Thermally Structured Gold Films for SERS Substrates—Patterns With and Without Solid-state Dewetting

Abstract

This paper presents an experimental study on the manufacturing process of surface enhanced Raman scattering (SERS) substrates obtained by the thermal structuring of gold films. Three such samples were fabricated by depositing gold on glass substrates, inside an ultra high vacuum (UHV) installation. The UHV facility also included a sample heater, an argon ion gun and an atomic force microscope (AFM). As the efficiency of a SERS substrate is optimum for a particular value of the horizontal granularity of the metallic film, which is linked to the laser wavelength used to probe the sample, we aimed to gradually increase the horizontal granularity, through several stages of thermally induced structuring, so to get as close as possible to this optimum value. The horizontal granularity of the gold film was expressed in terms of the surface correlation length, calculated for a 20% reference threshold of the surface correlation function, which we denoted by SCL20. This parameter can be measured from the AFM images of the gold films, which are taken at various stages in the fabrication process, and it gives meaningful values for the horizontal granularity, irrespective of the fact that the thermally induced pattern exhibits solid-state dewetting or not. Therefore, this parameter offers a useful unique measuring criterion for the horizontal granularity, as it can be applied to both continuous and discontinuous films. After fabrication, the SERS performance of each sample was measured and compared with that of a commercial sample, which had a paper based active region impregnated with gold nanoparticles.