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摘要 拓扑绝缘体是一种新的量子物质态。它和传统意义上的金属、绝缘体不同。其体材料是绝缘体,有能隙；表面则是无能隙的金属态，且电子自旋方向与动量方向之间保持手性关系。这种表面态受时间反演对称保护，不易被体系中的杂质和缺陷影响。这样，电子在拓扑绝缘体中通过没有能量耗散。所以，拓扑绝缘体因其独特的表面性质掀起了研究的新热潮，无论是在材料科学领域还是凝聚态学科领域。而且，拓扑绝缘体在基础研究和量子计算、自旋电子器件等领域也都具有巨大科学价值。 微电子技术的发展和器件集成度的提高使得电子器件越来越薄、越来越小。然而，对于拓扑绝缘体薄膜，当其厚度小于一定程度之后上下表面态量子隧穿会严重影响表面的电子输运性能。如何在超薄拓扑绝缘体薄膜中保存表面态的良好性质是本文探讨的主要问题。本论文包括三部分，第一部分介绍了拓扑绝缘体的基本情况和拓扑绝缘体Bi2Se3的基本性质；在第二部分中，我们对理论基础和研究的具体工具进行说明，简要介绍了密度泛函理论，同时介绍了Abinit 软件的操作和使用方法；第三部分是第三章和第四章，着重阐述了厚度和单侧修饰对 Bi2Se3电子结构的影响，发现单侧修饰由于破坏了薄膜的对称性，有效抑制了上下表面态的量子隧穿，保护了表面态的良好性质。 最后，我们对以上结论进行了总结并对该材料将来的应用进行了展望。42041
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毕业论文关键词 拓扑绝缘体 密度泛函 超薄Bi2Se3薄膜 隧穿能隙 界面效应
Title Effects of interface on the electronic properties of ultrathin films of Bi2Se3
Abstract Topological insulator is a new quantum state. It is different from the conventional metal and insulator. The bulk of such material is an insulator with a finite excitation gap, while the surface is metallic and a chiral relation is kept between spin orientation and momentum. The surface state is protected by time reversal symmetry, which is not easily affected by the impurities and defects in the system. In this way, electrons transporting in topological insulators are dissipationless. Due to the unique surface properties of topological insulators, it has been a new research interest in the fields of materials science and condensed matter. It is also of great scientific value in the fields of fundamental research, quantum computation and spintronic devices. The electronic device units become even much thinner and smaller with the progress in microelectronic technology. However, for topological insulator films, when their thickness is small, the quantum tunneling effect will greatly degrade the metallic surface transport property. It is the focus of this thesis how preserves the great surface state properties in ultrathin topological insulator films. This thesis is consisted of three parts. In the first part, the background of topological insulator and the basic properties of Bi2Se3 are addressed; in the second part, we illustrate the theoretical foundation and the specific tools we used in our research. We also introduce density functional theory, the operation and use of Abinit software; the third part covers the third and the fourth chapters, which focuses on the influence of thickness and unilateral modification on the electronic structure of Bi2Se3. We found the single surface modification breaks the inversion symmetry of freestanding films, effectively suppresses quantum tunneling effect, and protects the excellent surface properties. Finally, we summarize the conclusions and make a prospect for the future application of this material. Keywords Topological insulator Density functional theory Ultrathin Bi2Se3 film Tunneling energy gap Interface effect
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