Fabrication of Au-Ag nanorod SERS substrates by co-sputtering technique and dealloying with selective chemical etching

Abstract

Surface enhanced Raman scattering (SERS) is a surface sensitive technique that is attractive for molecular detection. SERS performance has nanometallic structure dependence however fabrication of a substrate with high sensitivity, uniformity, reproducibility and stability is still one of the most active topics in SERS research. In this study, we report the fabrication of Au-Ag dealloyed nanorod SERS substrates via a co-sputtering technique by oblique angle deposition (OAD) followed by selective chemical etching. Substrates were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, water contact angle, ultraviolet–visible spectrometry, X-ray diffraction, acid-base titration and Raman spectroscopy. Results showed that the surface roughness increases on the dealloyed substrate compared to the alloy substrate and more gold atoms are available on the surface of the dealloyed substrates for 4-MBA absorption which played a vital role in enhancing the SERS effect. The optimal SERS substrate was achieved by etching in methanol, hydrogen peroxide, and ammonium hydroxide solution for 40 s. The Au-Ag dealloyed substrates exhibited increased SERS enhancement factor in the range of 1.5x106. Long-term stability of the optimal dealloyed substrates was observed over a month of storage time under ambient conditions, superior to the Au-Ag alloyed and Ag only nanorod substrates. In addition, the Au-Ag dealloyed substrates demonstrated uniformity and reproducibility with an acceptable relative standard deviation.