High-Quality Ultrathin Gold Layers with an APTMS Adhesion for Optimal Performance of Surface Plasmon Polariton-Based Devices

Abstract

A low absorption adhesion layer plays the crucial role for both localizing and propagating surface plasmons when ultra-thin gold is used. To date, the most popular adhesion layers are metallic, namely Cr and Ti. However, to the best of our knowledge, the influence of these adhesion layers on the behaviour of propagating plasmons modes has not been thoroughly investigated nor reported in literature. It is therefore important to study the role of these few to several nanometres thick adhesion layers on the propagating plasmons since it may affect the performance of plasmonic devices, in particular when the Au layer thickness is not much thicker than the adhesion layers. We experimentally compared the performances of the ultra-thin gold films in order to show the pivotal role of adhesion layers on highly localized propagating plasmonic modes, using Cr and APTMS (3-Aminopropyl)trimethoxysilane adhesion layers and without any adhesion layer. We show that the gold films with the APTMS adhesion layer have the lowest surface roughness, and the short range surface plasmon polaritons (SR-SPPs) supported on the Au surface exhibit properties close to the theoretical calculations, considering an ideal gold film.