Solid state dewetting of Ag/Pt bilayers for the stronger localized surface plasmon resonance (LSPR) properties: The dynamic control of surface morphology and elemental composition of AgPt and Pt nanostructures by the auxiliary Ag layer

The modification and control of localized surface plasmon resonance (LSPR) properties of metallic nanoparticles (NPs) has become a vigorous research focus in various fields due to its wide range of applicability in various applications, which can be achieved by the control of surface morphology and elemental composition. In this paper, various configurations and compositions of AgPt and Pt NPs are demonstrated by the solid state dewetting using an auxiliary Ag layer on sapphire (0001) along with their strong dynamic LSPR properties. By the systematic control of Ag/Pt bilayer thickness and temperature, the interconnected AgPt nanoclusters at low temperature (<600 °C) and well-isolated pure Pt NPs at higher temperature (>650 °C) are obtained based on the enhanced diffusion, alloying, surface energy minimization and Ag sublimation. A strong LSPR response in the UV and VIS region is exhibited by the AgPt and Pt NPs depending on the alteration of size, shape, uniformity and elemental compositions. In particular, the AgPt NPs show the stronger plasmonic responses and it gradually attenuates with the sublimation of Ag atoms which results in the development of Pt NPs. In comparison with the previous study on the pure Pt NPs on sapphire, the Pt NPs in this study are significantly improved in terms of shape, size and spacing, whose LSPR responses are much stronger and dynamic. The auxiliary diffusion enhancement by Ag atoms leads to the rapid dewetting of AgPt NPs while the Ag sublimation assists the evolution of well-developed Pt NPs due to the vacancy creation and removal of material during mass transport. The tunability of surface morphologies and LSPR properties of AgPt and Pt NPs are systematically demonstrated by the methodical control of Ag/Pt bilayer thickness.