On the importance of optical contacts in gold hybrid structures for enhancement of localized surface plasmon resonance sensing

Gold/polymer hybrid structures consisting of gold-coated dielectric particles resting on a thin gold mirror layer are investigated in view of their optical sensitivity toward molecular adsorption. Three different methods, i.e., metal evaporation, sputtering, and wet chemistry, are used to prepare metal coatings of different roughness and different extent to which the dielectric cores are engulfed by the metal. Further, the presence of contacts between the dielectric cores is varied. As a well-understood organic monolayer system, the sensitivity of the different hybrid structures toward adsorption of octadecanethiol is studied from ethanolic solution. Thereby, it is found that besides surface roughness, core-core contacts are important for the layers' optical response, which is governed by surface plasmon effects. The system prepared by means of wet chemistry that allows for core-core contacts achieves an about 4 fold higher sensitivity toward molecular adsorption as compared with that prepared by evaporation.