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

Abstract

Self-organized nanoporous oxide layers (TiO 2 , Al 2 O 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 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/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.

Cubic Silver Nanoparticles Fixed on TiO2 Nanotubes as Simple and Efficient Substrates for Surface Enhanced Raman Scattering

“…The most intense pyridine bands at 1004 and 1034 cm −1 originated from the symmetric ring deformation modes (ν 1 ) and (ν 12 ), respectively [67]. Moreover, SERS spectrum measured using cubic silver nanoparticles deposited on TiO 2 NTs was characterized by other vibrational bands at ~650 cm −1 (ν 6a ), ~1220 cm −1 (ν 9a ), ~1600 cm −1 (ν 8a ), which originated from vibrations of the aromatic ring of pyridine having A1 symmetry [33,67]. Careful inspection of the obtained SERS spectra revealed also, that the two strongest bands had almost identical intensities for the electrochemically activated surface of silver, which agreed with Zuo and Jogodzinski’s work [67].…”

“…Reference SERS-active silver samples (Ag reference) were prepared by the electrochemical roughening of a pure Ag sheet, as in our previous work [33]. The roughening of the silver electrode was carried out in a conventional three-electrode cell with a large platinum sheet as a counter electrode and an Ag/AgCl (0.1 M KCl) electrode as a reference (all potentials are quoted versus this electrode).…”

“…Therefore, the surface roughness, size and shape of the nanoparticles are used to decorate TiO 2 nanotubes influence on the value of enhancement Raman scattering. Achieving the maximum signal during SERS measurements requires optimization of the mentioned parameters [33]. Thus, conventional materials such as rough surfaces of noble metal electrodes obtained in the oxidation reduction cycle, and colloid nanoparticles are increasingly less important due to the development of nanotechnology.…”

Titanium (IV) Oxide Nanotubes in Design of Active SERS Substrates for High Sensitivity Analytical Applications: Effect of Geometrical Factors in Nanotubes and in Ag-n Deposits

“…The SERS enhancement factor (E F ) for the pyridine (Py) probe molecule was successfully estimated using the following formula (1): The hundredfold increase in SERS enhancement shown in Figure 9b is apparently due to a combination of two factors: a change in the specific surface area of the nanotubes with formation voltage [15], and a change in the distribution and size of the Ag nanoparticles with nanotube size [23]. These geometrical factors affect the properties of the silver "nanoresonators" produced on the tops and side walls of the TiO 2 nanotubes.…”

“…The high regularity of the TiO 2 nanotubular structures obtained ensures that the enhancement factors are high reproducible [14][15][16]. The specific morphology of the resulting structures (the large side wall surfaces of the nanotubes grown perpendicular to the substrate) makes it possible to prepare metallic nanograin systems with a large number of gaps between the nanotubes (i.e.…”