Time-resolved X-ray Studies of Kinetics of Metastable Materials

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The use of materials in metastable states is becoming very pervasive in many technological applications. Very often the atomic arrangements in such cases have intermediate-range order somewhat characteristic of crystalline structure but they are not in true thermodynamic equilibrium. The kinetic behavior of metastable structures, and especially their relation to the equilibrium long-range ordered state, is quite poorly understood at present. There has been substantial progress in the theory of non-equilibrium processes using the concepts of kinetic critical phenomena, but little experimental work which probes directly the microscopic mechanisms. We propose a thorough study of this area utilizing powerful ne techniques in time-resolved x-ray diffuse scattering. The research exploits the recent developments in x-ray sources (very brightness synchrotron radiation) and detectors (fast two- dimensional CCDs) which are expected to revolutionize time- resolved studies. The goal of the research is to identify universal features of the kinetics which can be incorporated into a general quantitative description of non-equilibrium structural processes. Two model systems have been chosen for these studies; the research will focus on the rapid thermal annealing of thin- film heterostructures which have important optoelectronic applications, and the growth and relaxation mechanisms of electrochemically deposited dendrites and thin film structures.