Influence of TiO2-Coating Layer on Nanoporous Alumina Membranes by ALD Technique

Abstract

Geometrical, chemical, optical and ionic transport changes associated with ALD of TiO 2 -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 TiO 2 -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 TiO 2 -coating of NPAMs. Considering the common application of NPAMs in solute/ion diffusion processes, the effect of the TiO 2 -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.

Influence of ALD Coating Layers on the Optical Properties of Nanoporous Alumina-Based Structures

“…Figure 1d shows a scheme of a single layer nanoporous alumina-based structure, and to deposit a coating layer thickness of around 5 nm, the number of coating cycles was adjusted according to the growth rates of the respective oxides. For TiO 2 deposition, performed at a substrate temperature of 200 • C, a growth rate of 0.05 nm/cycle was obtained, which was the reliability of this value for the NPAS + TiO 2 sample already confirmed by the TEM and XPS depth-profile analysis [30,31]. Meanwhile, SiO 2 deposition, carried out at 150 • C, yielded a deposition rate of 0.06 nm/cycle, as previously reported [18,29].…”

“…It is worth clarifying that the AZO layer consisted of a mixture of Zn and Al oxides obtained by performing 20 deposition cycles of ZnO, followed by one cycle of Al2O3, which corresponded to most of the external surface; through this approach, a doping of around 3% of Al in the ZnO layer was obtained [33,34]. According to previous results by SEM image analysis [30], a single layer coverage caused a reduction in pore size (dp) and porosity (θ) of around 20% and 30%, respectively (dp = (25 ± 2) nm, θ= 6%), while in the case of the double layer, ALD coating of the NPAS was performed in a Savannah 100 thermal ALD reactor from Cambridge Nanotech (Waltham, MA, USA), working in exposure mode. High purity argon or nitrogen was employed as the carrier gas, with a typical flow of 50 sccm.…”

Growth without Postannealing of Monoclinic VO2 Thin Film by Atomic Layer Deposition Using VCl4 as Precursor

“…Among them, ALD is an excellent technique which has drawn much attention due to its many advantages, including preparation of the highly conformal thin films with almost 100% step coverage, accurate control of film thickness at the atomic scale, low growth temperature, and wide-area uniformity. These features make ALD a powerful technique for the fabrication of emerging nanostructures and nanodevices [51][52][53].…”

Flexible 3D Electrodes of Free-Standing TiN Nanotube Arrays Grown by Atomic Layer Deposition with a Ti Interlayer as an Adhesion Promoter

“…In addition, ALD can form a homogeneous thin coating layer of different materials with surface modification [26]. ALD allows for excellent deposition conformality and step coverage with high aspect-ratio, even in nanoporous and 3-dimensional structures [27,28].…”