Date of Award
Doctor of Philosophy (PhD)
Gilbert R. Hoy
Gary E. Copeland
Since 1985 nuclear-resonant scattering, and in particular nuclear forward-scattering, of synchrotron radiation has been observed in a select few Mossbauer isotopes including: 57Fe, 119Sn, 169Tm. For the first time, nuclear forward-scattering from the 9.4 keV Mossbauer level in 83Kr has been observed. A large resonance effect, comparable to that in 57Fe, has been observed in a variety of systems containing Kr including bulk crystals and physisorbed Kr-on-exfoliated graphite. Previous nuclear-resonant scattering experiments using synchrotron radiation have consisted of demonstration experiments. Nuclear forward-scattering from Kr has been applied to study the lattice dynamics of near-monolayer Kr-on-graphite by measurement of the probability for recoil-free scattering, i.e., Lamb-Mossbauer factor, (fLM) as a function of both relative coverage on the substrate and sample temperature. This represents the first practical application of the nuclear forward-scattering technique to a previously unsolved physical problem.
It was found that fLM of the physisorbed Kr displays a coverage-dependent behavior, indicating a change of the in-plane fLM due to neighbor-neighbor interactions in the layer. At low coverages, the slope of fLM with temperature is reminiscent of anharmonic behavior in the bulk, while at near-monolayer coverages, the slope of fLM with temperature is like a harmonic 3-D solid. A measurement of fLm at low temperatures through the commensurate-incommensurate transition of Kr-on-graphite shows a dramatic decrease and slow recovery in the transition region. This behavior is shown to be consistent with a simple calculation of the interaction energy of the incommensurate layer.
The nuclear forward-scattering technique is shown to be a powerful tool, complementary to conventional x-ray diffraction measurements, as the time-resolved resonant scattering is free from any non-resonant graphite background and independent of the static structure of the system.
Johnson, David E..
"Nuclear Forward-Scattering of Synchrotron Radiation From Krypton: First Observation and Application to the Study of Lattice Dynamics in Near-Monolayer Krypton-on-Graphite"
(1995). Doctor of Philosophy (PhD), Dissertation, Physics, Old Dominion University, DOI: 10.25777/tp0z-wg54