物理化学学报 >> 2020, Vol. 36 >> Issue (11): 1906019.doi: 10.3866/PKU.WHXB201906019

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PbTiO3/SrTiO3(010)异质界面上的周期性失配位错及电子富集

陈星, 田鹤(), 张泽   

  • 收稿日期:2019-06-04 录用日期:2019-06-28 发布日期:2019-07-05
  • 通讯作者: 田鹤 E-mail:hetian@zju.edu.cn
  • 基金资助:
    国家重点基础研究发展计划(973)(2015CB654900)

Periodic Misfit Dislocation and Electron Aggregation at (010) PbTiO3/SrTiO3 Heterointerface

Xing Chen, He Tian(), Ze Zhang   

  • Received:2019-06-04 Accepted:2019-06-28 Published:2019-07-05
  • Contact: He Tian E-mail:hetian@zju.edu.cn
  • Supported by:
    the National Key Basic Research Development Program of China (973)(2015CB654900)

摘要:

探索位错等缺陷对于铁电材料畴结构、铁电性、电导率等其他物理属性的影响对于研究铁电薄膜材料的铁电及压电机理有着至关重要的作用,关于界面位错对铁电薄膜材料物理性质产生影响的现有研究结果也还存在争议,有待深入探究。本文采用球差矫正透射电镜(STEM)以及电子能量损失谱(EELS)研究了(010)晶面PbTiO3/SrTiO3异质界面上的周期性失配位错的原子结构及电荷分布。分析结果发现在a[001]位错核区域及其附近,可能存在着电子富集的现象,该现象可能会提高位错线上的电子电导率,该结果对于探究位错对铁电异质结体系物理性质的影响具有意义。

关键词: PbTiO3, SrTiO3, 异质界面, 失配位错, 球差矫正透射电镜, 电子能量损失谱

Abstract:

It is important to determine the effects of misfit dislocations and other defects on the domain structure, ferroelectricity, conductivity, and other physical properties of ferroelectric thin films to understand their ferroelectric and piezoelectric behaviors. Much attention has been given to ferroelectric PbTiO3/SrTiO3 or PbZr0.2Ti0.8O3/SrTiO3 heterointerfaces, at which improper ferroelectricity, a spin-polarized two-dimensional electron gas, and other physical phenomena have been found. However, those heterointerfaces were all (001) planes, and there has been no experimental studies on the growth of (010) PbTiO3/SrTiO3 heterointerface due to the 6.4% misfit between two materials. In this study, we selected an atomically flat (010) PbTiO3/SrTiO3 heterointerface grown using a two-step hydrothermal method as the research subject, and this is the first experimental report on that interface. Interfacial dislocations can play a significant role in causing dramatic changes in the Curie temperature and polarization distribution near the dislocation cores, especially when the size of a ferroelectric thin film is scaled down to the nanoscale. The results of previous studies on the effects of interfacial dislocations on the physical properties of ferroelectric thin films have been contradictory. Thus, this issue needs to be explored more deeply in the future. This study used aberration corrected scanning transmission electron microscopy (STEM) to study the atomic structure of a (010) PbTiO3/SrTiO3 heterointerface and found periodic misfit dislocations with a Burgers vector of a[001]. The extra planes at the dislocation cores could relieve the misfit strain between the two materials in the [001] direction and thus allowed the growth of such an atomically sharp heterointerface. Moreover, monochromated electron energy-loss spectroscopy with an atomic scale spatial resolution and high energy resolution was used to explore the charge distribution near the periodic misfit dislocation cores. The fine structure of the Ti L edge was quantitatively analyzed by linearly fitting the experimental spectra recorded at various locations near and at the misfit dislocation cores with the Ti3+ and Ti4+ reference spectra. Therefore, the accurate valence change of Ti could be determined, which corresponded to the charge distribution. The probable existence of an aggregation of electrons was found near the a[001] dislocation cores, and the density of the electrons calculated from the valence change was 0.26 electrons per unit cell. Based on an analysis of the fine structure of the oxygen K edge, it could be argued that the electrons aggregating at the dislocation cores came from the oxygen vacancies in the interior regions of the PbTiO3. This aggregation of electrons will probably increase the electron conductivity along the dislocation line. The physics of two-dimensional charge distributions at oxide interfaces have been intensively studied, however, little attention had been given to the one-dimensional charge distribution. Therefore, the results of this study can stimulate research interest in exploring the influence of the interfacial dislocations on the physics of ferroelectric heterointerfaces.

Key words: PbTiO3, SrTiO3, Heterointerface, Misfit dislocation, Aberration corrected transmission electron microscopy, Electron energy-loss spectroscopy

MSC2000: 

  • O649