Influence of TiO2-Coating Layer on Nanoporous Alumina Membranes by ALD Technique
Department of Física Aplicada I, Facultad de Ciencias, Universidad de Málaga, E-29071 Málaga, Spain
Unidad de Nanotecnología, SCBI Centro, Universidad de Málaga, E-29071 Málaga, Spain
Servicios Centrales de Investigación, Universidad de Málaga, E-29071 Málaga, Spain
Laboratorio de Membranas Nanoporosas, Servicios Científico-Técnicos, Universidad de Oviedo, E-33006 Oviedo, Spain
Department of Física, Facultad de Ciencias, Universidad de Oviedo, E-33007 Oviedo, Spain
Author to whom correspondence should be addressed.
Coatings 2018, 8(2), 60; https://doi.org/10.3390/coatings8020060
Received: 15 December 2017 / Revised: 29 January 2018 / Accepted: 31 January 2018 / Published: 7 February 2018
(This article belongs to the Special Issue Nanostructured Functional Coatings)
Geometrical, chemical, optical and ionic transport changes associated with ALD of TiO2-coating on the porous structure of two nanoporous alumina membranes (NPAMs), which were obtained by the two-step aluminum anodization method but with different pore size and porosity, are presented. Chemical and morphological changes were determined by analyzing XPS spectra and SEM images, showing practically total coverage of the NPAMs surface and leading to a reduction in the geometrical parameters of both samples, while SAED and high resolution TEM measurements allowed us to determine the crystalline structure and thickness of the TiO2-coating, with the latter confirmed by depth-profile XPS analysis. Spectroscopic ellipsometry measurements were also carried out in order to detect changes in characteristic optical parameters (refractive index, n, and extinction coefficient, k), due to the TiO2-coating of NPAMs. Considering the common application of NPAMs in solute/ion diffusion processes, the effect of the TiO2-coverage on electrochemical parameters was analyzed by measuring the concentration potential with a typical model electrolyte (KCl solutions), leading to an increase of the electropositive character for both kinds of samples.