Probing Barrier Oxide Layer of Porous Anodic Alumina by In Situ Electrochemical Impedance Spectroscopy

Abstract

Electrochemical impedance spectroscopy (EIS) is a unique tool for both ex situ and in situ studies of the barrier layer thickness of anodic aluminium oxide (AAO). Here EIS is applied to study porous AAO formed by anodizing of high-purity Al foils in 0.3 M sulphuric acid and 0.3 M oxalic acid electrolytes. It is shown that in the high-frequency range, in situ EIS spectra coincide with the ex situ ones. Thus, the thickness of the barrier layer at the pore bases does not change after the end of the anodic polarization. The barrier layer thickness (h) is governed by the anodizing potential (U) according to the equation h = 1.03(2) nm·V−1·U + 2.2(3) nm. Features of the current transients observed during potentiostatic anodizing are discussed. It has been proved that a local maximum of current at the initial stage of anodizing corresponds to the maximum of the aluminium electroactive surface area arising due to the rearrangement of pores.

Ion beam etching of anodic aluminium oxide barrier layer for Au nanorod-based hyperbolic metamaterials

“…Ion etching of the barrier layer of ca. 44 nm in thickness 43 was carried out using a parallel beam of Ar + ions directed at an angle of 45° to the film surface. SEM images of the bottom surface of the resulting samples are shown in Fig.…”

Simulation-Assisted Process Design and Experimental Verification of Laterally Confined Oxide Areas Generated with Continuous Electrolytic Free Jet on EN AW-7075 Aluminum Alloy

“…To evaluate the formed barrier layer thickness, the following Equation (12) was used assuming that the barrier layer has the only contribution to the oxide layer capacitance since the impact of the porous layer can be neglected [ 17 ]: …”

“…Here, is the permittivity of aluminium oxide with a value of 8.5 according to [ 17 ], is the vacuum permittivity, is the surficial area of the sample, and is the capacitance of the anodic oxide layer measured in experiments from Table 2 . The calculation results is an average value of 50.3 nm for the thickness of the barrier layer and a value of 7.25 × 10 7 S/m for the electrical conductivity of the barrier layer.…”

“…The measurement time of each EIS measurement was approximately 61 s. The results were fitted using the software ZahnerAnalysis provided by the manufacturer of the workstation. The equivalent circuit diagram shown in Figure 1 was derived from Leontiev and Napolskii [ 17 ], who also performed EIS measurements during anodizing at constant potential in an oxalic acid solution.…”

Morphological and semiconductive properties of the anodic oxide layers made on Fe3Al alloy by anodizing in tartaric-sulfuric acid mixture

“…Fe 3 Al anodizing at 10–15 V in EG-containing electrolytes results in less porous surfaces, lower pore diameters, and thinner films than those formed at 0 vol.%-EG electrolyte at the same voltage range (10–15 V) (Table 3 ). Again, this may be due to the reduced current density registered during the process, which, in turn, affected the barrier layer resistivity 33 , 34 and, to some extent, the decreased ionic migration during anodizing in EG-containing electrolytes 35 , 40 .…”