Reflection spectra and optical constants of quasicrystalline Al-Pd-Re films in the IR region
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Reflection Spectra and Optical Constants of Quasicrystalline Al–Pd–Re Films in the IR Region V. A. Yakovleva, N. N. Novikovaa, G. Matteib, A. A. Teplovc, D. C. Shaœturac, D. I. Dolgiœc, and E. D. Ol’shanskiœc a
Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow oblast, 142190 Russia b Instituto dei Sistemi Complessi ISC, CNR, C.P. 10, Monterotondo Sc. (RM), I-00016 Italy c Russian Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia e-mail: [email protected] Received April 17, 2007
Abstract—Optical properties of quasicrystalline Al–Pd–Re films have been investigated in the mid and far IR regions. Films were deposited on sapphire substrates using layer-by-layer ion-plasma sputtering with subsequent vacuum annealing. Reflection spectra have been measured in a wide IR spectral range from 50 to 7500 cm–1. The complex dielectric function of the films was determined from the experimental data by dispersion analysis of the reflection spectra. The frequency dependence of the real part of the optical conductivity was calculated. PACS numbers: 61.44.Br, 78.66.-w DOI: 10.1134/S106377450706017X
INTRODUCTION The interest in quasicrystalline films is related in many respects to the prospects of their practical application. For example, there was an attempt to use a quasicrystal as one of the layers of a multilayer coating for selective absorbers of solar radiation [1, 2]. At the same time, the physical properties of quasicrystalline films have been studied insufficiently well; in particular, this concerns the optical properties. For the Al–Pd–Re system, investigations of the optical properties have been performed on bulk samples [3, 4], but such investigations on films have been performed for the first time. The optical properties of Al–Pd–Re quasicrystalline films were investigated by the methods of mid- and farIR reflection. Films with thicknesses up to 300 nm on sapphire substrates were investigated. Samples of Al–Pd–Re films (see table) were prepared by layer-by-layer ion-plasma deposition with subsequent vacuum annealing. Deposition was performed in a vacuum system with a sputtering chamber in the form of a Penning cell; krypton was used as a
working gas. Samples were deposited on sapphire plates successively in the Al–Pd–Re combination, which was repeated three times to obtain a higher film homogeneity for the samples with a thickness of 300 nm and once for thinner samples. After deposition of a layered structure, the films were coated with a layer of aluminum oxide, which was formed by sputtering of aluminum in a krypton atmosphere with addition of oxygen. The aluminum oxide layer was deposited to prevent selective escape of elements from the film upon vacuum annealing. The concentration range for the films prepared coincided with the known range of quasicrystalline phase formation in bulk samples. Annealing was performed in vacuum in two stages: at 350°ë for 3 h and then at 700°ë for 2 h. The samples annealed were investigated by X-ray diffraction. The
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