Modified Solid State Dewetting of Plasmonic Pt NPs by Using In-Pt Bi-Layer System: Improvement on the Surface Morphology and LSPR Properties of Pt NPs

Abstract

The solid state dewetting (SSD) is a useful synthesis technique to fabricate arrays of metallic nanostructures with the diverse size, density, and inter-particle spacing utilizing the solid-state diffusion of atoms below the melting point of elements. However, this technique is limited when the elements utilized possess very low diffusivity such as platinum (Pt), generally yielding poor surface morphologies even at high annealing temperature of 800 °C. In this paper, a clever approach of Pt NP fabrication is demonstrated based on the utilization of sacrificial In layer on sapphire (0001), namely, the modified SSD of In/Pt bilayer system. This approach offers much improved control on the surface morphology of Pt NPs and improved LSPR response. Upon annealing, In atoms can inter-mix with the Pt atoms, consequently yielding the In-Pt alloy and thus can significantly enhance the overall dewetting by increasing the diffusivity. The result is well defined surface morphology of Pt NPs with an improved control at much lower temperature. Subsequently, the desorption of In atoms from the NP matrix occurs through the sublimation, generating nearly pure Pt NPs. These plasmonic Pt NPs exhibit strong absorption bands at the visible region due to the dipolar resonance with the relatively small NPs and along with the gradually improved NP uniformity, the width of extinction peak gradually becomes narrower. The larger Pt NPs demonstrate a slightly broader extinction band in the visible wavelength with the multipolar resonance mode. The significant improvement in the configuration and uniformity of Pt NPs are coherently discussed with the enhanced diffusion, sublimation, Rayleigh-like instability, energy minimization, and equilibrium configuration. The conventional limitation of SDD with the low diffusivity elements can be simply overcome by introducing an intermediate layer with the low surface energy and melting point, which can significantly enhance the dewetting of target system.