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2013 Chemistry Newsletter
The Department of Chemistry Newsletter is now available.
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2013 Beckman Scholars Program
The UO Chemistry Department will be awarding prestigious Beckman Research Scholarships to qualifying undergraduate research students. 2013 Beckman Scholars Information
Research in the Lonergan group blends synthesis, physical measurement and rational design to better understand or discover interesting electrical and electrochemical phenomena in solid-state systems. We are particularly interested in using chemistry to control interfacial electron transfer processes, which can depend on applied bias in complex, nonlinear, and often asymmetric ways. Practical impetus for our work comes from the importance of electroactive interfaces to many devices for the useful manipulation of electrical energy including solar cells, batteries, fuel cells, and logic gates.
One focus area is the family of polymers known as conjugated ionomers. These materials are defined by a -conjugated backbone and covalently bound ionic functionality. A prototypical example is given by the polyacetylene ionomer shown below:
This polymer is one of a much broader set of materials synthesized in our laboratory using ring-opening metathesis polymerization.
Conjugated ionomers are unusual materials. Unlike conventional polymers, they are electrically active. Furthermore, they blend the properties of typical electronic conductors, such as graphite, with ionic conductors, such as brine. Electrical conductivity comes from the ability of the -conjugated backbone to support the addition or removal of electrons, and ionic conductivity comes from the presence of ionic functionality.
The mixed ionic/electronic nature of conjugated ionomers results in extremely rich solid-state electrochemical behavior, and it is at the heart of a number of important discoveries within the Lonergan group. These include new mechanisms of unidirectional charge transport, new approaches to modulating the conductivity of organic conductors, and the first example of a conjugated polymer pn homojunction – a crucial building block for semiconductor electronics.
The above discoveries raise many fundamental issues now being addressed regarding the interplay between ionic and electronic processes in solid-state mixed ionic/electronic conductors; the relation of interfacial charging to redox chemistry in nanoscale systems that blur these two processes; and the use of ions to engineer regions of space charge and subsequently control interfacial charge transfer. They also drive efforts toward even more sophisticated polymer structures where multiple features are built into a single polymer through copolymerization or other means. These more sophisticated structures target molecular-level analogues to the types of junctions that form the basis for modern semiconductor electronics.
A second important area being explored in the group deals with the electrical and electrochemical properties of nanostructures. Charge transport and photoinduced charge separation are being studied in a variety of systems. Two examples are blends of semiconductor nanoparticles with conjugated polymers and planar interfaces with well-defined lateral nanostructure defined using electron beam lithography.
The Lonergan group is made up of researchers with diverse backgrounds ranging from synthetic organic chemistry to applied physics. Students in the group draw on classic topics from chemistry (physical, organic, and inorganic), physics and more specialized areas such as polymer chemistry, electrochemistry, and semiconductor device physics. Major tools used by the group include a wide variety of electrical and electrochemical methods, organic and polymer chemistry, techniques for molecular and polymer characterization, numerical simulation, and electron beams for lithography and imaging.
F. Lin, E.M. Walker, M.C. Lonergan, "Photochemical Doping of an Adaptive Mix- Conducting p-n Junction", J. Phys. Chem. Lett. 1, 720 (2010).
S.G. Robinson, D.H. Johnston, Christopher D. Weber, Mark C. Lonergan, "Polyelectrolyte- Mediated Electrochemical Fabrication of a Polyacetylene p-n Junction", Chem. of Mater. 22, 241 (2010).
Stephen G. Robinson, Mark C. Lonergan and Reginald H. Mitchell, "Oligothiophene Functionalized Dimethyldihydropyrenes II: Electrochemical and Conductive Properties", J. Org. Chem. 74, 6606 (2009).
I.S. Moody, A.R. Stonas, and M.C. Lonergan, "PbS Nanocrystals Functionalized with a Short-Chain, Ionic, Dithiol Ligand", J. Phys. Chem C. 112, 19383 (2008).
S. W. Boettcher, N. C. Strandwitz, M. Schierhorn, N. Lock, M. C. Lonergan, and G. D. Stucky, "Tunable Electronic Interfaces between Bulk Inorganic Semiconductors and Ligand-Stabilized Inorganic Nanoparticle Assemblies", Nature Materials 6, 592 (2007).
F. Lin and M.C. Lonergan, "Gate electrode processes in an electrolyte-gated transistor: Non-Faradaically versus Faradaically coupled conductivity modulation of a polyacetylene ionomer", Applied Physics Letters 88, 133507 (2006).
C.H.W. Cheng, F. Lin, M.C. Lonergan, "Charge transport in a mixed ionically/electronically conducting, cationic, polyacetylene ionomer between ion blocking electrodes", J. Phys. Chem. B. 109, 10168-10178 (2005).
M.C. Lonergan, "Charge transport at conjugated polymer-inorganic semiconductor and conjugated polymer-metal interfaces", Ann. Rev. of Phys. Chem. 55, 257-298 (2004).
C.H.W. Cheng and M.C. Lonergan, "A conjugated polymer pn junction", J. Am. Chem. Soc. 126, 10536-10537 (2004).
C.H.W. Cheng, S. W. Boettcher, D.H. Johnston, and M.C. Lonergan, "Unidirectional Current in a Polyacetylene Hetero-ionic Junction", J. Am. Chem. Soc. 126, 8666-8667 (2004).
C. Daniels-Hafer, M. Jang, S.W. Boettcher, R. Danner, and M.C. Lonergan, "Electrochemical Tuning of Charge Transport at the interface between Indium Phosphide and a Polypyrrole-phosphomolybdate Hybrid", J. Phys. Chem. B 106, 1622-1636 (2002).
M.C. Lonergan, C.H. Cheng, B.L. Langsdorf, X. Zhou, "Electrochemical Characterization of Polyacetyelene Ionomers, and Polyelectrolyte Mediated Electrochemistry Toward Interfaces Between Dissimilarly Doped Conjugated Polymers", J. Am. Chem. Soc. 124, 690-701(2002).
B. L. Langsdorf, X. Zhou, M. C. Lonergan, "Kinetic Study of the Ring Opening Metathesis Polymerization of Ionically Functionalized Cyclooctatetraenes," Macromolecules 34, 2450-2458 (2001).
M. C. Lonergan and F. E. Jones, "Calculation of Transmission Coefficients at Non-Ideal Semiconductor Interfaces Characterized by a Spatial Distribution of Barrier Heights," J. Chem. Phys. 115, 443-455 (2001).
F. E. Jones, B. P.Wood, J.A. Myers, C. Daniels-Hafer, and M. C. Lonergan, "Current transport and the Role of Barrier Inhomogeneities at the High Barrier n-InP | Poly(pyrrole) Interface," J. Appl. Phys. 86, 6431-6441 (1999)
M. C. Lonergan, "A Tunable Semiconductor Diode Based on an Inorganic Semiconductor | Conjugated Polymer Interface," Science 278, 2103-2106 (1997).
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