Abstract
Optical changes associated with the surface coating of different metal oxides and nanolayers by the ALD technique of a nanoporous alumina structure (NPAS) obtained by the two-step anodization method were analyzed. The NPASs were coated with: (i) a single layer (SiO2 or TiO2), and (ii) a double layer of SiO2 plus Al2O3 or aluminum doped ZnO (AZO) to estimate the effect of surface layer coverage material, geometrical parameters (pore-size/porosity), and number of layers on light transmission/reflection. Chemical surface characterization of the different NPASs was carried out by analyzing XPS spectra, which allowed us to obtain an estimation of the coating layer homogeneity. Transmittance and spectroscopic ellipsometry measurements were analyzed in order to detect changes in characteristic optical parameters such as band gap, refractive index, and extinction coefficients associated with the material and the characteristics of the single or double coating layers.
Highlights
In the last 20 years, a significant number of papers focused on exploring the application of nanoporous materials synthesized by electrochemical techniques such nanoporous anodic alumina structures (NPASs) or porous silicon structures for application in sensing devices have been published [1,2,3]
We describe the change in the optical properties associated with the surface coating of a NPAS by the atomic layer deposition (ALD) technique with different metal oxides through a single layer (SiO2 and TiO2 ) and double layer (SiO2 + Al2 O3 and SiO2 + aluminum doped ZnO (AZO)) as a way to establish differences associated with the coating-layer material and layer number, independent of pore size and the porosity of the nanoporous alumina-based structures (NPA-bSs)
NPA-bSs were determined by analyzing the x-ray photoelectron spectroscopy (XPS) spectra, taking into account the area of the corresponding signals [37]
Summary
In the last 20 years, a significant number of papers focused on exploring the application of nanoporous materials synthesized by electrochemical techniques such nanoporous anodic alumina structures (NPASs) or porous silicon structures for application in sensing devices have been published [1,2,3]. The NPASs prepared by the anodization of aluminum foil by the two-step method present had enhanced thermal and chemical resistance as well as tunable optical properties and had good biocompatibility and a large specific surface area [4,5,6,7,8]. This latter characteristic, the high specific surface area to volume ratio, is of great interest to enhance optical signals when the NPASs are incorporated into sensor devices [9]. The optical characteristics of NPASs such as light transmittance, absorbance, or reflectivity can be tools of interest for selective chemical and biochemical applications [9].
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