Optically Active Charge Traps and Chemical Defects in Semiconducting Nanocrystals Probed by Pulsed Optically Detected Magnetic Resonance

ISBN-13: 9783319005898 / Angielski / Twarda / 2013 / 90 str.

Kipp Van Schooten

Opis

Colloidal nanocrystals show much promise as an optoelectronics architecture due to facile control over electronic properties afforded by chemical control of size, shape, and heterostructure. Unfortunately, realizing practical devices has been forestalled by the ubiquitous presence of charge "trap" states which compete with band-edge excitons and result in limited device efficiencies. Little is known about the defining characteristics of these traps, making engineered strategies for their removal difficult.This thesis outlines pulsed optically detected magnetic resonance as a powerful spectroscopy of the chemical and electronic nature of these deleterious states. Counterintuitive for such heavy atom materials, some trap species possess very long spin coherence lifetimes (up to 1.6 us). This quality allows use of the trapped charge's magnetic moment as a local probe of the trap state itself and its local environment. Beyond state characterization, this spectroscopy can demonstrate novel effects in heterostructured nanocrystals, such as spatially-remote readout of spin information and the coherent control of light harvesting yield.

Spis treści

Introduction.- Colloidal Nanocrystals.- Pulsed Optically Detected Magnetic Resonance (PODMR).- Experimental Methods.- Experimental Considerations of PODMR.- Time-Resolved Optical Spectroscopy.- Nanocrystal Materials.- Sample Preparation.- Spin-Dependent Exciton Quenching and Intrinsic Spin Coherence In CDSE/CDS Nanocrystals.- Chapter Synopsis.- Introduction.- Spectrally Selected, Optically Detected Magnetic Resonance.- Coherence Measurements and Novel Effects.- Conclusion.- Supporting Information.- Toward Chemical Fingerprinting of Deep-Level Defects Sites in CDs Nanocrystals by Optically Detected Spin Coherence.- Chapter Synopsis.- Introduction.- Photoluminescence Decay Dynamics Indicating Long Trapping Lifetimes.- Experimental Methods.- Optically Detected Magnetic Resonance vs. Emission Channel.- Increased Dipolar Coupling of Shallow Trap States Associated with the Defect.- Probing Coherence and ESEEM with Optically Detected Hahn Echoes.- Conclusion.- Summary of Work.- Work in Context.- Publications to Date.

O autorze

Kipp van Schooten
Department of Physics and Astronomy
University of Utah
Salt Lake City, UT, 84112
USA

Kipp van Schooten received his Ph.D. in Physics (Condensed Matter focus) from the University of Utah in December 2012. He received the Outstanding Teaching Assistant award each year from 2005 - 2009 for the courses "Intro to Quantum Relativity" and "Solid State Physics II." In 2011, he also received first place for Best Graduate Student Oral Presentation at the University of Utah.

Blurb

Colloidal nanocrystals show much promise as an optoelectronics architecture due to facile control over electronic properties afforded by chemical control of size, shape, and heterostructure. Unfortunately, realizing practical devices has been forestalled by the ubiquitous presence of charge "trap" states which compete with band-edge excitons and result in limited device efficiencies. Little is known about the defining characteristics of these traps, making engineered strategies for their removal difficult.

This thesis outlines pulsed optically detected magnetic resonance as a powerful spectroscopy of the chemical and electronic nature of these deleterious states. Counterintuitive for such heavy atom materials, some trap species possess very long spin coherence lifetimes (up to 1.6 µs). This quality allows use of the trapped charge's magnetic moment as a local probe of the trap state itself and its local environment. Beyond state characterization, this spectroscopy can demonstrate novel effects in heterostructured nanocrystals, such as spatially-remote readout of spin information and the coherent control of light harvesting yield.