Atomic Layr Epitaxy and Property of Artificial Superlattice with Perovskite Type Structure

本研究采用分子束外延技术制备了钙钛矿型BaTiO_3-SrTiO_3人工超晶格，并对其晶体结构进行了分析。我们还测量了超晶格的介电性质。主要研究结果如下：1)采用原子层外延技术制备BaTiO_3-SrTiO_3超晶格，采用分子束外延技术，将组成元素逐层原子外延。开发了计算任意结构人工超晶格X射线衍射图的软件，并用于结构分析。计算结果与实验结果吻合较好，考虑了BaTiO_3和SrTiO_3在界面层上的热扩散。为了防止组成元素的热扩散，尝试在SiTiO_3衬底上低温外延BaTiO_3。结果表明，在400ﾟC的低能氧离子束照射下，可以实现薄膜的外延生长。4)测量了沉积在导电钛酸锶衬底上的人工超晶格的介电性能。即使超晶格的总厚度和化学成分相同，介电性能也会随着超晶格的结构发生显着的变化。

In the present study, we have developed a fabrication process of BaTiO_3-SrTiO_3 artificial superlattices with Perovskite type structure by molecular beam epitaxy, and analyzed the crystal structure of the superlattices. We have also measured dielectric property of the superlattices. Results of the research are summarized as follows.1) BaTiO_3-SrTiO_3 superlattices could be fabricated by atomic layr epitaxy where constituent elements were deposited atomic layr-by-layr using a molecular beam epitaxy technique.2) Crystal structure analysis method of artificial superlattice was developed. A software which calculates X-ray diffraction pattern of an artificial superlattice with arbitrary structure was developed and used for structure analysis. It was found calculation and experimental results agreed well by taking into account thermal diffusion of Ba and Sr atoms at interface layr between BaTiO_3 and SrTiO_3.3) In order to prevent the thermal diffusion of constituent elements, a low temperature epitaxy of BaTiO_3 on SiTiO_3 substrates was tried. It was found that epitaxial growth was achieved at 400ﾟC by irradiating low energy oxygen ion beam.4) Dielectric property of the artificial superlattice deposited on a conductive SrTiO_3 substrates was measured. Dielectric property was markedly changed with the structure of the superlattices even if the total thickness and chemical composition of the superlattices were identical.