TiO_2 and Al_2O_3 nanoporous oxide layers decorated with silver nanoparticles-active substrates for SERS measurements

摘要

Self-organized nanoporous oxide layers (TiO_2, Al_2O_3) 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 nanotubesanopores 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/cm~2) 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>10~6. 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.