Fabrication of SERS-active patterned gold nanoparticle films by electron irradiation and postpyrolysis

An approach to fabricate patterned gold (Au) nanoparticle (NP) films for surface-enhanced Raman scattering (SERS) active substrates is presented on the base of electron irradiation and subsequent pyrolysis of solid precursor films, which is a mixture of hydrogen tetrachloroaurate (HAuCl₄), ethylene glycol, and poly(diallyldimethyl ammonium chloride) (PDDA). Electron irradiation decomposed HAuCl₄ to form Au NP seeds and simultaneously induced cross-link of PDDA. Due to the cross-linking behavior of PDDA under electron irradiation, the precursor film could be patterned by selectively irradiating an electron beam onto the film using a metal mask. Subsequent pyrolysis process resulted in the growth of Au seeds while completely decomposing organic materials, leading to the formation of a patterned film comprising high-purity Au NPs. The size of the Au NPs could be readily controlled from 25 to 92 nm by changing the thickness of the precursor film. The prepared Au NP films exhibited NP size-correlated SERS enhancement factors and had the maximum enhancement factor of 6.6 × 10 ⁵ for thiophenol.