Nanostructured anodic porous alumina (NAPA) formation is connected with roughness of the initial aluminum [1]. Anodization spectroscopy method, a simple high-resolution way of studying films and thin-film structures, was developed for the express-control of superconducting microcircuits technology based on niobium and aluminum [2-3]. It requires non-expensive equipment and no long time to cany out the analysis.

 The aim of the work is to show that the anodization profiles method (anodization spectroscopy) may be used for monitoring of surface roughness in thin-films nanotechnologies based on NAPA.

It is well known that at anodic oxidization of the metals in the constant-current method an increment in the thickness of the oxide layer is followed by the growth of voltage on the electrolytic cell. The growth rate of the oxide layer thickness is

                                   dx/dt = λ(M/nZρF)·j                         (1)

 and the rate of the voltage change on the oxide layer is

                               dV/dt = λ(M/nZρF)· j·Е_dif                     (2)

where j is current density, M is a molecular mass of the oxide, ρ is an oxide density, n·Z is a valency of oxidation reaction, F is Faraday constant, n is the chemical efficiency, E_dif= dU/dx is the differential field strength in the oxide. Under anodization the current density is j=I/S, where I is a stabilized current through the electrolytic cell, S is an area of the anodization front. Each change of the anodization area results in the change in j and dV/dt. This fact makes possible the investigation of the relief of the anodization front and to investigate thin films layers properties (e. g. roughness) through the application of a constant direct current and the simultaneous measurement of the dV/dt versus V.

The results of the work show, that anodization spectroscopy allows to evaluate the roughness of Al films prepared in DC sputtering system under different regimes of deposition. The Al films were covered by Nb films to prevent oxidation. Special equipment for anodization and processing of the obtained anodizing profiles makes it possible to determine the roughness of the aluminum films from the width of the transition region between Nb and Al. It was shown that the roughness of Al is about 5 nm for 50 nm thickness and 150 nm for a thickness of 600 nm.

Thus, the work shows that the low-cost anodization set-up together with the possibility to explore interfacial properties on the nanometer level made anodization spectroscopy an established and attractive method in  nanotechnologies based on NAPA.

[1]     T. Lebyedyeva, S. Kryvyi P. Lytvyn, M. Skoryk, P. Shpylovyy. ‘Formation of Nanoporous Anodic Alumina by Anodization of Aluminum Films on Glass Substrates’, Nanoscale Res. Let., vol. 11, pp. 203-214, 2016. doi:10.1186/s11671-016-1412-y

[2]     T. Imamura, S. Hasuo, “Fabrication of High Quality Nb/AlOx-Al/Nb Josephson Junctions: II-Deposition of Thin Al Layers on Nb Films,” IEEE Trans. Appl. Supercond., vol. 2, pp. 84–94, 1992, doi:10.1109/77.139224

[3]     T. Lebedeva, I. Voytovytch, P. Shpylovyy, “Anodization spectroscopy express-control system for thin-film technologies,” Metal Matrix Composites and Metallic Foams, vol. 5, pp. 53 – 58,  2005.