Reliable fabrication of high aspect ratio plasmonic nanostructures based on seedless pulsed electrodeposition

Abstract

Strong plasmonic resonance in the visible spectrum requires high aspect ratio metallic resonators with deep subwavelength dimensions, which find applications as part of a cost-effective and practical optics-based sensing platform. Electrodeposition is a highly suitable method for fabricating such structures as it allows deposition of metals with much larger thickness and better morphology than that achieved by physical deposition. Herein are presented an in-depth study of pulsed electrodeposition of a gold film directly onto a transparent substrate without a seed layer and the development of a reliable and efficient fabrication method for high aspect ratio metallic nanostructures with sub-10 nm features. Based on this approach, a low-cost fabrication of sub-100 nm metallic nanostructures is demonstrated with a very high deposition rate (up to 7 nm per pulse), yet with good surface morphology. Specifically, high aspect ratio rotationally symmetric plasmonic nanostructures suitable for a practical sensing platform are realized, exhibiting strong resonances in the visible spectrum with Q factors as high as 10 under unpolarized excitation.