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American Chemical Society, ACS Nano, 8(8), p. 7858-7869, 2014

DOI: 10.1021/nn5014319

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Fast, Simple, Combinatorial Routes to the Fabrication of Reusable, Plasmonically Active Gold Nanostructures by Interferometric Lithography of Self-Assembled Monolayers

This paper is available in a repository.
This paper is available in a repository.

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Abstract

We describe a fast, simple method for the fabrication of re-usable, robust gold nanostructures over macroscopic (cm2) areas. A wide range of nanostructure morphologies is accessible in a combinatorial fashion. Self-assembled monolayers (SAMs) of alkylthiolates on chromium-primed polycrystalline gold films are patterned using a Lloyd's mirror interferometer and etched using mercaptoethylamine in ethanol in a rapid process that does not require access to clean-room facilities. The use of a Cr adhesion layer facilitates the cleaning of specimens by immersion in piranha solution, enabling their repeated re-use without significant change in their absorbance spectra over two years. A library of 200 different nanostructures was prepared, and found to exhibit a range of optical behavior. Annealing yielded structures with a uniformly high degree of crystallinity that exhibited strong plasmon bands. Using a combinatorial approach, correlations were established between the pre-annealing morphologies (determined by the fabrication conditions) and the post-annealing optical properties that enabled specimens to be prepared "to order" with a selected localized surface plasmon resonance. The refractive index sensitivity of gold nanostructures formed in this way was found to correlate closely with measurements reported for structures fabricated by other methods. Strong enhancements were observed in the Raman spectra of tetra-tert-butyl unsubstituted phthalocyanine (TTB-H2Pc). The shift in the position of the plasmon band after site-specific attachment of histidine-tagged green fluorescent protein (His-GFP) and bacteriochlorophyll a was measured for a range of nanostructured films, enabling the rapid identification of the one that yielded the largest shift. This approach offers a simple route to the production of durable, reusable, macroscopic arrays of gold nanostructures with precisely controllable morphologies.