In-Situ X-Ray Observations of Sn Electrodeposition into Anodized Alumina
Authors: Linpe Weronica , Harlow Gary Steven , Evertsson Jonas , Hejral Uta , Lenrick Filip , Seifert Soenke , Vinogradov Nikolay , Lundgren Edvin 
Published: February 2020

Aluminum is used widely for various products and application because of its characteristics of high strength, low density and good corrosion resistance. When aluminum is exposed to air a native oxide forms on its surface and protects it from corrosion[1,2]. The native oxide can by an electrochemical method called anodization be grown thicker to give a better corrosion protection of the aluminum[3]. By using acidic electrolytes for the anodization the grown oxide will become porous, these pores can become ordered under certain anodization conditions[4]. The grown Nano-Porous Anodic Aluminum Oxide (NP-AAO) can be used as a template for growing nano wires and can be colored by deposition of metals into the pores.
We have followed in-situ the electrochemical deposition of Sn into the NP-AAO by Grazing Transmission Small Angle X-Ray Scattering (GTSAXS), X-Ray Fluorescence (XRF) and X-Ray Absorption Near Edge Structure (XANES). A two-step anodization method was used to create the ordered NP-AAO, this is achieved by anodizing the sample in acidic electrolytes in two anodizing steps with a chemical etch between the steps. The second anodization step was followed in-situ with GTSAXS[5]. To achieve a better deposition into the pores of the oxide, either a barrier layer thinning or a pore widening step was used after the second anodization. These methods will decrease the barrier layer at the bottom of the pores by a controlled down stepping of the anodization potential and make the pores wider trough a chemical etch. Both methods were followed continuously by GTSAXS.
The electrochemical deposition of Sn was achieved using an alternating voltage and an electrolyte containing tin ions. We followed the deposition continuously with GTSAXS, while XRF and XANES was measured at intervals during the deposition. Our GTSAXS measurements shows an increase in intensity during deposition, indicating deposition into the pores of the aluminum oxide. From our XRF measurements an increase of deposited Sn could be detected as the XRF signal at the sample increased over time. We used XANES for determining the chemical state of the deposited Sn.
Ex-situ FIB-SEM measurements shows the pores filled with Sn, confirming the in-situ measurements. The sample also had a change in color confirming the Sn presence inside the NP-AAO.

References

L.P.H. Jeurgens, W.G. Sloof, F.D. Tichelaar, C.G. Borsboom, E.J. Mittemeijer, Determination of thickness and composition of aluminium-oxide overlayers on aluminium substrates, Appl. Surf. Sci. 144, 11 (1999)

J. Evertsson et al, The thickness of native oxides on aluminum alloys and single crystals, Appl.Surf. Sci. 349, 826 (2015)

F. Bertram et al, In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy, J. Appl. Phys. 116, 034902, (2014)

W. Lee. and S.-J. Park, Porous Anodic Aluminum Oxide: Anodization and Templated Synthesis of Functional Nanostructures, Chem. Rev. 114, 7487 (2014)

Nikolay A. Vinogradov, Gary S. Harlow, Francesco Carlà, Jonas Evertsson, Lisa Rullik, Weronica Linpé, Roberto Felici, and Edvin Lundgren, Observation of Pore Growth and Self-Organization in Anodic Alumina by Time-Resolved X-ray Scattering, ACS Applied Nano Materials, Article ASAP