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

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.

Surface Modification of Nanoporous Anodic Alumina during Self-Catalytic Atomic Layer Deposition of Silicon Dioxide from (3-Aminopropyl)Triethoxysilane

“…A constant flow of 50 sccm of high purity argon gas was employed as both, purge and carrier gas. Additional details of the ALD deposition sequence can be found elsewhere [ 7 , 12 ]. A total of 80 deposition cycles were performed, being the ALD process stopped after an additional APTES pulse (sample Ox+SiO 2 /APTES) or after an APTES/H 2 O/O 3 pulse sequence (sample Ox+SiO 2 /APTES/O 3 ).…”

“…Depending on the material of choice for the ALD deposition, different features of nanoporous membranes can be tuned or improved. In fact, nanoporous alumina structures (NPASs) or membranes (NPAMs) obtained by electrochemical anodization of aluminium (two step anodization method [ 9 , 10 ]) consisting in a parallel array of cylindrical pores with narrow pore radius distribution and without tortuosity, whose geometrical parameters (pore size, interpore distance and pore length) can be selected depending on the electrochemical anodization conditions have demonstrated to be adequate supports for ALD deposition of one or two layers of different ceramic oxides, thus enabling to modify their pore-size/porosity and physicochemical characteristics (surface chemistry, selectivity, electrical and diffusive properties) as well as optical characteristics (refraction index, light transmission,…) [ 7 , 8 , 11 , 12 ]. Lately, NPASs have been considered as very good candidates to develop chemical/biological sensors due to their biocompatibility (which can be improved by a given coating layer) and high aspect ratio, which favours the enhancement of optical signals by pore-walls modification with specific molecules [ 13 , 14 ].…”

Optical and Electrochemical Characterization of Nanoporous Alumina Structures: Pore Size, Porosity, and Structure Effect

“…Particularly, surface coverage of NPASs with an Al 2 O 3 layer by the ALD method for pore size/porosity reduction was performed, and these results indicate only a small effect on diffusive ionic transport as determined by concentration potential measurements, but surface coverage with layers of other ceramic oxides (SiO 2 , TiO 2 , Fe 2 O 3 , or ZnO) seems to affect electrochemical transport parameters [26,[28][29][30]. Moreover, NPASs coverage with monolayers and bilayers of different ceramic oxides seems to modify characteristic optical parameters such as the refraction index or the extinction coefficient of the original sample according to spectroscopic ellipsometry (SE) results [29,30]. In this context, changes in different optical characteristics of NPASs associated to differences in their geometrical parameters (pore size, porosity, and thickness) have also been reported [15,[31][32][33].…”

“…Another significant characteristic of NPASs is the easy modification of geometrical and/or functional parameters by surface coverage/modification using different techniques such as dip coating, chemical vapor deposition, or atomic layer deposition (ALD), which can be selected depending on layer characteristics or specific NPAS application [23][24][25][26][27][28]. Particularly, surface coverage of NPASs with an Al 2 O 3 layer by the ALD method for pore size/porosity reduction was performed, and these results indicate only a small effect on diffusive ionic transport as determined by concentration potential measurements, but surface coverage with layers of other ceramic oxides (SiO 2 , TiO 2 , Fe 2 O 3 , or ZnO) seems to affect electrochemical transport parameters [26,[28][29][30]. Moreover, NPASs coverage with monolayers and bilayers of different ceramic oxides seems to modify characteristic optical parameters such as the refraction index or the extinction coefficient of the original sample according to spectroscopic ellipsometry (SE) results [29,30].…”

Cylindrical Magnetic Nanowires Applications

“…3a) and shows that controlled diameter modulations can be achieved along the channel. This fact has been exploited to tune the optical properties of the template [63], [73] and is envisioned to be used in coatings [74] and steam generation [75], for example. For more information on applications of alumina templates, the reader is referred to the excellent reviews by Lee [48] and Sulka [47].…”