Conformal dielectric covering of 2D Ag nanoparticle arrays by Pulsed laser deposition for enhanced optical response

E-MRS Spring Meeting 2018, Symposium X "Photon-assisted synthesis and processing of materials in nano-microscale. European Materials Research society, 18-22 of June. Strasbourg – France (2018) https://www.european-mrs.com/photon-assisted-synthesis-and-processing-materials-nano-microscale-emrsConformal coatings are essential to develop microelectronic and photonic structures since they not only protect them but they also enable additional functionalities, for example as absorbers. In this work we demonstrate the nanometric conformal growth of a pulsed laser deposited (PLD) thin transparent amorphous Al2O3 (a-Al2O3) cover layer on 2D Ag nanoparticle (NP) arrays that show a strong localized surface plasmon resonance (LSPR) response. The 2D Ag NP array was formed by depositing a percolated Ag film by PLD in vacuum, followed by a thermal annealing in air at 300 ºC to allow the formation of well separated Ag semispheroidal NPs by dewetting (average in-plane diameter 100 nm, maximum height ~70 nm). Finally the a-Al2O3 cover film (~70 nm thick) was deposited on top of them. SEM analysis shows that the cover film induces no relevant alteration of the morphology and organization of the 2D Ag NP arrays. The surface topography of the a-Al2O3 film shows the presence of nanodomes, with sizes determined by those of the underlying Ag NPs, therefore confirming its conformal nature. The presence of the cover film shifts the characteristic dipolar and quadrupolar LSPRs of the Ag NPs to lower energy values (by about 0.5 eV), and increases the overall specular and diffuse reflectance. The possibility of achieving near-Brewster conditions with this structure and its possible application for light-harvesting and optical sensing will be discussed