Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with A1 2O 3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature >900 °C. ALD was used to cover the surface of AAO with either Al 2O 3 or TiO 2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al 2O 3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO 2 show a more complicated behavior. UV Raman results show that very thin TiO 2 coatings (1 nm) are not stable upon annealing to 500 °C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 °C.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry