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Nanoscience and nanotechnology

Nanoscience and nanotechnology 17
Nanochemistry Lecture 1 Dr Charu Arora, Associate Professor, Department of ChemistryNanostructuresNanoscience and nanotechnology • Nanoscience deals with the scientific study of objects with sizes in the 1 – 100 nm range in at least one dimension. • Nanotechnology deals with using objects in the same size range to develop products with possible practical application. It is usually based on nanoscience insights.Nanoscience and Nanochemistry • Nanoscience is interesting in part of course because it by definition is new. But a more profound and important reason is that it deals with objects which are only slightly larger than an atom. This means that the properties of the objects can be influenced by direct manifestations of quantum mechanics. • It is also possible that nanoscale objects do behave just like as expected from (semi)classical physics, but the downgrading in size opens up possible new applications.Research on nano• Nanotechnology is the creation of functional materials, devices, and systems through control of matter on the nanometer (1 to 100 nm) 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.Ancient nanotech. • It is interesting to note that there has been use of what now would definitely be called nanoscience much before the advent of the word. • Vases used by old Greeks and RomansNanotechnology marketNanoscaleDefining Nanoscale Nano Dwarf 6 9 Nano size: 1 nm = 10 millimeter (mm) = 10 meter (m) nm Combination of atoms or molecules to form objects of nanometer scale Cross section of human hairCarbon nanostructuresImportance of nanoscale • The wavelike 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 selfassembly methods of nature. Importance of nanoscale • Nanoscale 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 optoelectronic applications. •Nanomaterials: 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. •The decorative glaze known as luster. Ruby Red glass pot (entrapped with gold nanoparticles) What’s special with Nano The properties of nanomaterials deviate from those of single crystals or polycrystals (bulk). For example, the fundamental properties like electronic, magnetic, optical, chemical and biological Surface properties: energy levels, electronic structure, and reactivity are different for nano materials. Exhibit size dependent properties, such as lower melting points, higher energy gaps etc. On the Surfaces and interfaces basics: Bulk. In bulk materials, only a Nano. In nanomaterials, large no. relatively small percentage of of atomic features near the atoms will be at or near a interface. surface or interface (like a crystal grain boundary). 15Nanostructured materials • Nanoparticles • Nanowires • Nanotubes • Nanorods • Nanoporous materials • Other structuresBulk and Nanoscale Density of states for 3D, 2D, 1D, 0D showing discretization of energy and discontinuity of DOSElectrons in nanoparticles as particle in a box modelEffects of Nano size • 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 reactivitiesBulk and Nanoscale Bulk (eg. Gold) Nano (eg. Gold) 1. Lustrous–Shiny surface when 1. Vary in appearance depending on polished. size shape of cluster. 2. Malleable–Can be hammered, 2. Are never gold in colour. bent or rolled→any desired shape. 3. Are found in a range of colours. 3. Ductile–Can be drawn out into 4. Are very good catalysts. wires 5. Are not “metals” but are 4. Yellow colour when in a mass semiconductors. 5. Heat electricity conductor 6. Melts at relatively low temperature 6. High densities (940º C). o 7. High melting point (1080 C) 7. Size Shape of the nanoparticles 8. Tough with high tensile strength determines the color. 9. Inertunaffected by air and most 8. For example; Gold particles in reagents glass: 25 nm — Red reflected 50 nm — Green reflected (Unexpected visible properties they are small enough to scatter visible light rather than absorb)Electromagnetic spectrumSize variation Various size of CdSe nanoparticles and their solution. The bulk CdSe is black Room temperature optical absorption spectra of CdSe nanocrystallites dispersed in hexane and ranging in size from ∼12 to 115 ÅNanochemistry Lecture2 Dr Charu Arora, Associate Professor, Department of ChemistryOptical properties of Gold NPs Size, shape, change the optical properties of nano sized gold §4.1.1.1 Gold nanoparticles Red Yellow Size increase Size increase Blue Green Fig 1. Size and shape dependent Orange Brown colors of Au Ag nanoparticles 25Silver : Bulk Nano • In nano size not only the surface area increased the electronic properties are modified. This influence the optical, electrical, catalytic properties • It improve the selectivity in catalysis Silver nanowires Silver nanocubesSilver nanoparticles Change in shape and size shows the difference in the visible spectrum of Ag nanoparticles The scattering or absorption is due to the localized surface plasmon resonanceSPR • Surface plasmon resonance SPR: The collective oscillations of the electron gas at the surface of nanoparticles ( eg. 6s electrons of the conduction band for Au NPs) that is correlated with the electromagnetic field of the incoming light, i.e., the excitation of the coherant oscillation of the conduction band. • SP band provides some information regarding NPs band structure • ( see the notes for detailed information)Silicon Si SiO Nanotubes 2 SiO Nanospheres 2 SiO Nanotubes 2Nano Silicon • Si nanostructures shows visible luminescence because of quantum confinement • Surface modification and change in size of particles influences the luminescence wavelength and intensities Alkyl passivated Si nanoparticlesNano characterization techniques • Spectroscopy – UVVis, Surface enhanced Raman scattering, Xray photoelectron spectroscopy, Nuclear magnetic resonance • Electrical conductivity measurement • Magnetic measurements • Microscopic techniques – Scanning electron microscopy, Transmission electron microscopy, Atomic force microscopy, Scanning tunneling microscopy uses morphology, Surface force measurement, surface roughness, Imaging with atomic level resolution, lattice parameter,Issues • Health hazard The greater specific surface area (surface area per unit weight) may lead to increased rate of absorption through the skin, lungs, or digestive tract and may cause unwanted effects to the lungs as well as other organs. However, the particles must be absorbed in sufficient quantities in order to pose health risks • DNA damage iron oxide , Zinc oxide Titanium dioxide and Carbon nanotubes causes DNA damage at low levels. Copper oxidewas found to be the worst offender, and was the only nanomaterial identified by the researchers as a clear health riskIssues • Nanoparticles in water • Nanoparticles in exhaust gases • Nanoparticles in atmosphereApplicationsNanophotonics • Photonic crystals are new types of optical materials, in which small dielectric cells with the size of optical wavelength (from several 100 nm to several 10 μm) are periodically arranged in two or threedimensions.Nanophotonics Photonic crystal with a diamond lattice.Nanospintronics Gaint magnetoresistance effectNanoelectronics Si nanowire Field effect transistorSingle electron transistors • Uses the coulomb blockade effect of reduced size of nanomaterials • The scaling of such devices down to atomic scaling is expected to replace the customary semiconductor logic or analog devices. Due to the narrowing of the distance to several nanometers between isolated gate from the drain and source, tunneling current surmounts the conventional conduction currents readilyMolecular electronics Nanowire electronicsField effect transistorNanomedicine Drug deliveryQuantum dot imagingEnergy conversion devices • Nanomaterials have obtained considerable applications in electrochemical and solar energy conversion devices • Nanosized electrocatalysts for fuel cell application • Nanostructured materials for Liion batteries • Nanomaterials in electrochemical double Layer supercapacitors
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