Spectroscopic ellipsometry and scanning electron microscopy (SEM) experiments are employed to characterize porous aluminum oxide obtained by anodization of thin aluminum films. Rutherford backscattering spectra and x-ray diffraction experiments provide information on the composition and the structure of the samples. Results on our thin film samples with a well-defined geometry show that anodization of aluminum is reproducible and results in a porous aluminum oxide network with randomly distributed, but perfectly aligned cylindrical pores perpendicular to the substrate. The ellipsometry spectra are analyzed using an anisotropic optical model, partly based on the original work by Bruggeman. The model adequately describes the optical response of the anodized film in terms of three physically relevant parameters: the film thickness, the cylinder fraction, and the nanoporosity of the aluminum oxide matrix. Values of the first two quantities, obtained from fitting the spectra, are in perfect agreement with SEM results, when the nanoporosity of the aluminum oxide matrix is taken into account. The validity of our optical model was verified over a large range of cylinder fractions, by widening of the pores through chemical etching in phosphoric acid. While the cylinder fraction increases significantly with etch time and etchant concentration, the nanoporosity remains almost unchanged. Additionally, based on a simple model considering a linear etch rate, the concentration dependence of the etch rate was determined.
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1 October 2003
Research Article|
October 01 2003
Structural and optical characterization of porous anodic aluminum oxide
Aurelian C. Gâlcă;
Aurelian C. Gâlcă
Solid State Physics, MESA+Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
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E. Stefan Kooij;
E. Stefan Kooij
Solid State Physics, MESA+Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
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Herbert Wormeester;
Herbert Wormeester
Solid State Physics, MESA+Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
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Cora Salm;
Cora Salm
Solid State Physics, MESA+Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
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Victor Leca;
Victor Leca
Low Temperature Division, MESA+Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
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Jan H. Rector;
Jan H. Rector
Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081HV Amsterdam, The Netherlands
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Bene Poelsema
Bene Poelsema
Solid State Physics, MESA+Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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J. Appl. Phys. 94, 4296–4305 (2003)
Article history
Received:
April 28 2003
Accepted:
July 08 2003
Citation
Aurelian C. Gâlcă, E. Stefan Kooij, Herbert Wormeester, Cora Salm, Victor Leca, Jan H. Rector, Bene Poelsema; Structural and optical characterization of porous anodic aluminum oxide. J. Appl. Phys. 1 October 2003; 94 (7): 4296–4305. https://doi.org/10.1063/1.1604951
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