Date: Tuesday, February 9, 2016
Time: 11:00 am
Speaker: Oleg Prezhdo, USC
Title: Quantum Dots – Artificial Atoms, Large Molecules or Small Pieces of Bulk? Insights from Time-Domain Ab Initio Studies
Location: 67-3111 Chemla Room
Quantum dots (QD) are quasi-zero dimensional structures with a unique combination of solid-state and atom-like properties. Unlike bulk or molecular materials, QD properties can be modified continuously by changing QD shape and size. Often, the bulk and molecular viewpoints contradict each other. The molecular view suggests strong electron-hole and charge-phonon interactions, and slow energy relaxation due to mismatch between electronic energy gaps and phonon frequencies. The bulk view advocates that the kinetic energy of quantum confinement is greater than electron-hole interactions, that charge-phonon coupling is weak, and that the relaxation through quasi-continuous bands is rapid. QDs exhibit new physical phenomena. The phonon bottleneck to electron energy relaxation and generation of multiple excitons can improve efficiencies of solar energy devices. The enhanced electron-hole interactions and high densities of states enable highly-efficient Auger-type processes, including a new electron transfer mechanism, which are impossible in both bulk and molecules. The observed QD properties are complicated by presence of ligands, dopants, defects and other atomistic features. Our state-of-the-art non-adiabatic molecular dynamics techniques, implemented within time- dependent density-functional-theory, allow us to model QDs at the atomistic level and in time-domain, providing a unifying description of quantum dynamics on the nanoscale.