Combinatorial approach to exploration of a novel fluid oxide flux stable in vacuum for material processing
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0894-LL01-05.1
Combinatorial approach to exploration of a novel fluid oxide flux stable in vacuum for material processing Y. Matsumoto1,2, H. Koinuma2, 3, 4 , Y. Tsuruta1, 2 , and R. Takahashi1, 2 1
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
2
CREST-Japan Science and Technology Corporation, 4-1-8 Honcho, Kawaguchi, Saitama 3320012, Japan
3
Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8581, Japan
4
National Institute of Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0044, Japan
ABSTRACT We explored a new fluid flux stabilized even in the vacuum condition at high temperature by combinatorial pulsed laser deposition (PLD) approach. A small amount of CuO doped in BiOx was found to effectively stabilize BiOx even in 6 Torr O2 at 800oC. The application of this novel Bi-Cu-O flux to the vacuum process lead to the successful fabrication of a single crystal Bi4Ti3O12 film and the establishment of a more reliable process for preparation of an atomically flat LaAlO3(001) substrate.
INTRODUCTION A flux, which is often used in bulk process is an admixture characterized by its fluid behavior, thereby to promote crystal growth by lowering a growth temperature and suppressing a formation of impurity phases [1]. If the flux is stable even in the vacuum condition at high temperature, we expect the same benefit from the application of flux to vacuum process. In fact, we have reported so far that Ba-Cu-O flux, which is well known as a good flux for the single crystal of high-Tc superconducting materials can exist even in 1 Torr O2 at 800oC, resulting in the successful vapor phase epitaxy of NdBa2Cu3O7-d films of which crystal quality is almost equivalent to that of the bulk single crystal [2,3]. Thus, the flux-assisted vapor phase epitaxy, as is called flux-mediated epitaxy [4] is getting more and more attractive and important concept for the coming oxide electronics. However, in order to perform flux-mediated epitaxy and the related vacuum processes, we must overcome the problem that most existing liquid fluxes are unstable in the vacuum condition at high temperature due to their high evaporative
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nature. For example, BiOx is a flux widely used for many kinds of oxide crystal growth, but cannot exist by itself in such a vacuum process. In this paper, we report on combinatorial discovery of a novel composition of BiOx-based flux stable in vacuum at high temperature and its successful applications to the vacuum process: the flux-mediated epitaxy for a single crystal Bi4Ti3O12 (BIT) film and the surface reforming for an atomically flat LaAlO3(001) substrate.
EXPERIMENTAL DETAILS In order to explore a BiOx-based flux stabilized in vacuum at a high temperature, we tried to put some impurity elements both of TiOx and MOx, where candidates of MOx are VOx, WOx, CuOx, MoOx, BiPOx and BaO. We fabricated ternary composition spreads of the flux composed of M-Bi-Ti-Ox by the use of a com
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