Nanotechnology

Description

Masters Physics Flashcards on Nanotechnology, created by emmalmillar on 11/12/2015.
emmalmillar
Flashcards by emmalmillar, updated more than 1 year ago
emmalmillar
Created by emmalmillar almost 9 years ago
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Resource summary

Question Answer
What is nanoscale science and physics? The science/physics of phenomena occurring at a scale of 1 to 100nm.
What is nanotechnology? The understanding and control of matter at dimensions of 1-100nm.
What is the nano length scale between? Atomic and bulk behaviour
What is a quantum dot? 3D confinement
What is a quantum wire? 2D confinement
What is a quantum well? 1D confinement
Draw picture and D(E) graph for quantum dot, wire and well.
What can be determined by the particle in a box model? New electronic and optical properties determined by size, shape and composition. The size of the box must be similar to the de Broglie wavelength of the particle.
What are colloidal quantum dots? The photoluminescence of the quantum dot (CdTe nanocrystal) is exclusively determined by the size. This makes then tunable absorbers/emitters in imaging.
Semiconductor nanowires can be used as ...heterojunction solar cells, as are a good interconnector
Semiconductor quantum well can be used in... laser diodes, due to it's 2D structure with tuneable optical and electronic properties.
What are metal nanoparticles? -They exhibit collective oscillations of conduction band electrons -"plasmons" -large enhancement and localisation of EM fields at optical frequencies -applications in spectroscopy and microscopy
Why are nanostructures different from the bulk? -quantum confinement -large surface-to-volume ratio -small size
Why are nanostructures different from the bulk? Quantum Confinement... QC reduces the number of vibrational electronic states to discrete levels, this causes band gap widening and changes in optical, electronic and electrical properties.
Why are nanostructures different from the bulk? Large surface-to-volume ratios... enhanced chemical reactivity lower melting points
Why are nanostructures different from the bulk? small size.. Structural relaxations more likely to be defect free resulting in enhanced mechanical properties -> stronger materials improved electrical properties-> better conductivity Particle comparable to bloch length in magnetic materials single domain per particle
How many atoms are there in a 5nm diameter nanocrystal? Assume lattice constant (d)=0.5nm cubic lattice Sphere volume= pi/6 d cubed =1/2 125 nm3 unit cell is 125E-3 nm3 Divide 500 atoms
What is driving nanotechnology? Science ie curiousity Technological Imperatives ie sustainable energy Revolutionary Promises ie targeted medicine
What is Moore's Law? Number of transistors on a chip doubles every 18-24 months. Will reach molecular scale by 2020, when quantum effects will become important. Leakage Currents & Heating.
Electrostatic Interactions Occurs between atomic and molecular ions Is responsible for binding in ionic solids (NaCl) Mediated by coulomb interaction
Covalent Bonds Directing bonding between atoms mediated by valence electrons H2+ ion
Van-der-waals Force The residual attractive of repulsive forces between molecules that do no arise from covalent bonding of electrostatic interaction. Molecules with permanent dipole moments Hydrogen Bonding
Dipole-Dipole The potential for interaction between two permanent dipoles This allows rotation and averaging over Boltzmann distribution Hydrogen Bonds are dipole-dipole interactions
Permanent dipole-induced dipole interaction The Debye Force Permanent dipole induces dipole in polarisable molecule and interacts with it
Induced dipole-induced dipole interaction The London Dispersion Force In nearby polarizable molecules, electron densities show correlations that induce dipoles which interact
Describe and draw the Lennard-Jonas potenial. This combines the vdw force with short-range Pauli repulsion
Metallic Bonding Conduction band electrons in metals are delocalised between ionic cores. This shields core repulsion and provides attractive potential. Cu
What is the density of states? The number of available states per energy interval.
Give two examples of what D(E) defines: the metallic conductivity and the specific heat.
What is electron transport? In a free electron gas, electrons are accelerated by the electric and magnetic fields according to the lorentz field.
What happens in transport through a single channel? There is no scattering, so the conductivity will be quantised.
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