolysis and poly condensation reaction which leads to the formation of colloids. The colloid system composed of solid particles dispersed in a solvent contains particles of size from 1nm to 1mm. The sol is then evolved to form an inorganic network containing liquid phase (gel). The schematic representation of the synthesis of nanoparticles using the sol gel method is shown in Fig. The sol can be further processed to obtain the substrate in a film, either by dip coating or spin coating, or cast into a container with desired shape or powders by calcinations. The chemical reaction which takes place in the sol gel metal alkoxides M (OR) 2 during the hydrolysis process and condensation is given below: M-O-R +H 2 O M-OH + R-OH (Hydrolysis) M-O-H + R-O-M M-O-M + R-OH (Condensation)

15. The sol-gel method is an interesting, cheap and low temperature technique which is used to produce a range of nanoparticles with controlled chemical compositions. One can produce the aero gel, a highly porous material like glass and glass ceramics, at a very low temperature by controlling the process parameters. The sol gel derived nanoparticles finds wide spread applications in various fields like optics, electronics, energy, space, bio sensors and drug delivery. Advantages Disa dvantages Controlling the growth of the particles is difficult. Stopping the newly formed particles from agglomeration is also difficult

16. Physical vapour deposition ( pvd ) The materials of interest are evaporated and hence, the atoms or molecules are in gas phase. The gas phase atoms or molecules are used to obtain the nanostructured materials in any one of the methods, namely, 1. Evaporation 2. Sputtering 3. Ion plating 4. Laser ablation Let us discuss the experimental set-up used for the synthesis of nanostructured materials in the evaporation method.

17. The schematic representation of the experimental set-up used for the synthesis of nanomaterials by evaporation is shown in figure. It consists of a bell jar, in which an inert gas or reactive gas is filled after vacuum. The materials to be evaporated are placed in the crucibles and are heated either by resistance or an electron gun until sufficient vapour develops. The evaporated atoms or molecules are allowed to condense on a cold finger which is cooled externally by liquid N 2 . The nanoparticles on the cold finger is scraped by the scraper and then collected to the piston anvil through a funnel. The piston anvil is used to obtain the compacted nano powders. The desired purity of the nano powder is obtained since the evaporation is done at the vacuum chamber with the pressure of an inert or reactive gas. This method is more suitable for non-conductive materials or high melting materials. Evaporation

18. Pulsed laser vapour deposition ( plvd ) Introduction Pulsed-laser vapour deposition (PLVD) has gained a great deal of attention in the past few years for its ease of use and success in depositing materials of complex stoichiometry . PLVD was the first technique used to successfully deposit a superconducting YBa 2 Cu 3 O 7-d thin film. Since that time, many materials that are normally difficult to deposit by other methods, especially multi-element oxides, have been successfully deposited by PLVD. Synthesis of Buckminster fullerenes and nanopowders have also been reported by using PLVD. 

19. THE MECHANISM OF PLD The principle of pulsed laser deposition, in contrast to the simplicity of the system set-up, is a very complex physical phenomenon. It does not only involve the physical process of the laser-material interaction of the impact of high-power pulsed radiation on solid target, but also the formation plasma plume with high energetic species and even the transfer of the ablated material through the plasma plume onto the heated substrate surface. Thus the thin film formation process in PLVD generally can be divided into the following four stages. 1. Laser radiation interaction with the target  2. Dynamic of the ablation materials  3. Deposition of the ablation materials with the substrate  4. Nucleation and growth of a thin film on the substrate surface Each stage in PLVD is critical to the formation of quality epitaxial crystalline, stoichiometric , uniform and small surface roughness thin film.

20. THE ADVANTAGES OF PLD The main advantages of Pulsed Laser Deposition are: conceptually simple : a laser beam vaporizes a target surface, producing a film with the same composition as the target. versatile : many materials can be deposited in a wide variety of gases over a broad range of gas pressures. cost-effective : one laser can serve many vacuum systems. fast : high quality samples can be grown reliably in 10 or 15 minutes. scalable : as complex oxides move toward volume production.

21. Nanotechnology Applications Information Technology Energy Medicine Consumer Goods Smaller, faster, more energy efficient and powerful computing and other IT-based systems More efficient and cost effective technologies for energy production Solar cells Fuel cells Batteries Bio fuels Foods and beverages Advanced packaging materials, sensors, and lab-on-chips for food quality testing Appliances and textiles Stain proof, water proof and wrinkle free textiles Household and cosmetics Self-cleaning and scratch free products, paints, and better cosmetics Cancer treatment Bone treatment Drug delivery Appetite control Drug development Medical tools Diagnostic tests Imaging

22. Endless applications of nanotechnology nanomedicines to fight diseases. Nanorobots . Less pollution and automatic clean up. More efficient solar cells. Carbon nanotubes . Ultra light materials for construction. Nanorobots in military applications. Self replicating and self repairing machinery . A supercomputer no bigger than a human cell. High density data storage. And the list goes on………