AVS 59th Annual International Symposium and Exhibition
    In Situ Microscopy and Spectroscopy Focus Topic Tuesday Sessions
       Session IS-TuP

Paper IS-TuP3
Determination of the Mechanisms of Photooxidation of CdSe/ZnS Quantum Dots/Shells

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: In Situ Microscopy and Spectroscopy Poster Session
Presenter: L.J. Powell, Carnegie Mellon University
Authors: L.J. Powell, Carnegie Mellon University
S. Saurabh, Carnegie Mellon University
M. Bruchez, Carnegie Mellon University
L.F. Allard, Oak Ridge National Laboratory
L. Qu, Crystalplex Inc.
M. Bootman, Crystalplex Inc.
R.F. Davis, Carnegie Mellon University
Correspondent: Click to Email
Realization of the potential of Quantum Dots (QDs) for biological, energy-efficient lighting and energy harvesting applications requires that their long-term photostability be improved, especially with regards to protection from photooxidation. The overarching objective of this project is the determination of the chemical and physical mechanisms of photooxidation of CdSe QDs. Pittsburgh-based Crystalplex, Inc. is providing 5 nm CdSe QDs for this research. Three integrated in situ characterization techniques are being used to observe changes in QD morphology, optical behavior, and surface chemistry during photooxidation conditions. We are conducting novel microstructural in situ experiments in an aberration-corrected STEM/TEM using a Protochips environmental chamber. Changes in the morphology of single QDs are observed in real-time under O2 and N2 atmospheres up to 1 atm while maintaining atomic resolution. Multiple series of digital micrographs and EDX data are shown. Single-molecule fluorescence microscopy experiments are allowing us to observe real-time changes in the photoluminescence (PL) behavior of single QDs. The QDs are exposed to 1 atm of either pure O2 or an inert gas in an environmental chamber and excited with a 490 nm light source during measurements. Changes in blinking rates and PL intensities are analyzed with respect to the periods of exposure to O2 and light. A series of images and associated statistical analysis are discussed in this poster. In situ XPS at CMU is being used to identify the chemical and bonding states of the reacting species. Analysis of the acquired spectra is also presented. These complementary in situ experiments allow us to assemble a description of the step-by-step photooxidation mechanism.