| Abstract [eng] |
The periodic metal nanostructures used for the research in the field of plasmonics are usually produced by a lithography or other relatively slow surface processing methods. The laser direct writing is now increasingly being used for the accurate and fast production of the large arrays of the nanostructures with different morphology. The lattices excite hybrid lattice plasmon polaritons, the resonance of which is very sensitive to the changes of the environment refractive index. The aim of this work was to investigate the dependence of the back-side resonance of the periodic gold nanostructure gratings on the radiation, sample and lattice parameters, measure the quality of the resonances and to determine the applicability of such structures in the fields of plasmonic sensor and surface enhanced Raman spectroscopy. The reflectance spectra of the samples were measured to determine the influence of the azimuthal angle, light polarization, morphology of the structures, gold and glass thicknesses, incident angle and lattice period on the resonance wavelength and quality. When illuminated from the back-side, the resonances are shifted to the longer wavelengths, compared to the direct illumination of the gold lattice from air, and some of the resonances have a quality factor above 100. The influence of the polarization, incident angle and period are the same as for front-side illumination – the different resonant modes are achieved in different polarizations, which red-shift with increasing period and change the wavelength by the increase of the angle of incidence. In contrast to the front-side results, the structure morphology does not influence the place in the spectrum of the back-side resonance and only affects the quality and the shape of it. The use of a thicker gold coating slightly increases the overall intensity of the reflection spectra, while the use of a thinner glass increases the depth of the resonant peak. A theoretical model of diffractive resonant wavelength was developed and it was in good agreement with practically obtained results. For the investigation of practical applications of the lattices, the samples were stored in a mercaptobenzoic acid to form a monolayer. Measuring the reflectance spectra of the sample with the attached molecules, a spectral red-shift was observed, which proved the suitability for the application as sensors, and the sensitivity exceeded 100 nm/RIU. The lattices also enhanced Raman scattering, with the strongest scattering being observed in the cone and antenna arrays with the enhancement factor of 106. The results show that the back-side excited resonances have higher quality factor that are suitable for the applications as plasmonic sensors and in Raman spectroscopy. |
