文章信息/Info

Title:

The Atomic/Electronic Structure of Oxide Interfaces

作者:

祝國珍

 (上海交通大學材料科學與工程學院，上海 200240)

Author(s):

 Guo-zhen Zhu

School of Materials Science and Engineering, Shanghai Jiao Tong University

關鍵詞:

氧化物; 界面; 透射電子顯微術; 原子結構; 電子結構

DOI:

10.7502/j.issn.1674-3962.2016.05.04

文獻標志碼:

A

摘要:

隨著薄膜制備技術的發(fā)展和理想氧化物界面的制備，氧化物界面成為研究熱點之一，發(fā)現(xiàn)如超導性等優(yōu)異特性，進而成為電子器件的有力候選材料。相較金屬和半導體界面而言，氧化物界面的特性更具有局域性，故其闡明界面處的原子/電子結構顯得更為重要。界面并不能獨立于體相單獨存在，因此研究界面問題的關鍵是如何提取隱藏在體相中的微弱界面信息。透射電子顯微鏡作為一種局域性的表征手段，同時又具備多種技術可實現(xiàn)成像、衍射以及能譜，故成為表征氧化物界面的有力工具。通過制備截面樣品，可得到氧化物界面在不同投影面的二維結構，進而重構界面的三維原子結構。此外，通過采集包含不同比重的界面信號的一組實驗數(shù)據(jù)，可通過數(shù)學分析方法分離出界面信號。這種方法在研究界面和界面的電子結構等問題上具有一定優(yōu)勢。 

Abstract:

With the technical breakthroughs of creating oxides by novel thin film deposition techniques with well-defined interfaces, oxides have received increasing attention in the electronic and optoelectronic industry due to their unique combination of novel physical properties and the fact that oxides can form “heterostructures” for multiple devices. In order to understand the atomic/electronic structure in oxides, various characterization techniques have been involved. In the past, the characterization has been limited to broad beam techniques though X-ray absorption spectroscopy (XAS), nuclear magnetic resonance (NMR) to achieve the average physical and chemical information. With techniques such as scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), high-resolution TEM opens the path to the study of chemical composition and bonding information coupled with the atomic level images, and thus provides an ideal tool to investigate individual interfaces. Interface cannot be physically isolated from the bulk, it is difficult to correctly and effectively extract the weak signal from these interfaces presented in a solid bulk. Such extraction remains a very challenging issue even in TEM when thin foils, with thickness is less than 100 nm, area used. The visibility of these interface can be enhanced by picking up corresponding signals since the elastically scattered electrons contributing to signals from these interfaces are distributed unevenly in space and differently compared to the ones contributed by the bulk. Studying cross-sectional samples provides two-dimensional projected information of the three-dimensional interfacial structures. Accordingly, the atomic structure can be constructed though combining information from different projections. Regarding the fact that EELS signals from the defects and the bulk are distributed similarly in space, a new experimental approach, based on a “thickness” series of EEL spectra containing different bulk contributions, was proposed to effectively extract weak EELS signals from these interfaces. The development of characterization techniques such as TEM has lead to improved understanding of oxide interfaces and thus provides great opportunity to create artificial structure for their novel physical properties.