Particle size and shell thickness dependence of the light intensity enhancement in the cap layers of Ag, Au, Al and SiO2@TiO2 core-shell nanostructures

Abstract

We present a systematic study of the light intensity enhancement in the shell layers of half burrried Ag, Au, Al and SiO2 spherical nanoparticles capped with TiO2. We calculated the light intensity profiles near these structures when they are illuminated by a UV light at 380 nm. The calculations cover the particle-size range between 20 and 180 nm, and the cap thickness range between 6 and 80 nm. Our data is the first report on the intensity enhancement in the shell layers of TiO2-capped Al nanoparticles and Al@TiO2 core-shell nanostructures. We obtain, in the cap layers, an average intensity enhancement of similar to 3.7, similar to 6.1, similar to 2.4 and similar to 2.7 for a cap thickness of similar to 30nm above Ag, Al, Au and SiO2 particles. Taking into account the increase in the active surface area, these numbers can be multiplied by a factor of two, for each capped-nanoparticle system. The optimal Ag, Au, Al and SiO2-particle sizes for a 30-nm cap-thickness are found to be 120 nm, 80 nm, 140 nm, and 80 nm. While half-buried and capped-nanoparticle systems resemble the typical core-shell nanoparticles, the intensity enhancements are not equivalent. We compare the intensity increases in these two systems at the optimal sizes for Ag and Al particles for a 30-nm shell thickness.