![Introduction Classification Synthesis
Gas Condensation: 3. Pulsed-laser-ablation
Laser parameters: Laser energy/fluence [Joule/cm2] and
ionization degree.
Surface temperature: Has a large effect on the nucleation
density. Nucleation density decreases as the temperature is
increased. Heating of the surface can involve a heating
plate or the use of a CO2 laser.
Substrate surface: Surface preparation, the miscut of the
substrate, and roughness of the substrate.
Background pressure: Common in oxide deposition, an
oxygen background is needed to ensure stoichiometric
transfer from the target to the film. This will affect the
nucleation density and film quality.
Three growth modes are possible:
1. Step-flow growth 2. Layer-by-layer growth, 3. 3D growth.
K. Sakkaravarthi Lectures in Nanoscience & Technology 32/50](https://image.slidesharecdn.com/nano-introduction-240310180251-52d5f8be/85/nano-introduction-nano-materials-nano-engineering-32-320.jpg)
nano-introduction nano materials nano engineering
- 1. Lectures in Nanoscience & Technology 1. Nanomaterials & Structures K. Sakkaravarthi Department of Physics National Institute of Technology Tiruchirappalli – 620 015 Tamil Nadu India sakkaravarthi@nitt.edu ksakkaravarthi.weebly.com
- 2. Introduction Classification Synthesis Objectives Education and Research for a better scientific understanding on the Preparation & Characterization of Materials in Nanoscales towards enhanced Utilization & Applications. Normal/Bulk materials Nanomaterials K. Sakkaravarthi Lectures in Nanoscience & Technology 2/50
- 3. Introduction Classification Synthesis My sincere acknowledgments to Introduction to Nanoscience and Nanotechnology, Chris Binns, Wiley Publications, New Jersey (2009). Nanotechnology: Basic Sciences and Energy Technologies, M. Wilson, K. Kannangara, G. Smith, M. Simmons and B. Raguse, CRC Press, New York (2005). Introduction to Nanotechnology, C.P. Poole and F.J. Ownes, Wiley India, New Delhi (2007). Introduction to Nanomaterials and Nanotechnology (Lecture Notes: University of Tartu), Vladimir Pokropivny, Rynno Lohmus, Irina Hussainova, Alex Pokropivny, Sergey Vlassov (2007). Many other free & copyright internet resources. K. Sakkaravarthi Lectures in Nanoscience & Technology 3/50
- 4. Introduction Classification Synthesis Nanoscience & Technology Discussion? NANO: Definition for nano? Nanoscience Technology in Nanoscience Need for NANO Utilize the possibility to vary fundamental properties of materials without changing their chemical compositions. The size can change the behavior of the material! K. Sakkaravarthi Lectures in Nanoscience & Technology 4/50
- 5. Introduction Classification Synthesis Nanomaterials Peculiar Reasons? Nanomaterials have a relatively larger surface area compared to the same mass of material produced in a larger/bulk form. This makes materials more chemically reactive (sometimes inert materials in larger bulk form can become reactive when produced in their tiny nanoscale), and affect their (mechanical/electrical/optical/magnetic) properties. Quantum effects begin to dominate the behavior. The mechanical, thermal, optical, electrical and magnetic behaviour of materials exhibit huge difference in the nanoscale size. K. Sakkaravarthi Lectures in Nanoscience & Technology 5/50
- 6. Introduction Classification Synthesis Nanomaterials: Properties Mechanical properties: Surface to volume ratio increases with decreasing size. Grain size, Cavities, dislocation, Strength of materials... Thermal properties: Surface atoms are less constrained than interior atoms and thus can vibrate more freely about their equilibrium. Better specific heat and thermal conductivity in nanomaterials. Also, have lower melting temperature/point. Electrical conductivity: Free electrons yield an energy continuum with no forbidden energy levels. The energy levels become discrete/quantized and then form bands with forbidden zones when move from bulk to nano scale. Hence, bulk metals are good electrical conductors. In the reverse, in nanoscale materials the energy levels will have more forbidden zones & reduces the electrical conductivity of nanomaterials. K. Sakkaravarthi Lectures in Nanoscience & Technology 6/50
- 7. Introduction Classification Synthesis Nanomaterials: Properties... Electrical conductivity: If size decreases bandgap increases! K. Sakkaravarthi Lectures in Nanoscience & Technology 7/50
- 8. Introduction Classification Synthesis Types of Nanomaterials Classification Based on Confined dimensions? 1D nanomaterial: One-dimension in nanoscale range & two other dimensions free (any scale). Ex.: Surface coatings and thin films. 2D nanomaterial: Any two dimensions in nanoscale range & one dimension free. Ex.: Biopolymers, nanotubes, and nanowires. 3D nanomaterial: All three dimensions in nanoscale. Ex. Nanoparticles, Colloids, Quantum dots, fullerenes, etc. 0D nanomaterial: Zero dimensions in nanoscale :-( i.e. Bulk materials in macroscale ) NOT NANO. Violates basic definition ) NOT acceptable But, actual/acceptable classification?? Should be based on the “Number of Free Dimensions!" K. Sakkaravarthi Lectures in Nanoscience & Technology 8/50
- 9. Introduction Classification Synthesis Types of Nanomaterials Classification: Based on the Number of free dimensions! 0D nanomaterial: None can be outside nanoscale. All the three dimensions are in nanoscale range. Ex. Nanoparticles, Colloids, Quantum dots, fullerenes, etc. K. Sakkaravarthi Lectures in Nanoscience & Technology 9/50
- 10. Introduction Classification Synthesis Types of Nanomaterials... Classification: Based on the Number of free dimensions! 1D nanomaterial: One dimension outside the nanoscale & two other dimensions in the nanoscale range. Ex.: Nanowires, Nanorods, Nanotubes & Biopolymers. 2D nanomaterial: Any two dimensions can be outside the nanoscale & one dimension in nanoscale range. Exhibit plate-like shapes! Ex.: Nanolayers, Surface coatings and thin films. 3D nanomaterial: Bulk nanomaterials & all three dimensions can be outside nanoscale. But, made up of a collection of nano-particles/materials. Ex.: Dispersions of nanoparticles, bundles of nanowires/ nanotubes & multiple nanolayers. K. Sakkaravarthi Lectures in Nanoscience & Technology 10/50
- 11. Introduction Classification Synthesis Types of Nanomaterials... Classification: Based on the Number of free dimensions! K. Sakkaravarthi Lectures in Nanoscience & Technology 11/50
- 12. Introduction Classification Synthesis 0D: Nanoparticles (single/composite/coated) K. Sakkaravarthi Lectures in Nanoscience & Technology 12/50
- 13. Introduction Classification Synthesis 1D: Nanowires/Nanorods/Nanotubes K. Sakkaravarthi Lectures in Nanoscience & Technology 13/50
- 14. Introduction Classification Synthesis All-in-One Example Carbon: Basic element of life & its special ability to bond with many elements in different ways. K. Sakkaravarthi Lectures in Nanoscience & Technology 14/50
- 15. Introduction Classification Synthesis Allotropes of carbon: 0D to 3D Eight allotropes of carbon: a) diamond, b) graphite, c) lonsdaleite, d) C60 buckminster fullerene, e) C540, Fullerite f) C70, g) amorphous carbon, and h) single-walled carbon nanotube. K. Sakkaravarthi Lectures in Nanoscience & Technology 15/50
- 16. Introduction Classification Synthesis 1. Nanowires One to few-tens of nanometer (109 m). The ratio of the length-to-width greater than 1000 (aspect ratio: Length Thickness ' 1000). Structures with a thickness/diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important ) “quantum wires". Many different types of nanowires exist. Superconducting, metallic, Semiconducting, & insulating. Ex. Semiconducting nanowires: Silicon, Gallium Nitride and Indium Phosphide. Remarkable optical, electronic and magnetic characteristics! (Silica nanowires can bend light around very tight corners). K. Sakkaravarthi Lectures in Nanoscience & Technology 16/50
- 17. Introduction Classification Synthesis 1. Nanowires: Applications High-density data storage, either as magnetic read heads or as patterned storage media. Electronic and opto-electronic nanodevices. Metallic interconnects of quantum devices and nanodevices. 1. Nanowires: Synthesis Self-assembly processes, where atoms arrange themselves naturally on stepped surfaces. Chemical vapor deposition (CVD) onto patterned substrates Electroplating or molecular beam epitaxy (MBE) K. Sakkaravarthi Lectures in Nanoscience & Technology 17/50
- 18. Introduction Classification Synthesis 2. Nanorods A solid wire-like structure in nanometer-scale. Diameter: One to 100 nanometer (1 100 nm). The ratio of the length-to-width is very small. (aspect ratio: Length Thickness ' 2 20). Structures with a thickness/diameter constrained to tens of nanometers or less and an unconstrained length. 2D view 3D view K. Sakkaravarthi Lectures in Nanoscience & Technology 18/50
- 19. Introduction Classification Synthesis 3. Nanotubes A tube-like (hollow) structure in nanometer-scale. Diameter in the order of nanometer (109 m). The ratio of the length-to-width huge. Aspect ratio: Length Thickness up to 132,000,000 (significantly larger than for any other material). Exceptional strength and stiffness. Nanotubes maybe single-walled or multi-walled! Mainly made of carbon!! K. Sakkaravarthi Lectures in Nanoscience & Technology 19/50
- 20. Introduction Classification Synthesis Synthesis Approaches 1 Top-down: * Breaking down bulk matter into basic building blocks. * Slicing or successive-cutting (crushing, milling or grinding) of a bulk material to get nano sized particles. * Not suitable for preparing uniformly shaped materials. Mainly, chemical or thermal or mechanical methods. 1. Ball milling 2. Plasma arching 3. Laser sputtering 4. Vapour deposition 2 Bottoms-up: * Building complex systems by combining simple atomic-level components. * Devices ‘create themselves’ by self-assembly. * Much cheaper than top-down methods. * Able to generate a uniform size, shape and distribution. * Normally made by chemical synthesis. 1. Sol-gel 2. Colloidal 3. Electrodeposition 4. Solution phase reductions K. Sakkaravarthi Lectures in Nanoscience & Technology 20/50
- 21. Introduction Classification Synthesis Synthesis Approaches... K. Sakkaravarthi Lectures in Nanoscience & Technology 21/50
- 22. Introduction Classification Synthesis Synthesis Approaches... K. Sakkaravarthi Lectures in Nanoscience & Technology 22/50
- 23. Introduction Classification Synthesis Synthesis Approaches... K. Sakkaravarthi Lectures in Nanoscience & Technology 23/50
- 24. Introduction Classification Synthesis 0D Nanoparticles: Ball Milling 1 Grinder used to grind & blend materials. 2 Principle of impact and attrition: Size reduction by impact (balls drop from near the top of the shell). 3 A hollow cylindrical shell rotating about its axis. It is partially filled with balls (made of steel, stainless steel, ceramic, or rubber). 4 The length of the cylindrical mill ⇡ its diameter. 5 Grinding can be carried out either wet or dry (speed). 6 Effective for production of amorphous materials. 7 Properties of balls: size, density, hardness, & composition. 8 Advantages: Cost effective; Suitable for both open & closed grinding and batch & continuous operation; Materials of all degrees of hardness K. Sakkaravarthi Lectures in Nanoscience & Technology 24/50
- 25. Introduction Classification Synthesis 0D Nanoparticles: Ball Milling - Schematic K. Sakkaravarthi Lectures in Nanoscience & Technology 25/50
- 26. Introduction Classification Synthesis 0D Nanoparticles: Ball Milling - Factors to consider K. Sakkaravarthi Lectures in Nanoscience & Technology 26/50
- 27. Introduction Classification Synthesis 0D Nanoparticles: Gas Condensation Inert Gas evaporation-Condensation (IGC) technique: Formation of nano-powders/particles on a metallic source/ substrate without chemical reactivity (inert gas environment). 1 Evaporating a metallic source using resistive heating (radio frequency heating or electron gun or laser beam) inside an evacuated chamber (to about 10 7 torr) filled with inert gas at a low pressure. 2 The metal vapour migrates from the hot source into the cooler inert gas by a combination of convective flow and diffusion. Here the evaporated atoms collide with the gas atoms within the chamber, thus losing kinetic energy. 3 The particles are collected usually by deposition on a cold surface (cooling the substrate with liquid nitrogen to enhance the deposition efficiency). 4 Highly concentrated deposition on the substrate. Have complex aggregate morphology: need to be classified based on the size (smaller or larger structures). K. Sakkaravarthi Lectures in Nanoscience & Technology 27/50
- 28. Introduction Classification Synthesis 0D Nanoparticles: Gas Condensation K. Sakkaravarthi Lectures in Nanoscience & Technology 28/50
- 29. Introduction Classification Synthesis Gas Condensation: 1. Thermal evaporation Most popular technique: easy handling & good yield. Suitable to synthesis several pure nanocrystalline metals (Cu, Au, Pd, Ni, Fe,) with a narrow particle size 5-20 nm. Able to change particle size by varying gas pressure & temp. Cons.: Alloys with different vapor pressures of constituent elements are difficult to make :-( K. Sakkaravarthi Lectures in Nanoscience & Technology 29/50
- 30. Introduction Classification Synthesis Gas Condensation: 2. Magnetron-sputtering Suitable for elements with different vapour pressures. Good for metals with very high melting point (Mo and oxides like ZrO2) - very difficult in thermal evaporation. For thin films: at very low pressures (around 10 3 mbar). For powders/particles: Pressure around 10 1 mbar in IGC. Cannot change the particle size by changing gas pressure :-( K. Sakkaravarthi Lectures in Nanoscience & Technology 30/50
- 31. Introduction Classification Synthesis Gas Condensation: 3. Pulsed-laser-ablation High power laser pulses to melt, evaporate and ionize material from the surface of a target. Pico-second pulsed laser irradiation in a vacuum chamber (base pressure 10 7 mbar) with helium or argon. Ablated atoms condense into clusters/nanoparticles & collected on a liquid nitrogen cooled collection device. Production of superconducting & insulating circuit components to improved wear and biocompatibility. Wider range of nanopowders of metals, metallic alloys, semiconductors, and metal oxides can be synthesized :-) K. Sakkaravarthi Lectures in Nanoscience & Technology 31/50
- 32. Introduction Classification Synthesis Gas Condensation: 3. Pulsed-laser-ablation Laser parameters: Laser energy/fluence [Joule/cm2] and ionization degree. Surface temperature: Has a large effect on the nucleation density. Nucleation density decreases as the temperature is increased. Heating of the surface can involve a heating plate or the use of a CO2 laser. Substrate surface: Surface preparation, the miscut of the substrate, and roughness of the substrate. Background pressure: Common in oxide deposition, an oxygen background is needed to ensure stoichiometric transfer from the target to the film. This will affect the nucleation density and film quality. Three growth modes are possible: 1. Step-flow growth 2. Layer-by-layer growth, 3. 3D growth. K. Sakkaravarthi Lectures in Nanoscience & Technology 32/50
- 33. Introduction Classification Synthesis Electron beam (physical vapor) deposition K. Sakkaravarthi Lectures in Nanoscience & Technology 33/50
- 34. Introduction Classification Synthesis Synthesis: 2D films/layers K. Sakkaravarthi Lectures in Nanoscience & Technology 34/50
- 35. Introduction Classification Synthesis Synthesis: Sol-Gel Wet-chemical process: Formation of an inorganic colloidal suspension (sol) and gelation of the sol in a continuous liquid phase (gel)! K. Sakkaravarthi Lectures in Nanoscience & Technology 35/50
- 36. Introduction Classification Synthesis Synthesis: Sol-Gel K. Sakkaravarthi Lectures in Nanoscience & Technology 36/50
- 37. Introduction Classification Synthesis Synthesis: Sol-Gel K. Sakkaravarthi Lectures in Nanoscience & Technology 37/50
- 38. Introduction Classification Synthesis Spray Pyrolysis Vertical spray set-up K. Sakkaravarthi Lectures in Nanoscience & Technology 38/50
- 39. Introduction Classification Synthesis Spray Pyrolysis 45o spray set-up K. Sakkaravarthi Lectures in Nanoscience & Technology 39/50
- 40. Introduction Classification Synthesis Dip Coating 1 Coating process to manufacture bulk products. 2 Thin-film coatings: Single layer or Multilayer. 3 Suitable for 4 Mainly involves five stages: 1. Immersion: The substrate is immersed in the solution at a constant speed. 2. Start-up: Pulled up back (constant speed) after a while. The speed determines the thickness of the coating. (faster withdrawal gives thicker coating material) 3. Deposition: Thin layer deposits on the substrate. 4. Drainage: Excess liquid is drained from the surface. 5. Evaporation: The solvent evaporates from the liquid. For volatile solvents, such as alcohols, evaporation starts already during the deposition and drainage steps. K. Sakkaravarthi Lectures in Nanoscience & Technology 40/50
- 41. Introduction Classification Synthesis Dip Coating: Schematic 1 K. Sakkaravarthi Lectures in Nanoscience & Technology 41/50
- 42. Introduction Classification Synthesis Dip Coating: Schematic 2 K. Sakkaravarthi Lectures in Nanoscience & Technology 42/50
- 43. Introduction Classification Synthesis Dip Coating: Factors to consider The dip coating technique can give uniform, high quality films even on bulky, complex shapes. 1 Initial substrate surface 2 Submersion time 3 Withdrawal speed 4 Number of dipping cycles 5 Solution composition 6 Concentration and temperature 7 Environmental factors Dip Coating: Few Advantages Single/Multilayer coatings for sensor applications Hydrogels/ Sol-Gel nanoparticle coatings Layer-by-layer nanoparticle assemblies K. Sakkaravarthi Lectures in Nanoscience & Technology 43/50
- 44. Introduction Classification Synthesis Multilayer Materials K. Sakkaravarthi Lectures in Nanoscience & Technology 44/50
- 45. Introduction Classification Synthesis Multilayer Coating: Semiconductor Applications K. Sakkaravarthi Lectures in Nanoscience & Technology 45/50
- 46. Introduction Classification Synthesis Molecular-beam epitaxy Thin-film deposition of single crystals! 1 Epitaxy: Method of depositing a mono crystalline film or deposition and growth of mono crystalline layers. 2 Growing crystalline layers on a crystalline substrate. Similar to Ink-Jet-Color printing!! 3 Widely used in the manufacture of semiconductor devices. 4 1. Homoepitaxy: Same type substrate & material (Si-Si). 2. Heteroepitaxy: Different substrate & material (Ga-As). 3. Pseudo-homoepitaxy: Same material with a doping layer. K. Sakkaravarthi Lectures in Nanoscience & Technology 46/50
- 47. Introduction Classification Synthesis Molecular-beam epitaxy... 1 MBE is an ultra high vacuum (UHV) based based production of high quality epitaxial structures with mono layer (ML) control. 2 “Beam” molecules do not collide to either walls of the vacuum chamber (pressure: 10-11 Torr) or existing gas atoms. 3 Very slow process: Growth rate: 1 m/hr. 4 To produce layers of metals, insulators & superconductors. 5 1. Ultra pure elements are heated in separate quai-effusion cells until they begin to sublimate slowly. 6 2. Epitaxial growth takes place due to the interaction of molecular or atomic beams on the surface of heated crystalline substrate. 7 3. Atoms on a clean surface are free to move until finding correct position in the crystal lattice to bond. K. Sakkaravarthi Lectures in Nanoscience & Technology 47/50
- 48. Introduction Classification Synthesis Molecular-beam epitaxy... K. Sakkaravarthi Lectures in Nanoscience & Technology 48/50
- 49. Introduction Classification Synthesis Molecular-beam epitaxy... 1 Basic elements of MBE system: * Heated substrate. * Effusion cells and shutter. * Reflection High Energy Electron Diffraction (RHEED) system: RHEED gun & screen. * Ultra High Vacuum * Liquid Nitrogen cryopanelling. 2 MBE Working Conditions: * Mean free path of the particles > size of the chamber. * Ultra-high vacuum (UHV= 10-11 Torr) for clear epilayer. * Chemically stable as crucibles even at high temperature. * Molybdenum and tantalum are widely used for shutters. * Ultrapure materials are used as source. 3 Pros: Clean surfaces & free from oxide layer. Good control of layer thickness & composition. Low growth rate (1µm/h) gives high purity. Precisely controllable thermal evaporation of each component. 4 Cons: Expensive (106 $ per MBE chamber). Very complex system. Ultra-high vacuum conditions. K. Sakkaravarthi Lectures in Nanoscience & Technology 49/50
- 50. Introduction Classification Synthesis Molecular-beam epitaxy... Molecular-beam epitaxy: Applications * Heterojunction bipolar transistors (HBT’s) used in satellite communications. * Electronic and optoelectronic devices (LED’s for laser printers, CD/DVD players). * Construction of quantum wells, dots and wires. * To build a thin film of a photo voltaic solar cells. * Low temperature Superconductor. K. Sakkaravarthi Lectures in Nanoscience & Technology 50/50