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Fabrication and characterization of in-situ grown epitaxial Ba1-xSrxTiO3 composition spreads K. S. Chang, M. Aronova, O. Famodu, J. Hattrick-Simpers, S. E. Lofland and I. Takeuchi Department of Materials Science and Engineering, and Center for Superconductivity Research, Department of Physics University of Maryland, College Park, MD 20742 C. J. Lu and L. A. Bendersky National Institute of Standards and Technology Gaithersburg, MD 20899 H. Chang Lawrence Berkeley National Laboratory Berkeley, CA 94720

ABSTRACT We have used our combinatorial pulsed laser deposition system to in-situ fabricate epitaxial Ba1-xSrxTiO3 thin film composition spreads on (100) LaAlO3 substrates. Multimode quantitative microwave microscopy was used to perform dielectric characterization of the spreads at multiple microwave frequencies simultaneously. Systematic variation in dielectric properties as a function of composition is studied. The multi-mode measurements allow frequency dispersion studies. We observe strong composition-dependent dielectric dispersion in Ba1–xSrxTiO3.

INTRODUCTION We report here on fabrication and characterization of in-situ grown epitaxial Ba1-xSrxTiO3 (BST) continuous composition spreads. Previous combinatorial libraries and composition spreads of BST systems were fabricated using the amorphous precursor technique [1,2]. While the precursor technique has been proven to produce high quality epitaxial films [3], films made this way often contain small pockets of off-stoichiometric and/or polycrystalline regions, which had formed as a result of incomplete precursor diffusion. For the present study, we have fabricated BST spreads with a combinatorial pulsed laser deposition (PLD) technique, which allows in-situ deposition of compositionally varying samples onto heated substrates. Microwave microscopes are ideal tools for rapid characterization and mapping of combinatorial libraries and composition spreads [1,2]. They have been used to screen the combinatorial libraries of BST and related materials systems made using the precursor technique. These studies have been fruitful in identifying novel compositions with improved dielectric properties. In the present study, we have mapped the dielectric constant of the spread as a function of frequency. We observe a systematic dispersion effect, which depends strongly on the composition. We attribute this to high-frequency relaxation, which arises from coupling of the microwave field to the phonon soft mode.

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EXPERIMENTAL For fabricating the spread, we have used our newly developed combinatorial PLD system. It is equipped with a flexible two-dimensional automated overlapping shutter system and a rotatable heater, and the entire system is contained in an eight-inch flange. Its modular design allows it to be portable [4]. Figure 1 shows the photograph of the flange.

Figure 1. Photograph of the combinatorial pulsed laser deposition flange. The shutters and the heater plates are replaceable, and different sets are used for different materials to minimize cross contaminati