MATERIALS SCIENCE COLLOQUIUM

Refreshments will be served at 10:45 a.m.

ABSTRACT: This talk describes unprecedented bathochromic shifts (up to 970 meV) of the optical bandgaps of CdS, CdSe, and PbS quantum dots (QDs) upon adsorption of an organic ligand, phenyldithiocarbamate (PTC), and the use of PTC to map the quantum confinement of specific charge carriers within the QDs as a function of their radius. For a given QD material and physical radius, R, the magnitude of the increase in apparent excitonic radius (DR) upon delocalization by PTC directly reflects the degree of quantum confinement of one or both charge carriers. The plots of DR vs. R for CdSe and CdS show that exciton delocalization by PTC occurs specifically through the excitonic hole. Furthermore, the plot for CdSe, which spans a range of R over multiple confinement regimes for the hole, identifies the radius (R ~ 1.9 nm) at which the hole transitions between regimes of strong and intermediate confinement. The talk will also describe the dependence of DR on the energy of the HOMO of PTC, and the effect of PTC on the photoluminescence of the QDs. This demonstration of ligand-induced delocalization of a specific charge carrier is a first step toward eliminating current-limiting resistive interfaces at organic-inorganic junctions within solid-state hybrid devices.