Nanoplasmonics and surface enhanced spectroscopy

Effect of technological parameters on properties of Ag plasmonic structures prepared on garnet substrates  
M. Kushlyk1, V. Tsiumra1, 2, L.-I. Bulyk1, 2, Ya. Zhydachevskyy2, 3, V. Haiduchok3, 4, I.I. Syvorotka3, 4, D. Sugak3, 4, A. Suchocki2, 5
1 Ivan Franko National University of Lviv, 107 Tarnavskoho str., Lviv 79017, Ukraine  
2 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw 02-668, Poland 
3 Lviv Polytechnic National University, 12 Bandera str., Lviv 79646, Ukraine
4 SRC „Carat“, 202 Stryjska str., Lviv 79031, Ukraine
5Institute of Physics Kazimierz Wielki University, 11 Weyssenhoffa str., Bydgoszcz 85-072, Poland 
E-mail: kushlykmarik@gmail.com

The structures with metallic NPs have high extinction coefficients when frequencies of the incident electromagnetic field coincide with those of electron oscillations. At the same time, frequency and width of the surface plasmon resonance (SPR) absorption peak depend on size and shape of the particles as well as on dielectric functions of metal and the environment. Particles of metals such as gold, silver and copper have high absorption in visible region. PL intensity for a radiating dipole near the Au particle may be up to 100 ÷ 150 times higher and for Ag NP – up to 103. That is why silver is the material mostly used for increasing efficiency of plasmonic structures in the near-UV or visible spectral range. 
Here, technological aspects of preparation of silver nanostructures and their plasmonic properties are studied. The plasmonic structures were prepared on single-crystalline YAG and GGG garnet as well as amorphous glass substrates by the magnetron sputtering technique. A thermal annealing process controlled a nucleation and growth of Ag nanoparticles. Two broad absorption bands peaked at 350-370 nm and 440-650 nm were observed due to quadrupole and dipole modes, respectively, of Ag nanoparticles SPR. Changes of the positions, intensity and width of these absorption bands related to the nanoparticles size, density and their shapes are presented. Degradation of the plasmonic structures at ambient conditions, which is revealed as diminishing of the plasmonic absorption bands and associated with sulphidation of Ag nanoparticles in the natural environment, was studied in details. Theoretical simulations of the sulphidation process modelled as a coating of Ag nanoparticles with silver sulphide (Ag2S) film confirm the experimentally observed diminishing of SPR.