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2012 Chemistry Newsletter
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The UO Chemistry Department is now accepting applications for Fall 2013. Our priority application deadline is December 15, 2012. Completed late applications will be accepted through January 5, 2013. Instructions and our application can be accessed on our Apply Page
M.S. (Physics), Moscow Institute of Physics and Technology, 1999 (Yu. E. Lozovik). Ph.D. (Chemistry), UC Irvine, 2007 (Wilson Ho). Postdoctoral: Brookhaven National Laboratory, 2007-2010 (Peter W. Sutter). Honors and Awards: Goldhaber Distinguished Fellowship, Brookhaven National Laboratory, 2008; E.K.C. Lee Award, UC Irvine, 2005; Chancellor's award for academic excellence, Moscow Institute of Physics and Technology, 1999.
Professor George Nazin's group is developing novel scanning probe techniques for atomic-resolution spectroscopic studies of physics and chemistry in molecular and nanoscale materials.
The Nazin group will investigate the connection between the chemical structure and properties of nanoscale materials and devices. We are particularly interested in real-space experimental approaches that provide spectroscopic information on the atomic and molecular scales. At the initial stage of this work we will construct a state-of-the-art Ultra-High Vacuum Scanning Tunneling Microscope (STM), an instrument that will allow direct imaging and spectroscopic measurements of individual atoms and molecules (Fig. 1), as well as construction of artificial nanostructures in-situ (Fig. 2).
Fig. 1: (A) The topography of a surface of interest is determined by using the quantum-mechanical tunneling of electrons between the surface and an atomically-sharp metallic tip located within a few Angstroms above the surface. This tunneling electron current is sensitive to the surface structure on the atomic scale. (B) Energy-diagram of electronic states in an STM junction with a molecule on the sample surface. On the diagram, electrons from occupied states (shown in blue) in the tip tunnel into the Lowest Unoccupied Molecular Orbiltal (LUMO) of the molecule. Current through individual molecules is enhanced by the presence of molecular electronic and vibrational states, which produce distinct features in the current-voltage characteristics. This is useful for identification of the local chemical structure. (C) By injecting high-energy electrons into individual adsorbates, one can induce and observe fluorescence-like radiation that contains spectroscopic information about individual adsorbates.
Fig. 2: STM image (bottom) with a schematic (top) of a model molecular junction consisting of two gold atomic chains and a CuPc molecule bridging the gap between the two chains. This molecular junction was assembled by manipulating the CuPc molecule and individual gold atoms with an STM tip. In this work (done in the group of Professor Wilson Ho at UC Irvine) the molecular junction was used to visualize the chemistry of molecular electronic devices.
The new STM will allow us to gain unique insights into the properties of novel nanoscale materials. Indeed, at the nanoscale, the properties of materials become strongly size-dependent and sensitive to the surface chemistry. One striking example of this is the gold atomic wires seen in Fig. 2: instead of being metallic, as one would expect a gold wire to be, these wires have a semiconductor-like electronic structure, which changes with addition (or extraction) of a single gold atom. These gold wires effectively are all-surface (no bulk), and adsorption of even a single molecule on such a wire (the molecule doesn't have to be CuPc) can disrupt the one-dimensional particle-in-a box electronic states in such chains. Similar effects are also important in other nanoscale objects, such as quantum dots, nanowires, nanotubes and thin films, with dramatic consequences for their electronic structure, charge and energy transport, optical properties, etc. The powerful combination of atomic-scale imaging, spectroscopy and manipulation afforded by the new STM will allow us to gain unique insights into the relationship between the chemical structure and properties of novel nanoscale materials. Further, by combining STM experiments with characterization of devices made using such nanomaterials, we will be able to evaluate how the spectroscopic properties determined using STM methods relate to the device behavior, which is essential for laying out the groundwork required for a rational design of future nanoscale devices.
Some of the future research directions are described below:
1) Nanoscale inorganic semiconductors: We will explore possible strategies for surface passivation and functionalization of nano-structured inorganic semiconductors using self-assembled organic monolayers, with potential applications in such areas as electronic memory elements, and photovoltaic cells.
2) Organic semiconductors: Research in organic semiconductors will be aimed at understanding the impacts of the molecular structure, composition and packing in molecular solids on the processes associated with energy and charge transfer, which are central to the operation of electronic and photovoltaic devices based on organic semiconductors.
3) Graphene: Graphene is a one-atom-thick planar sheet of carbon atoms arranged in a hexagonal lattice. This simple chemical structure gives rise to many properties that make graphene a very unique type of material. For example, electrons in graphene are described by a chiral Dirac-like (rather than Shrodinger) equation, which leads to highly unusual charge transport properties. Further, graphene shows very high intrinsic charge carrier mobility and thermal conductivity, which makes it an attractive candidate for electronic applications beyond the silicon roadmap. Using STM, our group will investigate the impact of surface chemistry on the charge-transport properties of graphene, and explore possibilities for creating new two-dimensional graphene-based materials with properties tuned via surface chemical modification. Our research is at the intersection of several disciplines, including surface science, molecular spectroscopy, organic chemistry, as well as solid state chemistry and physics. Students working in our group will have the opportunity to participate in construction of novel instrumentation and learn such techniques as ultra high vacuum technology, scanning probe microscopy, nanoscale device fabrication and optical spectroscopy.
G.V. Nazin, Y. Zhang, L. Zhang, E. Sutter, and P. Sutter, "Visualization of charge transport through Landau levels in graphene," Nature Physics, Advance online publication, August (2010).
S.W. Wu, N. Ogawa, and G.V. Nazin, W. Ho, "Conductance hysteresis and switching in a single-molecule junction," J. Phys. Chem. C 112, 5241-5244 (2008).
G.V. Nazin, S.W. Wu, and W. Ho, "Tunneling rates in electron transport through double barrier molecular junctions in a scanning tunneling microscope," Proc. Natl. Acad. Sci. 102, 8832-8837 (2005).
G.V. Nazin, X.H. Qiu, and W. Ho, "Charging and interaction of individual impurities in a monolayer organic crystal," Phys. Rev. Lett. 95 166103 (2005).
G.V. Nazin, X.H. Qiu, and W. Ho, "Vibrational spectroscopy of individual doping centers in a monolayer organic crystal," J. Chem. Phys. 122, 181105 (2005).
X.H. Qiu, G.V. Nazin, and W. Ho, "Vibronic states in single molecule electron transport," Phys. Rev. Lett. 92, 206102 (2004).
X.H. Qiu, G.V. Nazin, and W. Ho, "Mechanisms of reversible conformational transitions in a single molecule," Phys. Rev. Lett. 93, 196806 (2004).
G.V. Nazin, X.H. Qiu, and W. Ho, "Visualization and spectroscopy of a metal-molecule-metal bridge," Science 302, 77-81 (2003).
X.H. Qiu, G.V. Nazin, and W. Ho, "Vibrationally resolved fluorescence excited with submolecular precision," Science 299, 542-546 (2003).
G.V. Nazin, X.H. Qiu, and W. Ho, "Atomic engineering of photon emission with a scanning tunneling microscope," Phys. Rev. Lett. 90 216110 (2003).
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