Nanoplasmonics and surface enhanced spectroscopy

On the effect of surface plasmon polaritons on photostimulated diffusion of silver into As2S3 film 
Indutnyi I. Z., Mynko V. I., Sopinskyy M. V., and Lytvyn P. M.
V. Lashkaryov Institute of Semiconductor Physics Natl. Acad. of Sci. of Ukraine. 45 Prospect Nauky, 03028 Kyiv, Ukraine.  
E-mail: indutnyy@isp.kiev.ua 

The photostimulated diffusion of Ag into thin films of chalcogenide glasses (ChG) had been investigated and still being studied by many scientists, not only from the practical point of view, but also to determine the mechanism of the phenomenon. In previous studies, it was established that the first and decisive stage of this phenomenon is the absorption of photoactive light in the ChG at the ChG–Ag interface, and that the Ag diffusion intensity depends on the light intensity at this interface. Therefore, increasing the intensity of photoactive light at the interface between silver and chalcogenide can stimulate the diffusion of the metal and significantly increase the sensitivity of ChG –Ag structures. One way to significantly increase the intensity of an electromagnetic field at the metal–dielectric interface is to excite surface plasmon-polaritons (SPP), which are characterized by the localization of the electromagnetic field just at the boundary with the dielectric. This determined the goal of this work, that is, to determine a correlation between the excitation of surface plasmon polaritons at the chalcogenide glass (here As2S3)–silver interface and photodiffusion of the metal into the As2S3 layer.
The substrate for investigated samples was a diffraction grating with a period of 899 nm, made by interference photolithography, on which a two-layer Ag-As2S3 structure was deposited. Photostimulated changes in such structure were registered by measuring the kinetics and the angular dependences of the specular reflection of the 632.8 nm wavelength p-polarized light (He-Ne laser). Specifically, the shift of the plasmon minimum of specular reflection as well as changes in its depth and half-width with exposure had been recorded.  It was found that the process of photostimulated diffusion of silver into the chalcogenide layer significantly accelerates at its initial stage (by 3–4 times) when the SPP is excited at the Ag-As2S3 interface during irradiation. Thus, it promotes the increase in photosensitivity of such a structure - when irradiated at an angle corresponding to the excitation of the SPP, the entire photodiffusion process completes much faster.