[MOS] March 4, 2014, Emily Weiss, Northwestern University

[Zina M Queen]

Seminar on

Modern Optics and Spectroscopy

 

The Optical properties of strongly coupled Quantum Dot-Molecule Systems

 

Emily Weiss,

Northwestern University 

Tuesday, March 4, 2014

12:00 – 1:00 p.m.

This talk describes the mechanisms by which organic surfactants – in particular phenyldithiocarbamate (PTC) and its derivatives – couple electronically to the delocalized states of semiconductor quantum dots (QDs). This coupling reduces the confinement energies of excitonic carriers, and, in the case of PTC, the optical bandgap of metal chalcogenide QDs by up to 1 eV by selectively delocalizing the excitonic hole. The reduction of confinement energy for the hole is enabled by the creation of interfacial electronic states near the valence band edge of the QD. The PTC case illuminates the general minimal requirements for surfactants to achieve observable bathochromic or hypsochromic shifts of the optical bandgap of QDs: frontier orbitals with energies near the relevant semiconductor band-edge, the correct symmetry to mix with the orbitals of the relevant band, and an adsorption geometry that permits spatial overlap between the orbitals of the ligand and those of the relevant band. NMR measurements indicate that the magnitude of exciton delocalization, as measured by the effective increase in excitonic radius, DR, increases linearly with surface coverage of PTC and substituted PTCs. Transient absorption measurements on complexes of QDs and zinc-porphyrins show that bis-PTC molecules are effective cross-linking ligands for enhancing yields of electron transfer within donor-acceptor complexes.

 

Grier Room, MIT Bldg 34-401

Refreshments served after the lecture


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