X-ray Intensity Fluctuation Spectroscopy (XIFS) is an ideal technique to perform measurements on the dynamics of fluctuations in condensed matter systems. Over the past few years, XIFS has been used in several studies of dynamics in both hard condensed matter and soft condensed matter equilibrium systems. Its extension to study the dynamics of non-equilibrium systems is currently under way. In this thesis, we present the first applications of XIFS to study dynamics during a first order phase transition with nonconserved order parameter (model A). The order-disorder phase transition in the binary alloy Cu3Au has been chosen as a case study for such a non-equilibrium process and has been studied using XIFS. Our experiments have confirmed the theoretical predictions for the scaling laws describing the evolution of the density-density correlation functions, which are measured by the autocorrelation function of the scattered intensity. The covariance of the scattered intensity was found to be proportional with scaling functions with natural variables delta t = |t1 - t 2| and t¯ = t1+t22 , as predicted by theory. However, some significant early-time deviations from this scaling picture have been observed and are currently under investigations. / In order to study non-equilibrium processes in condensed matter systems, a very precise and fast temperature control system is often required. In order to trigger the particular process under study and to obtain meaningful experimental data, the temperature has to change by hundreds of degrees in very short times, while completely avoiding any over/under shooting. To achieve this, we designed and implemented a computer-controlled temperature tracking system which combines standard Proportional-Integral-Derivative (PID) feedback, thermal modeling and finite difference thermal calculations (feedforward) and Kalman filtering of the temperature readings in order to reduce the noise. The resulting Kalman-Predictive-Proportional-Integral-Derivative (KPPID) algorithm allows us to obtain accurate control, to minimize the response time and to avoid over/under shooting, even in systems with inherent noisy temperature readings and time delays. The KPPID temperature controller was successfully implemented at the Advanced Photon Source at Argonne National Laboratories and was used to perform the coherent X-ray diffraction experiments described in this thesis.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84245 |
| Date | January 2003 |
| Creators | Fluerasu, Andrei |
| Contributors | Sutton, Mark (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002101835, proquestno: AAINQ98253, Theses scanned by UMI/ProQuest. |
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