Multi-fold plasmon-enhanced photoluminescence of a-C:H thin films

Abstract

The regularities study of a-C:H film photoluminescence (PL) enhancement by localized surface plasmon resonance (LSPR) in hybrid structures with nanogranulated Ag film was the main aim of this work. We have compared the PL spectra of two thin-film hybrid structures in which the a-C:H optical gap was 2.7 eV and 0.4 eV. The a-C:H films with the thickness of ~50 nm were deposited on quartz substrates using the chemical vapor deposition of toluene vapor in glow discharge plasma. The nanogranulated silver film by 10 nm thickness was deposited on all a-C:H film by the thermal evaporation method at the same time. The optical density spectra and the surface morphology of Ag nanoparticles (NPs) by AFM as well as the PL spectra of a-C:H in the hybrid structures at the visible range and room temperature were obtained. It has been shown that PL intensity of wide-gap a-C:H in the hybrid structure increased fourfold but the narrow-gap film – sevenfold against the intensity of initial films at excitation wavelength 405 nm. The intensity of dipole and quadrupole mode peaks increased in the optical density spectra after annealing of the hybrid structures at 200 °C. This fact was connected with the form and size changes of Ag NPs. The blue shift of PL maximum to 498 nm and the twentyfold enhancement of PL intensity of the hybrid structure with the narrow-gap a-C:H was observed after annealing. The mechanism of plasmon-enhanced of a-C:H PL in hybrid structures with Ag NPs was discussed. Obtained results can find practice applications in both light-emitting devices and biosensor chip.