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Atomic Layer Deposition of Tin Titanate - Achieving Ferroelectricity and Beyond

机译:钛酸锡的原子层沉积-实现铁电及其他

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摘要

Ferroelectric perovskites are a type of ternary oxide with ABO3 stoichiometry that possess hysteresis polarization loop under externally applied electric field. They are widely used in actuators, sensors, memory devices, etc. Some most commonly used perovskites, such as PbTiO3, are lead based materials that impose threats to environment wellness and human health. Theoreticians have proposed the replacement of Pb by its isoelectronic brother Sn, thanks to its environmental benignity, abundance and greater calculated polarization effect. Although the synthesis of polar SnTiO3 has been attempted many times -- both in bulk and as thin films, there was no success to date. In this thesis, we report the first case of atomic layer deposition (ALD) of SnTiOx, and present our original findings in process tuning, growth behavior, structural evolution, and material properties of the as-deposited and post-deposition treated samples. The ALD conditions were firstly optimized for binary oxide processes; after obtaining a wide overlapping window, co-depositions with alternating precursor sequences were carried out to grow ternary SnTiOx. To study the metastable SnOx, annealing in H2 reducing ambient was applied and the resulting samples were characterized using XPS, X-ray absorption spectroscopy, XRD and high resolution/scanning TEM. It was found that most Sn(II) was formed at annealing temperatures of 450-550C, whereas higher temperatures lead to more metallic Sn and eventually a de-wetting process. To investigate the growth behavior of SnTiOx and achieve correct stoichiometry, a set of sample were deposited with various ALD cycle ratios resulting Sn atomic % ranging from 0 to 100% in the films. Close examination and analysis of the growth rates and compositional change across these films revealed a reduced density of atoms deposited on the other oxide's surface compared to that on its own, which leads to lower growth rates at higher Sn atomic %. Possible reasons were discussed after probing the films with XPS, XRD and XRR. Lastly, those SnTiOx films with Sn:Ti atomic ratio of 1:1 were annealed in different ambient to form better crystalized structure, and then tested using piezoelectric force microscope. The sample annealed in O2 at 350C showed a hysteresis loop in amplitude, indicating possible ferroelectricity.
机译:铁电钙钛矿是一种具有ABO3化学计量比的三元氧化物,在外加电场下具有磁滞极化回路。它们被广泛用于致动器,传感器,存储设备等。一些最常用的钙钛矿,例如PbTiO3是基于铅的材料,会对环境健康和人类健康构成威胁。由于其环境良性,丰度和更大的计算极化效应,理论家提出用等电子兄弟Sn代替Pb。尽管已经尝试了多次合成极性SnTiO3的方法(无论是本体还是薄膜),但迄今为止都没有成功。在本文中,我们报告了SnTiOx原子层沉积(ALD)的第一种情况,并介绍了我们在沉积和沉积后处理的样品的工艺调整,生长行为,结构演变以及材料性能方面的原始发现。 ALD条件首先针对二元氧化物工艺进行了优化。在获得宽的重叠窗口之后,进行具有交替的前驱体序列的共沉积以生长三元SnTiOx。为了研究亚稳态的SnOx,在还原氢气的环境中进行退火,并使用XPS,X射线吸收光谱,XRD和高分辨率/扫描TEM对所得样品进行表征。发现大多数Sn(II)是在450-550℃的退火温度下形成的,而更高的温度导致更多的金属Sn并最终导致去湿过程。为了研究SnTiOx的生长行为并实现正确的化学计量,以各种ALD循环比沉积了一组样品,结果薄膜中的Sn原子%在0%到100%之间。仔细检查和分析这些薄膜的生长速率和组成变化,发现与其他氧化物相比,沉积在另一氧化物表面的原子密度降低,这导致在较高Sn原子%的情况下生长速率降低。在用XPS,XRD和XRR探测胶片后讨论了可能的原因。最后,将Sn:Ti原子比为1:1的SnTiOx薄膜在不同的环境中退火以形成更好的结晶结构,然后使用压电力显微镜进行测试。在350℃下在O2中退火的样品的振幅出现磁滞回线,表明可能存在铁电。

著录项

  • 作者

    Chang, Siliang.;

  • 作者单位

    University of Illinois at Chicago.;

  • 授予单位 University of Illinois at Chicago.;
  • 学科 Chemical engineering.;Materials science.
  • 学位 Ph.D.
  • 年度 2018
  • 页码 131 p.
  • 总页数 131
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 遥感技术;
  • 关键词

  • 入库时间 2022-08-17 11:53:11

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