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Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films |
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| Authors: | D Nuzhnyy J Petzelt S Kamba T Yamada M Tyunina A K Tagantsev J Levoska N Setter |
| Affiliation: | 1. Institute of Physics ASCR, Na Slovance 2, 18221 8, Prague, Czech Republic 2. Ceramics Laboratory, Swiss Federal Institute of Technology, EPFL, CH-1015, Lausanne, Switzerland 3. Microelectronics and Materials Physics Laboratories, and EMPART Research Group of Infotech Oulu, University of Oulu, PL 4500, Oulun Yliopisto, 900014, Oulu, Finland |
| Abstract: | Several SrTiO3 (STO) thin films without electrodes processed by pulsed laser deposition, of thicknesses down to 40 nm, were studied using infrared transmission and reflection spectroscopy. The complex dielectric responses of polar phonon modes, particularly ferroelectric soft mode, in the films were determined quantitatively. The compressed epitaxial STO films on (100) La0.18Sr0.82Al0.59Ta0.41O3 substrates (strain 0.9%) show strongly stiffened phonon responses, whereas the soft mode in polycrystalline film on (0001) sapphire substrate shows a strong broadening due to grain boundaries and/or other inhomogeneities and defects. The stiffened soft mode is responsible for a much lower static permittivity in the plane of the compressed film than in the bulk samples. |
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