Conformal covering and optical response of pulsed laser deposited bidimensional Ag nanoparticle arrays

We demonstrate successful nanometric conformal coverage by pulsed laser deposition ( PLD) of Ag nanoparticle ( NP) arrays with a transparent amorphous Al2O3 layer. The Ag NPs-arrays are formed by a bimodal distribution of well separated spheroidal Ag NPs with an average in-plane diameter of 40 or 90 nm and a maximum height of similar to 70 nm. The cover layer induces no relevant alteration of the morphology and organization of the underlying Ag NPs-arrays. The conformal nature of the Al2O3 cover layer is confirmed by its surface topography that shows the presence of characteristic nanodomes, with sizes determined by those of the underlying Ag NPs. The distinctive tapered shape of the nanodomes is related to the angular dependence with respect to the NPs surface normal of the deposition rate and the self-sputtering induced by energetic Al+ ions present in the laser generated plasma. The presence of the amorphous Al2O3 cover layer red-shifts the characteristic dipolar and quadrupolar Surface Plasmon Resonances of Ag NPs and increases the total and diffuse reflectance of the NPs arrays.