Combinatorial optimization of atomically controlled growth for oxide films by the carrousel type laser molecular beam ep
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Combinatorial optimization of atomically controlled growth for oxide films by the carrousel type laser molecular beam epitaxy R. Takahashi, Y. Matsumoto, H. Koinuma Materials and Structures Laboratory and Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuda, Midori-ku, Yokohama 226-8503, Japan M. Lippmaa, M. Kawasaki Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuda, Midori-ku, Yokohama 226-8503, Japan Email : [email protected] Keyword : Combinatorial laser MBE, RHEED, perovskite, crystal habit Abstract A new combinatorial pulsed laser deposition system has been developed for rapid optimization of epitaxial growth process by using a carrousel type masking plate. Under in-situ monitoring of growing surface with reflection high energy electron diffraction, eight films with different compositions or preparation parameters can be fabricated on a single substrate. By using this system, we have succeeded in the one lot optimization of YBa2Cu3O7-d(YBCO), PrGaO3, SrO and BaO film growths on the B-site (TiO2) terminated SrTiO3(001) substrates. Key results from these experiments include the high sensitivity of YBCO film crystallinity to the laser focusing as well as of growth behavior of epitaxial SrO and BaO films to the crystal habit with the underlying atomic layers. 1. Introduction Combinatorial technology attracts much interest not only for high-throughput screening, but also for quickly optimizing process parameters for material research [1-3]. We have already developed several types of combinatorial laser molecular beam epitaxy (CLMBE) systems and verified that they were useful for atomically controlled epitaxy of ceramics thin films [4-7]. In order to quickly optimize the film growth process by looking at the surface with reflection high energy electron diffraction (RHEED), we designed and assembled the carrousel deposition system. This paper demonstrates the capability of this system in the quick optimization of YBa2Cu3O7-d (YBCO), PrGaO3, SrO and BaO film growths on SrTiO3. Using the B-site(TiO2) terminated SrTiO3(001) substrate enables us to judge the optimization by monitoring the RHEED pattern and oscillation [8]. The system application is also verified in the basic analysis of thin film growth process: crystal habit in the molecular layer epitaxy of the rock-salt SrO and BaO films. S1.4.1
Fig. 1 The schematic diagram of the carrousel deposition and in-situ RHEED monitoring system 2. Experimental Film deposition technique used in this study was a combinatorial laser molecular beam epitaxy (laser MBE). KrF excimer laser (248nm) pulses were focused on a rotating ceramics target of YBCO, PrGaO3, SrO2 or BaO2 (99.9% purity). The SrTiO3 (001) substrates were treated with a buffered NH4F-HF, and annealed at 1200 K in 10-5 Torr of oxygen for 2 h to prepare the surface composed of 4A steps and atomically flat terraces [8]. The growth conditions are summarized in Table. 1. In the CLMBE system we reported previously, epitaxial
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