Associate Professor
Senior Staff Scientist 2003-2004, Oak Ridge National Laboratory
Staff Scientist 1994 – 2003, Oak Ridge National Laboratory
Ph. D. Rice University, 1991; B. S. California State University,
Sonoma 1985.
Physical Chemistry
Single-molecule spectroscopy, polymer-based nanoscale photonics.
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Principal Research Interests
Our highly collaborative and interdisciplinary research explores the connection
between structure and optoelectronic function in polymeric and inorganic composite nanostructures. Our experimental approach, termed “Chemical Microscopy,” combines single-molecule imaging and spectroscopy techniques along with scanning probe microscopies such as AFM, to understand details of structure and internal order in macromolecular systems and their relation photonic, or optoelectronic properties.
 In collaboration with Prof. Todd Emrick (Polymer Science & Engineering), we are investigating the photophysics of individual composite quantum dot/conjugated organic nanostructures with the organic species linked directly to the quantum dot surface. Composite blended films of inorganic quantum dots (e.g. CdSe) and conjugated organic polymers (such as polyphenylene vinylene derivatives) have attracted significant recent interest for their unique optoelectronic properties and applications in energy harvesting devices. Our interest has been the connection between the degree of coverage and photophysical properties of the composite nanosystem. Our chemical microscopy studies on these species have revealed a rich and interesting single molecule photophysics that is closely coupled to the degree of surface coverage of the ligand.
 In a separate joint project with the Venkataraman (DV) group at UMass, we are investigating the chemical microscopy of individual chiral molecules. While optical probes of chirality in molecular systems have been in place since the early 1800’s, conventional techniques such as optical rotatory dispersion or circular dichroism necessarily require the participation of a large number of molecules, thus obscuring information on the specific chiroptical signature for an individual molecule. Our research efforts (Hassey, et al., Science, 314, 1437 (2006)) have provided the first observation of the chiroptical response of chiral fluorophores in polymer-supported films and suggest new applications in chiroptical analysis of biofluorophores and novel display technologies.
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| Representative Publications
“Fluorescence Lifetimes and Correlated Photon Statistics from Single Quantum-Dot/Organic Hybrid Nanostructures,” M.Y. Odoi, N.I. Hammer, K. T. Early, K. McCarthy, R. Tangirala, T. Emrick and M.D. Barnes, Nano Letters 7, 2769-2773 (2007).
“On the Origin of Green-Emission Impurities in Polyfluorene-Based OLEDS: Single Molecule Studies of Oligo-Fluorenes and Oligo-Fluorenones,” N. I. Hammer, M. Y. Odoi, H. Rathnayake, P.M. Lahti and M.D. Barnes, Chemical Physics/Physical Chemistry 8, 1481-1486 (2007).
“Intensity Recurrences in the Luminescence Intensity of Individual Quantum-Dot/Organic Hybrid Nanostructures: Experiment and Kinetic Model,” K.T. Early, K. McCarthy, N.I. Hammer, M.Y. Odoi, T. Emrick and M.D. Barnes, Nanotechnology 18, 424027 (2007).
“Probing the Chiroptical Response of a Single Molecule,” R. Hassey, E.J. Swain, N.I. Hammer, D. Venkataraman and M.D. Barnes, Science 314, 1437 (2006).
“Coverage-Mediated Suppression of Blinking in Quantum-Dot/Oligo-Phenylene Vinylene Nanostructures,” N.I. Hammer, K. Early, K. Sill, M. Odoi, T. Emrick and M.D. Barnes, Journal of Physical Chemistry B 110, 14167 (2006) (selected for cover feature on July 27, 2006 issue).
Click Here for a complete list of publications. |
