4211930
Descrição
FlashCards por emmalmillar, atualizado more than 1 year ago
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Criado por emmalmillar
quase 9 anos atrás
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| Questão | Responda |
| 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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