Nanocomposites and nanomaterials
Luminescence and Raman studies of nanostructures 
based on (SiOx–Sm)n  multilayers
 
Michailovska K.V., Dan’ko V.А., Indutnyi I.Z., Shepeliavyi P.E., 
Sopinskyy M.V.
V. Lashkaryov Institute of Semiconductor Physics Natl. Acad. of Sci. of Ukraine. 45 Prospect Nauky, 03028 Kyiv, Ukraine.  
E-mail: danko-va@ukr.net

In recent years Sm-doped materials are widely studied for a variety of optoelectronic application such as optical waveguides, white LEDS, solar cells, X-ray imaging, etc. It is known that the introduction of Sm into oxide glasses contributes to the modification of their structure and properties. As shown by our previous studies, the doping of silicon oxide layers with samarium by co-evaporation of SiO and Sm in vacuum accelerates the formation of silicon nanoparticles (ncs-Si) during annealing of these films in air. In this work, we study the PL and Raman spectra of (SiOx–Sm)n multilayer films obtained by alternate vacuum evaporation of SiO and Sm onto different substrates (c-Si, SiO2 and Al2O3). The number of pairs of nanolayers (n) for the studied samples was 10, the total thickness of the structure was 400 nm. Annealing of the samples was carried out in air in the temperature range of 500–970 ºС for 30 min, resulting in diffusion of Sm into the SiOx layers and thermally stimulated formation of ncs-Si, additionally stimulated by the samarium impurity. The content of Sm in the studied samples was 1.5 wt. %.
The photoluminescence (PL) spectra of (SiOx–Sm)10 films annealed at different temperatures were measured and compared with the spectra of SiOx:Sm samples obtained by coevaporation of SiO and Sm, as well as with SiOx films of the same thickness, annealed under similar conditions. It is shown (SiOx–Sm)10  films exhibit the brightest PL and are more stable with time of storage. In these films, the transition of ncs-Si from the amorphous state to the amorphous-crystalline state begins to manifest itself already at Тan  ≥ 600 ºC. Studies of the Raman spectra of annealed (SiOx–Sm)10 films confirmed the presence of crystalline ncs-Si in the samples and made it possible to estimate the average size of nanocrystals (~3.6 nm). Decomposition of the Raman spectrum into component bands made it possible to detect a band in the region of 495–510 cm–1 and associate it with local variations of the oxygen environment on the ncs-Si–SiOx interface in the SiOx matrix. The mechanisms of participation of Sm in the processes of SiO decomposition and passivation of the surface of formed ncs-Si are discussed.