Events at Physics |
Events During the Week of August 31st through September 7th, 2008
Monday, September 1st, 2008
- No events scheduled
Tuesday, September 2nd, 2008
- Chaos & Complex Systems Seminar
- Complex nanostructures driven by screw-dislocation nanowire growth
- Time: 12:05 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Song Jin, UW Department of Chemistry
- Abstract: I will discuss some complex "Christmas Tree" like nanowire structures spontaneously formed through chemical reactions. These fascinating nanostructures demonstrate a ?new? nanowire formation mechanism that is completely different from the well-known metal catalyzed vapor-liquid-solid (VLS) mechanism. The screw component of an axial dislocation provides the self-perpetuating steps to enable 1-dimensional crystal growth, unlike previously understood mechanisms that require metal catalysts. This mechanism was found in hierarchical nanostructures of lead sulfide (PbS) nanowires resembling ?pine trees? that were synthesized via chemical vapor deposition. Structural characterization reveals a screw-like dislocation in the nanowire trunks with helically rotating epitaxial branch nanowires. The rotating trunks and branches are the consequence of the Eshelby twist of screw dislocations. We suggest that screw dislocation growth is overlooked and underappreciated in modern literature on one-dimensional nanomaterials. The proposed nanowire growth mechanism will be general to many materials and enable more complex nanostructures to be synthesized in the future to enable diverse applications.
Wednesday, September 3rd, 2008
- No events scheduled
Thursday, September 4th, 2008
- R. G. Herb Condensed Matter Seminar
- Multi-scale modeling of nano-devices
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Paul von Allmen, Jet Propulsion Lab (Pasadena, CA)
- Abstract: Paul von Allmen and Trinh Vo
Seungwon Lee, Fabiano Oyafuso and Gian Franco Sacco
NASA - Jet Propulsion Laboratory
California Institute of Technology
The modeling of nano-scale devices requires simulation capabilities at length scales that span many orders of magnitude, precluding the use of a single modeling approach. At one end, the electrodes have significant features at the micron scale, and at the other end, the electronic wavefunctions are defined at the sub-nanometer scale. We have been integrating a hierarchy of approaches, for the calculation of the electronic structure and the lattice dynamics, into a package that can for example compute the effect of varying the electrode potential on atomic-level properties in realistic device structures. The electrostatic potential is obtained from a finite element solution of Poisson's equation. The charge density is described at 4 levels of decreasing scale: the semiclassical approach, the effective mass approximation, the parameterized tight-binding method, and first principles density functional theory. The lattice dynamics is described with valence force fields for large systems and density function theory at finer levels. The coupling with the electromagnetic field is described with a density matrix approach or the Keldysh formalism. This talk will give an overview of the methods available at JPL and give a few illustrative examples, such as the modeling of spin qubits in Si/SiGe quantum dots, and transport properties in Si and SiGe nanowires. - Host: Joynt
Friday, September 5th, 2008
- No events scheduled