Local analysis of the two-dimensional electron systems in oxide heterostructures by nanooptical microscopy and spectroscopy

通过纳米光学显微镜和光谱法对氧化物异质结构中的二维电子系统进行局部分析

• 批准号: 315025796
• 负责人: Professor Dr. Thomas Taubner
• 金额: --
• 依托单位: PGI-7: Elektronische Materialien
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/315025796?language=en
• 关键词: Local; analysis; two; dimensional; electron

Owing to their unique physical properties, novel 2-dimensional electron gases (2DEGs) arising at interfaces between insulating oxides bear high potential for fundamental research in physics as well as for electronic applications.These 2DEGs are observed when a polar oxide (e.g. LaAlO3) is grown a non-polar transition metal oxide (e.g. SrTiO3) such that the two materials are interfacing each other with atomic precision. These 2DEGs arise because of an electronic-ionic interface reconstruction caused by the polarity discontinuity at the interface associated with an electrical dipole that grows with increasing layer thickness of the polar oxide.In this project, we aim to investigate and to understand the relation between microscopic structure and electronic properties of such interfacial 2DEGs with lateral resolution on the nanometer scale using scattering-type scanning near-field optical microscopy (s-SNOM), complemented by X-ray spectroscopy (XPEEM) and alternative scanning probe techniques.In particular, we aim to image directly inhomogeneities and local fluctuations in the 2DEG. A special focus of the project is the investigation of the local formation process of the electron gas (1) when locally traversing the critical layer thickness and (2) when locally varying the chemical interface termination. Furthermore, the project addresses (3) the local dielectric properties associated with the local defect structure of the involved materials adjacent to the interfacial 2DEG.These tasks are especially challenging since the 2DEG is located at an interface and is thus buried underneath an insulating oxide layer. s-SNOM is a unique technique that allows imaging the optical properties of such buried electron systems laterally resolved on the nanoscopic scale in a non-destructive manner. At same time, s-SNOM provides access to the local dielectric properties of the interface region through optical spectroscopy on the nanoscale.Complementing s-SNOM analysis of the buried 2DEG through the capping layer, this project addresses (4) the electron gas in cross-sectional sample geometry in order to probe the shape of the potential well at the interface.Further objectives of this project are methodical advances in the description of the optical near-field response of low-dimensional electron systems using the conducting oxide heterointerface as model system. In particular, a general model for the near-field interaction between s-SNOM probe and 2DEG has to be established (5). Moreover, a new (short wavelength) quantum cascade laser will be put into s-SNOM operation (6).The results of this project are likely to improve substantially the general understanding of interface reconstructions at oxide hetero-interfaces on the local scale. Methodical progress furthermore improves the general understanding of the optical near-field response of such systems and enables the s-SNOM technique to access other low dimensional systems in the future.

由于其独特的物理性质，在绝缘氧化物之间的界面处产生的新型二维电子气（2DEG）在物理学基础研究以及电子学应用方面具有很高的潜力。当极性氧化物（例如LaAlO 3）与非极性过渡金属氧化物（例如SrTiO 3）生长时，可以观察到这些2DEG，使得两种材料以原子精度相互接触。这些2DEG的出现是因为电子-离子界面重构引起的，该界面重构是由与电偶极子相关的界面处的极性不连续性引起的，该电偶极子随着极性氧化物的层厚度的增加而生长。我们的目标是研究和理解这种界面2DEG的微观结构和电子性质之间的关系，横向分辨率在纳米尺度上使用散射型扫描近，场光学显微镜（s-SNOM），辅以X射线光谱（XPEEM）和替代扫描探针技术。特别是，我们的目标是直接成像的不均匀性和局部波动的2DEG。该项目的一个特别重点是调查电子气的局部形成过程（1）当局部穿过临界层厚度时和（2）当局部改变化学界面终止时。此外，该项目还解决了（3）与界面2DEG相邻的相关材料的局部缺陷结构相关的局部介电特性。这些任务特别具有挑战性，因为2DEG位于界面处，因此埋在绝缘氧化物层下面。S-SNOM是一种独特的技术，它允许以非破坏性的方式在纳米尺度上横向分辨这种掩埋电子系统的光学特性。同时，s-SNOM通过纳米尺度上的光谱学提供了对界面区域的局部介电性质的访问。该项目解决了（4）交叉中的电子气，截面样品的几何形状，以探测界面处势阱的形状。本项目的进一步目标是在描述以导电氧化物异质界面为模型系统，研究了低维电子系统的光学近场响应。特别地，必须建立s-SNOM探针和2DEG之间的近场相互作用的通用模型（5）。此外，一种新的（短波长）量子级联激光器将被投入s-SNOM操作（6）。该项目的结果可能会大大提高对局部尺度上氧化物异质界面处界面重建的一般理解。方法上的进步进一步提高了对此类系统的光学近场响应的普遍理解，并使s-SNOM技术能够在未来访问其他低维系统。