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Investigation of atomic and electronic structures of LaAIOɜ/SrₓCa1-ₓTiOɜ/SrTiOɜ interfaces using Cs-corrected STEM and EELS : 투과전자현미경을 이용한 산화물 계면의 구조 관찰

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공과대학 재료공학부
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서울대학교 대학원
Cs corrected Transmission Electron Microscopy
학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2015. 8. 김미영.
Investigation of atomic and electronic structures of
LaAlO3/SrxCa1-xTiO3/SrTiO3 interfaces
using Cs-corrected STEM and EELS

Woonbae Sohn
Department of Materials Science and Engineering
College of Engineering
Seoul National University

Two dimensional electron gas (2DEG) has got an intense interest since it was discovered in the LaAlO3/SrTiO3 interface in 2004. Many researches were carried out to reveal the origin of the 2DEG but there is not any established theory. On the other hand, in the year 2013, there is a report about electrical properties of LaAlO3/SrxCa1-xTiO3/SrTiO3. In this report, as the composition of Sr increases, the interfacial conductivity increases by 6 order of magnitude. Difference in the degree of TiO6 octahedral tilt was suggested as the origin of the difference in electrical properties of the interfaces. The research is motivated by this report.
In this work, atomic and electronic structures of the LaAlO3/CaTiO3/SrTiO3 and LaAlO3/SrTiO3 were investigated using Cs corrected TEM and EELS. Each samples showed same tendency in sheet resistance as that of the previous report. High resolution HAADF and ABF STEM images showed that CaTiO3 has considerable degree of octahedral rotation whereas we could hardly observe octahedral rotation at the SrTiO3 substrate in LaAlO3/SrTiO3 system. However, considerable amount of Ti3+ was detected in both samples. From this, we concluded that regardless of the portion of Ti3+ at the interface, TiO6 octahedral tilt angle plays a crucial role determining interfacial conductivity. To generalize this statement, we will try the same procedure in the LaAlO3/Sr0.5Ca0.5TiO3/SrTiO3 system.

Keywords : Two Dimensional Electron Gas, Cs corrected transmission electron microscope, octahedral tilt, perovskite oxide
Student Number : 2013-20605
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