Investigation of beam-induced dynamics in oxide glasses via aXPCS

Michael Legenstein, Bogdan Sepiol

Investigating diffusion in solid state matter has been a long-standing challenge. In recent years a new technique called atomic-scale X-ray Photon Correlation Spectroscopy (aXPCS) has emerged. Its working principle is the same as for the long established Dynamic Light scattering, but with X-rays instead of visible light. The successful realization of an aXPCS experiment was made possible by powerful new X-rays sources like third-generation synchrotrons and free-electron lasers. Ideally, the X-ray beam would only measure internal dynamics and leave the system unperturbed otherwise. However, a recent study has shown that the dynamics in vitreous silica and germanium, measured via aXPCS is proportional to the flux of the beam, while the dynamics in metallic glasses
and single-crystalline Cu90Au10 does not show this behaviour. This indicates that aXPCS does
not only probe dynamics in some materials like oxide glasses, but also induces dynamics. Further investigations of this beam-induced dynamics will be the focus of this thesis.
The thesis begins with a theoretical treatment of aXPCS as well as network glasses in general and oxide glasses in particular. Then the experimental approach and the data evaluation process will be presented in detail.
In the main part the effects of the beam on the dynamics of a wide range of oxide glasses will be investigated. It will be shown that the dynamics in all glasses show a dependence on the photon flux. The dynamics measured at room temperature is proportional to the flux in all glasses, indicating that the dynamics is entirely beam-induced. At temperatures well above room temperature the influence of the beam becomes significantly smaller, hinting at a mixture of beam-induced and internal dynamics.
Furthermore, the characteristics of the induced dynamics will be explored in detail. Finally, the consequences of beam-induced dynamics on future aXPCS experiments will be discussed and some possible mechanism underlying beam-induced dynamics presented.

Dynamics of Condensed Systems
No. of pages
Publication date
Austrian Fields of Science 2012
103008 Experimental physics, 103009 Solid state physics, 103015 Condensed matter, 103018 Materials physics
ASJC Scopus subject areas
Condensed Matter Physics
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