TiO2 and Al2O3 nanoporous oxide layers decorated with silver nanoparticles—active substrates for SERS measurements

Abstract

Self-organized nanoporous oxide layers (TiO2, Al2O3) exhibiting specific properties, obtained by anodic oxidation at a constant voltage in neutral electrolyte, may serve as attractive SERS substrates for investigating the interactions between an adsorbate and adsorbent, or as a stable platform for detecting various organic compounds. This paper presents the influence of the size of the nanotubes/nanopores and the structure of the porous oxide layers on the SERS enhancement factor, E F. We used pyridine and mercaptobenzoic acid as probe molecules, since they have a large cross-section for Raman scattering. To characterize the morphology and structure of the oxide layer substrates, before and after vacuum vapor deposition of silver nanoparticles, we applied scanning electron microscopy, X-ray diffraction and surface analytical techniques: AES, XPS and SERS. The results obtained show that for the same amount of Ag (0.02 mg/cm2) the size of the nanopores significantly affects the E F, which reaches, at a properly chosen nanopore size, distinctly higher values than that characteristic of a standard silver surface roughened by electrochemical cycling, i.e. E F > 106. The new Ag/MeO x –NT composites layer, ensure a good reproducibility of the SERS measurements and exhibit stability over a limited period of time.