Department of Physics , Washington University in St. Louis
366 Compton, Physics Department, CB 1105, Washington University, One Brookings Drive
011 (314) 935-6271
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1. Research Achievements and Description of Current Activities
Characterization of intermediate-range order in amorphous metal alloys by diffraction
Characterization of SLS grown semiconductor nanowhiskers and quantum wires
Development of a high-efficiency photocathode for blue-UV using compositionally modulated, epitaxially grown GaAlN/GaInN heterostructures
Teaching strategies and conceptual change in a professional development program in science for in-service K-8 teachers
Gibbons has worked as a collaborator with other professors at Washington University in all of these projects. He has been consulting since 2002 with Kenneth Kelton, also in Physics, on the interpretation of diffraction data collected from amorphous metal alloys in solid, liquid, and undercooled liquid states. From these data and other measurements inferences can be drawn about intermediate-range order, that beyond first and second neighbors, in the materials. Gibbons continues to consult on the use of fluctuation electron microscopy to obtain additional information about the intermediate-range order in the same amorphous solids.
Since about 1990 Gibbons has collaborated with Bill Buhro, who is in Chemistry. Gibbons trains chemistry students in the use of the transmission electron microscope and works with them and Buhro interpreting the data they obtain. Low temperature growth in solution of 100 nm diameter crystalline semiconductor rods was recognized to be catalyzed by molten metal droplets (In, Ga) when the solid drops were found at the ends of the rods in TEM images. Current work aims to obtain metal spheres a few tens of nm or less in size, monodisperse (all the same size) to use as catalysts for arrays of small diameter, single-crystal, semiconductor rods. These are called quantum wires because their electronic properties are affected by quantum phenomena in this size range.
Since 2001 Gibbons has worked with Dan Leopold and Jim Buckley, both in Physics, to develop and characterize a UV-blue photocathode. The goal, achieved already in prototypes, is a quantum efficiency above 50%, for use in hybrid photomultiplier tubes and imaging detectors in astrophysics experiments requiring high-efficiency detection of Cherenkov or scintillation light. Modern molecular-beam, epitaxial-growth methods are used to prepare compositionally modulated, single-crystal, III-V semiconductor films on transparent, crystalline (sapphire) substrates. Quantum efficiency measurements are made in a chamber attached to the growth chamber, with the structures always in ultra-high vacuum. Gibbons is collaborating in analyzing reflection high-energy electron diffraction data collected in-situ during the growth. Analysis of widths and of the line shapes should provide information about the quality of the grown structures and may help us improve performance.
Between 2001 and 2007 Gibbons supervised Physics graduate students along with colleagues in our Department of Education. They were collecting data about the learning of K-8 teachers enrolled in University College professional development courses in physical science. The first student succeeded in observing the processes by which conceptual change occurred in some of the teachers, and correlating those processes with the teaching strategies employed by the instructors.
2. Unique Facilities and Experimental Capabilities
Gibbons maintains and trains users of the Physics transmission electron microscope. It is a 200 keV JEOL 2000FX with LaB6 filament, a hollow-cone illumination system, Gatan dual tilt room-temperature and heating specimen holders, Gatan 666 parallel electron energy-loss spectrometer, Gatan standard TV rate CCD camera with image intensifier, Gatan high-resolution above-screen CCD camera, and Noran Voyager energy-dispersive x-ray detector. The Gibbons-Kelton research group has sample preparation equipment including two ion mills and a perchloric-acid electrochemical etching system. This equipment is available to qualified users from other research groups.
Kelton’s electrostatic levitator, which allows undercooling of liquid metal alloys because there is no container with heterogeneous nucleation sites for crystallization, and which can be moved to an x-ray diffraction beam line at the Advanced Photon Source, is one of only a few and produces very useful data of high quality.
Gibbons has years of experience analyzing and interpreting x-ray diffraction, electron diffraction, and electron energy-loss spectroscopy data.
3. Current Collaborations
* Dr. Phyllis Balcerzak, Science Outreach, Washington University
* Associate Professor James H. Buckley, Physics, Washington University
* Professor William E. Buhro, Chemistry, Washington University
* Professor Kenneth F. Kelton, Physics, Washington University
* Research Associate Professor Daniel Leopold, Physics, Washington University
* Ms. Ann P. McMahon, Science Outreach, Washington University
* Mr. John F. Wiegers, Science Outreach, Washington University
Dr. Gibbons is a member of the Center for Materials Innovation and of Science Outreach
Gibbons received his Ph.D. in physics from Harvard in 1971; advisor Norman Ramsey. He served as instructor and assistant professor in physics at Princeton from 1971 to 1976; supervisor Steve Schnatterly. He came to Washington University as assistant professor of physics in 1976, and has more recently served as associate professor and professor of physics.
Gibbons has taught introductory physics courses for science majors and for non-science majors, upper level undergraduate courses for physics majors, and graduate-level physics courses. He also teaches hands-on physical science for in-service elementary teachers. He has served as a consultant in the school districts of University City and Riverview Gardens.
Gibbons's research in experimental physics has evolved from atomic physics (Harvard) to solid-state physics (Princeton and Washington University) and more recently to materials physics.