Free and open to the public
Math and Physics Building, Room 318
"Time-domain ab initio studies of quantum dots and carbon nanotubes"
Device miniaturization requires an understanding of the dynamical response of materials on the nanometer scale. A great deal of experimental and theoretical work has been devoted to characterizing the excitation,charge, spin, and vibrational dynamics in a variety of novel materials,including carbon nanotubes, quantum dots, conducting polymers, inorganicsemiconductors and molecular chromophores. We have developedstate-of-the-art non-adiabatic molecular dynamics techniques andimplemented them within time-dependent density functional theory in orderto model the ultrafast photoinduced processes in these materials at theatomistic level, and in real time.
The electron-phonon interactions in carbon nanotubes (CNT) determine theresponse times of optical switches and logic gates, the extent of heatingand energy loss in CNT wires and field-effect transistors, and even asuperconductivity mechanism. Our ab initio studies of CNTs directly mimicthe experimental data and reveal a number of unexpected features,including the fast intrinsic intraband relaxation and electron-holerecombination, the importance of defects, the dependence of the relaxationrate on the excitation energy and intensity, and a detailed understandingof the role of active phonon modes.
Quantum dots (QD) are quasi-zero dimensional structures with a uniquecombination of molecular and bulk properties. As a result, QDs exhibit newphysical properties such as carrier multiplication, which has thepotential to greatly increase the efficiency of solar cells. Theelectron-phonon and Auger relaxation in QDs compete with carriermultiplication. Our detailed studies of the competing processes in PbSeQDs rationalize why carrier multiplication was first observed in thismaterial.
Pizza and soda will be served