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Phase-change alloys constitute the basis for a widening collection of storage technologies both optical and electrical. These uses of phase-change alloys are characterized by switching material properties either by laser irradiation or by an electric current on the nanosecond time scale. Considering the conflicting requirements for high-speed switching, yet long term data storage integrity, a deeper understanding of the switching processes in these materials is essential for insightful application development. We have used synchrotron-based time-resolved X-ray absorption fine structure spectroscopy (XAFS), a technique equally suitable for amorphous and crystalline phases to elaborate details in structural changes in the phase-change process on a sub-nanosecond time scale using optical pump/X-ray probe techniques. In this work, we present initial results of sub-nanosecond laser excitation of the laser-reamorphized state of Ge2Sb2Te5. The technique is general and can be applied to a wide variety of nanoscale structures.

The cation extraction process in the bilayer cyanide film with an epitaxial interface, Na0.84-y Co2+[Fe y 3+Fe1-y 2+(CN)6]0.713.8H2O (NCF71)/Na1.60-x (Co x 3+Co1-x 2+)[Fe2+(CN)6]0.902.8H2O (NCF90), was investigated by depth-resolved X-ray absorption spectroscopy. Assuming stepwise depth (z) distributions of Co3+ and Fe3+, we estimated the step depths, d Co and d Fe, and concentrations, δCo and δFe, of the respective ions against the average quantity (δav) of cation extraction. The Na+ extraction was found to be dominant in the NCF90 surface layer, consistent with the lower redox potential in the NCF90 layer. We found that the magnitude of d Fe (∼600 nm) is much deeper than the actual depth (d = 200 nm) of the NCF71/NCF90 interface, and interpreted the behavior in terms of the redox interaction in the vicinity of the interface.

The total-reflection X-ray spectroscopic technique was applied to an interfacial species at the liquid-liquid interface. The XAFS spectrum of bromide ions at the heptane-water interface was successfully obtained in the fluorescence mode. A slight change in the spectra was observed in the presence of the cationic surfactants, dimethyldilaurylammonium and stearyltrimethylammonium ions. This suggested that the hydrated structure of bromide ions attracted by the cationic surfactants at the heptane-water interface is different from neat interfaces or bulk aqueous phases.

X-ray reflection measurement of a water surface was demonstrated using recently developed liquid interface reflectometer at SPring-8. The reflectometer equipped with two-dimensional hybrid pixel array detector, PILATUS, achieved x-ray reflectivity towards 10-9 with the integration time at each angle of only 1 sec, having enormous potential for quick measurements.

A total-reflection X-ray absorption fine structure (TR-XAFS) method was successfully extended to the liquid-liquid interface that allowed the investigation of the 'buried' interface by fluorescence detection. The first X-ray absorption spectrum at the Br K-edge for bromide ions concentrated at the heptane-water interface was observed in the presence of dimethyldipalmitylammonium ions.