1. Research Achievements and Description of Current Activities

Gibbons has worked as a collaborator with other professors at Washington University in all of these projects. He has been investigating the structures of quasicrystals and related complex crystals since 1986 with Kenneth Kelton, also in Physics. They are widely known for the detailed map they made of the localized diffuse scattering in electron diffraction patterns collected from Ti-Mn-Si-O quasicrystals and for their contributions to the theoretical understanding of the diffuse scattering. More recently they were the first researchers to demonstrate the absorption of a large amount of hydrogen by a quasicrystal, in a Ti-Zr-Ni alloy. Ti-Hf-Ni is the subject of a current study of the possibility of an application as a hydrogen-storage, negative electrode for rechargeable batteries. A Ph.D. student in their group recently produced a detailed model of the structure, including hydrogen sites, of the Ti-Zr-Ni quasicrystal.

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 electrical conductivity is 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 measuring x-ray rocking curves for reflections from planes parallel to the substrate. Analysis of widths and of the line shapes provides information about defects in the grown structures and may help us improve performance.

Kelton has identified in his research a number of amorphous metal alloys, some of them quasicrystal forming materials, that we expect will exhibit medium-range order (1.5 nm length scale) or not depending on details of their preparations and heat treatments. Gibbons and Kelton will use a new technique, fluctuation electron microscopy, to detect and characterize the medium range order in samples produced here. This work should provide additional confirmation of Charles Frank's hypothesis that the order in some undercooled liquid metals is icosahedral, for which Kelton published the first experimental proof in 2003. It should also increase our understanding of the devitrification of high-Al metallic glasses into mixed amorphous/nanocrystalline microstructures that have outstanding mechanical properties for structural applications.

Between 2001 and 2007 Gibbons has 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 occurs 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.

Gibbons has years of experience analyzing and interpreting x-ray diffraction, electron diffraction, and electron energy-loss spectroscopy data.

3. Current Collaborations

Dr. Patrick C. Gibbons's Publications

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.