My primary activities have focused on involving undergraduate students in fundamental research and projects related to physics teaching or engineering.
Recently, several undergraduate students and other collaborators have been working with me to investigate two materials—chromium-doped VO2 thin films and amorphous V2O5. Pure vanadium dioxide is known to undergo transition from an insulator to a metal at 340 K; chromium-doped VO2 also experiences this transition in the same temperature regime. Our work focuses on monitoring changes in the chromium EPR resonance as a function of temperature in the vicinity of the transition temperature. Our results show that this EPR line intensity undergoes a factor-of-four decrease as the system changes from insulator to metal. Tentatively, this change is attributed to the onset of a soft (phonon) mode accompanying distortion of the lattice.
EPR spectra for the V2O5 system exhibit a single broad resonance down to 120 K, in contrast to well-resolved spectra obtained by previous workers. In addition, signal intensities increase more rapidly (with decreasing temperature) than predicted by Curie’s law. Both of these observations can be explained tentatively by proposing the existence of superparamagnetism SP in the V2O5 system. Experiments proposed here will further investigate whether or not SP exists in this system. In addition, EPR spectra will be evaluated to determine details of the paramagnetic center’s local environment. In particular, EPR analyses will reveal the oxidation state of the vanadium ion, the degree to which the 3d electron is delocalized, and time scales for local magnetic interactions. The goal of the work is to understand amorphous V2O5 on a fundamental level in order to predict materials properties when the system is doped or co-deposited in films.
My most recent published work focused on investigating solid-acid systems (such as CsHSO4) that undergo superprotonic phase transitions. Such transitions are characterized by dramatic (four-order-of-magnitude) increases in proton conductivity at the superprotonic transition temperature. Our experiments measured proton NMR relaxation times (T1 and T2), in an effort to characterize this transition. These results showed that both T1 and T2 reveal transformation to a regime of rapid hydrogen motions above the transition temperature. An activation energy barrier to diffusion in the temperature regime approaching the transition also was obtained. Overall, the work shows that NMR spectroscopy is useful for detecting and characterizing superprotonic phase transitions.
Two students also worked with me on developing a classroom project to determine coefficients of restitution COR’s for sport balls. Initially, students are introduced to a technique for determining COR’s in which time of flight for a bouncing object is used to extract COR’s. Subsequently, students formulate questions related to COR’s and perform experiments to answer those questions.
