Paul grew up in Grinnell, a small town in Iowa home (not coincidentally) to Grinnell College. He holds a B.A. in physics from Oberlin College, and a M.S. and a Ph.D. in physics from the University of Illinois at Urbana-Champaign, where he worked with Murray Gibson. Half his graduate research work was performed at the NEC Research Institute with Mike Treacy. After a post-doc with David Muller at Bell Labs, Paul joined the MS&E faculty at UW Madison in November of 2002.
Paul’s research focus is characterization of materials structure using high-energy electron scattering in the TEM. The existence of good lenses for electrons and their large scattering cross sections means that meaningful scattering can be obtained from as little as 1 nm3 of material. This leads to a host of different signals and techniques, including Bragg diffraction, high-order Laue zone diffraction, and various spectroscopic techniques such as electron energy loss and characteristic x-ray emission.
Paul has worked primarily on diffraction-based techniques. Much of his work has been on developing and applying fluctuation electron microscopy, starting as a graduate student with the technique’s inventors, Murray Gibson and Mike Treacy. Fluctuation microscopy is an experimental technique with unique access to nanometer-scale structural order in amorphous materials. This new information comes from studying the spatial fluctuations in Bragg angular range scattering with nanometer resolution. This work, and the fluctuation microscopy technique, are described extensively elsewhere on this site.
Paul has also worked with Z-contrast STEM imaging, in which a wide angular range of high-angle scattering is collected as a function of the position of a small electron probe. The resulting images show strong elemental sensitivity, and can be of atomic resolution. With David Muller, Paul demonstrated the first Z-contrast STEM images with quantifiable contrast from individual impurity atoms inside a crystal lattice. He also explored the importance of probe channeling in Z-contrast STEM images of zone axis crystals. In a more recent extension of this work, Paul has explored the influence of channeling on three dimensional imaging by optical sectioning in a spherical-aberration corrected STEM. In related work with John Einspahr, Paul explored the optics and influence of channeling on optical sectioning in a novel TEM/STEM configuration, the confocal STEM.
Paul’s current work his group at UW involves application of fluctuation microscopy to marginal and bulk amorphous metals and chalcogenide glasses, and microstructural / microchemical characterization of superconducting MgB2, all of which are described in greater detail elsewhere.