TEM Investigation of Epitaxial Assembly in Aggregates of BaTiO 3 and CaTiO 3 Nanocrystalline Particles Synthesized under
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TEM Investigation of Epitaxial Assembly in Aggregates of BaTiO3 and CaTiO3 Nanocrystalline Particles Synthesized under Hydrothermal Conditions Naoki Iwaji, Hiromichi Takebe, and Makoto Kuwabara Department of Applied Science for Electronics and Materials, Kyushu University, 6-1 Kasuga Koen, Kasuga, 816-8580, Japan ABSTRACT We investigated epitaxial assembly in aggregates of BaTiO3 and CaTiO3 nanocrystals, which were synthesized under a hydrothermal condition at 150˚C using distilled water-ethanol solvent, by transmission electron microscopy analysis. The volume ratio of distilled water-ethanol used as the solvent gives a significant influence on the crystal growth of the nanocrystals. The obtained results indicate that epitaxial assembly is surely involved in the crystal growth of BaTiO3 and CaTiO3 nanocrystals under the present thermal condition. INTRODUCTION For years, many scientists around the world have made research about unique property of functional nanocrystals (or nanoparticles) originating from the dimensionality on a nanometer length scale. This trend is no exception even for electronic materials used in various electronic devices. Because of recent demands relating high performance and miniaturization of electronic devices, lots of work has been done for establishment of methods to fabricate nanoparticles devices with high performance unique electronic, magnetic and optical functions. One of effective methods for such purposes may be the bottom-up method by use of controlled crystal growth from atom or molecular revels in liquid phase systems. However, the building-up of nanocrystals into devices of large sizes for practical use without degradation of their high performance functions is essentially difficult, and this is a crucial problem to be solved in relation to the bottom-up method. If nano-sized single crystalline particles can be assembled into an aggregate with crystallographically single-crystalline nature by aligning the individual particles to have the same crystallographic axes, this method to build up nanocrystalline particles as building blocks can be a very promising method for fabrication of high performance nanocrystalline functional devices; epitaxial assembly of nanocrystalline particles may play the central role in the method. Epitaxial assembly (in other words; epitaxial contact or oriented attachment) of nanocrystals into highly oriented aggregates with crystallographically single-crystalline nature is a very interesting phenomenon from both theoretical and practical points of view of nanocrystal science, which has been observed in aggregates of many kinds of nanocrystals. Typical examples of epitaxial assembly of nanoparticles have been reported for colloidal suspensions of TiO2 [1, 2], ZnO [3], and CdTe [4], treated under specific conditions. Although there have been some studies on epitaxial assembly of nanoparticles as an important mode of crystal growth [5, 6], it’s mechanism still remains insufficiently understood. We have found definite evidence of epitaxial ass
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