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Report No.

Dynamics of silver photo-diffusion into Ge-chalcogenide films; Time-resolved neutron reflectometry

Sakaguchi, Yoshifumi*; Asaoka, Hidehito ; Uozumi, Yuki; Kawakita, Yukinobu ; Ito, Takayoshi*; Kubota, Masato ; Yamazaki, Dai ; Soyama, Kazuhiko ; Ailavajhala, M.*; Latif, M. R.*; Wolf, K.*; Mitkova, M.*; Skoda, M. W. A.*

We report the results of time-resolved neutron reflectivity measurements of Ag/a- Ge$$_{20}$$S$$_{80}$$/Si and a- Ge$$_{40}$$Se$$_{60}$$/Ag/ Si films taken while the films are exposed to visible light. Silver diffuses into an amorphous (a-) chalcogenide layer while visible light illuminates Ag/a-chalcogenide films. Neutron reflectometry is a suitable technique probing time evolution of the multi-layer structure without damaging the sample by the probe beam itself. It was found from the measurements of Ag/a-Ge$$_{20}$$S$$_{80}$$/Si films that a relatively stable Ag-rich phase in the reaction layer is first formed, and then, slower diffusion occurs at the interface between Ag-rich and Ag-poor layers. This result is in contrast to the previously reported model of silver diffusion that suggests a mechanism involving progression of the diffusion front. From the measurements of a-Ge$$_{40}$$Se$$_{60}$$/Ag/ Si films, we found enormous changes in the neutron reflectivity profile, including loss of total reflection region, with continuous illumination even after forming one homogeneous layer, which was about 60 min after starting illumination. At this stage, clear off-specular scattering was observed by a linear detector and a surface roughness was observed with naked eyes.



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