Associate Professor of Physics
"My research interests include two main thrusts, magnetic characterization of materials and using magnetic resonance techniques to investigate defects in semiconductors.
Magnetic susceptibility measurements taken over a range of magnetic fields and temperatures can allow one to determine the spin state of metal centers as well as characterize any intra-molecular and even inter-molecular magnetic interactions. In collaboration with inorganic chemists at Knox and elsewhere, my lab investigates the magnetic properties of novel compounds. These investigations lend themselves very well to undergraduate participation. On the chemistry side, Knox students make many of the compounds we characterize. Physics research students, working closely with me, learn how to collect magnetic susceptibility data on a state of the art SQUID magnetometer and analyze it.
Additionally, I have had a continuing interest in bistable defects in semiconductors. This fascinating class of defects is associated with some unusual properties like persistent photoconductivity and persistent photorefractivity. For example, CdTe:Ga is a poor conductor, but under illumination its conductivity increases by several orders of magnitude (photoconductivity). At low temperatures (below 100 K) the enhanced conductivity brought on by illumination will persist even after the illumination is removed. This interesting behavior is attributed to the dopant Ga atoms. These Ga atoms trap electrons in deep energy levels, but light is able to 'free' them. I am interested in using Nuclear Quadrupole Double Resonance Spectroscopy to probe the local environment of these defects."
Years at Knox: 2005 to present
Ph.D., Physics, 1999, Oregon State University.
M.S., Physics, 1995, Oregon State University.
B.S., Physics, 1993, Truman State University.
Introductory physics, modern physics, classical dynamics, electrodynamics, statistical mechanics, and physics of sports.
Selected Professional Accomplishments
*Denotes Knox Student, †Denote's Knox Faculty
"The Crystal Structure and Magnetic Susceptibility of Tetrakis-(μ2-phenylacetato-O,O′)-bis(caprolactam-O)copper(II)." Co-authored with Kraig A. Wheeler, *Edward J. Dale, *Travis Helgren and †Thomas W. Clayton. Journal of Chemical Crystallography (2011).
"Nuclear Quadrupole Double Resonance Spectrometer with Magnetic Property Measurement System Direct Current Superconducting Quantum Interference Device Detector and Automatic Tuning." Co-authored with Edmund P. Day. Review of Scientific Instruments (2011).
"Nuclear Spin-lattice Relaxation by Optically Bistable Defects in Cd2:In." Co-authored with W.W. Warren, Jr., and A.I. Ryskin. Physical Review B 65 (2002).
"Zeeman-tuned Slowing of Rubidium Using σ and σ- Polarized Light." Co-authored with S.K. Mayer, N.S. Minarik, and D.H. McIntyre. Optics Communications 210 (2002): 259-270.
"NMR Study of Bistable Defects Under in situ Illumination." Co-authored with J.K. Furdyna, A.I. Ryskin, and W.W. Warren, Jr. Physica B 273-274 (1999): 852-855.
"Pulsed NQDR with SQUID Detection: A New Spectroscopic Technique for the Study of Quadrupole Nuclei in Proteins." With E.D. Coulter, D.M. Kurtz, and E.P. Day. International Conference on Biological Inorganic Chemistry, Florence, Italy, 2001.
"NMR Study of Bistable Defects Under in situ Illumination." With J.K. Furdnyna, A.I. Ryskin, and W.W. Warren, Jr. International Conference on Defects in Semiconductors, Berkeley, California, 1999.
"NMR Studies of Spin-Lattice Relaxation Mechanisms in CdTe:Ga and CD1-xMnxTe:Ga." American Physics Society Meeting, Kansas City, Missouri, 1998.
Campus & Community Involvement
Instructor, Knox College for Kids.
Site Coordinator, Worldwide Youth in Science and Engineering (WYSE) sectional competition.
Assistant Men's Basketball Coach, Knox College.
Coach, MathCounts, Churchill Jr. High.
Member, Galesburg Community Chorus.
What Students Say
"Professor Shroyer makes the physics department feel like home. Being a physics major requires a lot of late nights and, apparently, so does being a professor. Professor Shroyer is there for his students at nearly any hour of the day, into the night, and sometimes into the very early morning. He is always willing to help, and will do so with great pride. He loves his job, and takes great care to make sure his students are proud of everything they do."
-Sophie Townsend, Physics and Secondary Education Major
"Professor Shroyer is one of the most intense men I've ever met. He loves Physics, and he loves being able to teach the subject to his students. He wants everyone in his class to understand the material to the best of his or her ability and works hard to be there for any student willing to come to him for help."
-Kasandara Sullivan, Physics Major and Mathematics and Latin Minor
"Dr. Shroyer is a very approachable and enthusiastic professor. In class, his enthusiasm wears off on the students, and he is always willing to help students both in and out of class."
-Emma Lorenzen, Physics and Chemistry Major