Raman investigations of TiO2 nanotube substrates covered with thin Ag or Cu deposits

A tubular array of TiO2 nanotubes on Ti matrix was used as a support for Ag or Cu sputter-deposited layers intended for surface-enhanced Raman scattering (SERS) investigations. The composite samples of Ag/TiO2 - nanotube/Ti and Cu/TiO2 - nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) [and scanning Auger microscopy (SAM)] to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured after it had been adsorbed on the TiO2 - nanotube/Ti substrates covered with thin Ag or Cu deposit as well as on the bulk electrochemically roughened Ag or Cu reference substrates. It was found that the SERS spectra measured for pyridine adsorbed on the bulk silver substrate were significantly different than the spectra measured on the TiO2 - nanotube/Ti substrates covered the Ag layer. The spectra measured for pyridine adsorbed on the Ag/TiO2 - nanotube/Ti suggest that on the surface of such a composite substrate there are many Lewis acidic sites. Spectra typical for pyridine adsorbed on acidic sites were observed even after deposition of a relatively thick silver layer (e.g. an Ag layer with an average thickness of 80 nm) on the TiO2 - nanotube/Ti support. Our findings suggest that TiO2 - nanotube/Ti support is a promising substrate for the preparation of metallic nano-clusters on a support containing acidic active sites. Copyright (C) 2009 John Wiley & Sons, Ltd.