Combinatorial Synthesis and Evaluation of Functional Inorganic Materials Using Thin-Film Techniques
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Combinatorial
Synthesis and Evaluation of Functional Inorganic Materials Using Thin-Film Techniques
Ichiro Takeuchi, Robert Bruce van Dover, and Hideomi Koinuma Abstract Novel phases of functional inorganic chemical systems can be efficiently explored using high-throughput thin-film fabrication techniques coupled with rapid characterization schemes. High-throughput investigation of thin-film materials has already led to the discovery of new dielectric and magnetic materials. In this article, we review various high-throughput thin-film synthesis/evaluation techniques and discuss examples of exciting discoveries and new applications of combinatorial techniques. Keywords: advanced dielectrics, combinatorial methods, composition spreads, concurrent x-ray diffractometer, thin films, laser molecular-beam epitaxy, scanning evanescent microwave probe, transparent magnetic materials.
Introduction The discovery of novel functional materials can be efficiently accomplished using high-throughput thin-film fabrication techniques coupled with rapid characterization schemes. Combinatorial thin-film “libraries” have been prepared using discrete, sequentially masked depositions, codeposited composition spreads, and composition-gradient molecular layer epitaxy. Measurement techniques have been adapted for quick evaluation of the libraries and composition spreads, mapping a variety of physical characteristics including optical, electrical, and magnetic properties. High-throughput investigation of thin-film materials has
MRS BULLETIN/APRIL 2002
already led to the discovery of exciting new and useful dielectric (Zr0.2Sn0.2Ti0.6O2 ; Ba 0.12–0.25 Sr0.35–0.47 Ca 0.32–0.53TiO3) and magnetic (Co-doped TiO2) materials. It has also facilitated investigations of the detailed composition dependence of properties in systems that are already known but have been incompletely studied. In this article, we review successful discoveries and applications of these combinatorial materials libraries.
Thin-Film Library Synthesis The effort to directly transfer the organic combinatorial synthesis concept to inorganic thin-film materials was started
by a group at the Lawrence Berkeley National Laboratory.1 In adopting this synthetic approach to simultaneously creating large arrays of thin-film samples, the precursor deposition method was used. This approach can truly bring out the combinatorial nature of the synthesis because it enables the production of a large number of different compositions by generating many permutations of precursors. On a substrate as small as 1 cm2, thousands of different compositions can be integrated, synthesized, and screened for desired physical properties in a single experiment. This method takes advantage of the fact that in many materials systems it is possible to grow stoichiometric compounds by means of controlled thermal diffusion of precursors. For fabricating YBa2Cu3O7, for instance, one can use amorphous layers of Y2O3, BaF2 , and CuO2 as precursors. A series of precisely positioned shadow masks, which allow spati
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