钙钛矿金属氧化物异质结的第一性原理研究
发布时间：2019-07-03 10:53
【摘要】：随着科技的进步,计算机性能得到了飞速的提高,人们对物理理论的认识也更加的深入,利用计算机模拟解释物理现象以及设计功能材料已经成为不可或缺的科研手段。由于密度泛函理论在精度以及对经验参数的依赖性上具有独特的优势,使得它在众多第一性原理方法中脱颖而出。钙钛矿氧化物异质结由于其界面以及表面丰富的物理性质而吸引众多实验和理论工作者的眼光,近十年来成为物理化学界争相研究的热点。本文我们主要通过第一性原理计算,对不同种类的钙钛矿氧化物异质结在理论上进行设计和研究,涉及的内容包括对异质结光催化能力的预测,对界面二维自由电子气的调控,和对异质结拓扑性质的发现。对钙钛矿氧化物异质结在物理、化学以及电子器件方面的应用作出了理论上的预测和机理上的阐述。第一章中我们对理论计算方法细节做一个概括性的介绍。有：基于波函数的Hartree-Fock方法；基于电子密度的密度泛函理论。对它们的理论背景和发展做了详细的介绍。随后,我们对密度泛函理论中最重要最核心的交换关联泛函作了介绍,最后简单介绍了两个常用的计算软件包。第二章中我们对近十年来最热门的LaAlO3/SrTiO3(001)(LAO/STO(001))界面作了背景介绍,包括最受关注的界面二维自由电子气的产生,临界层数问题以及三种不同的机制(极化灾难模型、氧缺陷模型和离子交换模型)。随后我们对界面其他奇异的物理现象作了简单的介绍,如界面的铁磁性、超导性以及铁磁超导共存现象。第三章中,我们通过计算,提出了新的过渡-金属氧化物-异质结模型,设计出一种新型的用于光催化的材料。我们设计了一种既包含n型又包含p型界面的‘三明治”结构STO/LAO/STO(001)异质结。由于LAO(001)内部存在的本征电场随层数而增加,我们可以通过改变LAO的厚度来调节两边STO的能带位置。通过这种方法,体系的带隙有了明显变小,从而大大提高了光吸收效率,通过第一性原理计算的结果看到,当LAO厚度到达一定层数后,光吸收范围可移动至可见光甚至红外光。同时,LAO内部的电场将光激发的电子空穴对分离并向相反方向移动,有效地阻止了电子空穴对的复合,使得两边的STO分别成为电子掺杂和空穴掺杂的表面,在空间上分离了水的氧化还原反应。第四章中我们研究了应力是如何通过改变晶格结构来调控界面的二维自由电子气。根据我们的计算结果,我们认为应力对于n型LAO/STO界面体系的二维自由电子气具有重要的调控作用,通过应力引起的STO部分的铁电性与LAO本征的电场的相互作用,调节STO的铁电方向来“打开”和“关闭”界面二维自由电子气。在压缩应力情况下,我们提出的三种模型‘'para"、"up"、"down",其中“up”类型是“打开”二维自由电子气的按钮,‘'down"则是”关闭”按钮,而对于"para"型,压缩应力仍然提高了二维自由电子气出现的临界层数,拉伸应力则通过减小界面处载流子浓度以及降低其迁移率来限制二维自由电子气的出现。第五章中我们通过设计由较重的过渡金属组成的类似石墨烯的蜂窝状结构(honeycomb)来实现陈绝缘态。对称性破缺导致拓扑性的被破坏,使得寻找一种具体的此类陈绝缘体成为难点,基于之前3d系列金属氧化物的研究,我们通过调节自旋轨道耦合(SOC)以及其它相互作用,设计出两种宽带隙的陈绝缘体,带隙高达132meV,其陈数分别是C=-1及C=2。通过这个研究我们发现,SOC与其它作用的相互平衡将导致更宽的带隙,而更强的SOC会引起更大的霍尔电导。而通过结构优化而引起的对称性降低也会破坏量子反常霍尔效应的形成,在这两个具有鲁棒性的陈数绝缘体中,放开所有自由度优化过后,结构依然保持着较高的对称性。近年来发展的氧化物薄膜生长技术也给我们提供了这种绝缘体实验上的可能性。第六章中我们对本文的工作做了简单的总结和对未来的展望。
[Abstract]:With the progress of science and technology, the performance of the computer is greatly improved, and people's understanding of the physics theory is more in-depth, and the computer simulation to explain the physical phenomena and the design of the functional materials has become an indispensable scientific research means. The density functional theory has a unique advantage in the precision and dependence on the empirical parameters, making it stand out in many of the first principle methods. Perovskite-oxide heterojunction has attracted many experimental and theoretical workers due to its interface and its surface-rich physical properties. Based on the first principle, we design and study the different kinds of perovskite-oxide heterostructures, including the prediction of the photocatalytic ability of the heterojunction, the control of the two-dimensional free electron gas of the interface, and the discovery of the topological properties of the heterojunction. The application of the perovskite-oxide heterojunction in the fields of physics, chemistry and electronics has been theoretically predicted and discussed. In that first chap, we introduce a general introduction to the detail of the theoretical calculation method. There are: Hartree-Fock method based on wave function; density functional theory based on electron density. The background and development of their theories are described in detail. Then, we introduce the most important and most important exchange-related general function in the density functional theory, and then briefly introduce two commonly used calculation software packages. In the second chapter, we introduce the most popular LaAlO3/ SrTiO3 (001) (LAO/ STO (001) interface in the last ten years, including the generation of two-dimensional free electron gas, the critical number of layers and three different mechanisms (polarization disaster model, oxygen defect model and ion exchange model). Then we make a brief introduction to the other strange physical phenomena of the interface, such as the ferromagnetism, the superconductivity and the ferrosuperconducting coexistent phenomenon of the interface. In the third chapter, a new transition-metal-oxide-heterojunction model is proposed, and a new kind of material for photocatalysis is designed. In this paper, we design a structured STO/ LAO/ STO (001) heterojunction with both n-type and p-type interfaces. Since the intrinsic electric field in the interior of the LAO (001) increases with the number of layers, we can adjust the energy band position of the STOs on both sides by changing the thickness of the LAO. By this method, the band gap of the system can be changed to the visible light or even the infrared light by changing the thickness of the LAO. At the same time, the electric field inside the LAO can move to the visible light or even the infrared light when the thickness of the LAO reaches a certain number of layers. At the same time, the electric field inside the LAO is separated and moved in the opposite direction, so that the two-dimensional free electron gas of the interface can be controlled by changing the lattice structure, and the stress is considered to be n-type LAO/ STO according to our calculation result. the compressive stress still increases the critical number of layers present in the two-dimensional free electron gas, The tensile stress limits the appearance of two-dimensional free electron gas by reducing the carrier concentration at the interface and reducing its mobility. In the fifth chapter, we design a cellular structure of similar graphene, which is composed of heavy transition metals, to realize the Chen's insulation state. the destruction of the flutter makes it difficult to find a specific type of such an aging insulator, based on the previous 3d series of metal oxides, by adjusting the spin-orbit coupling (soc) and other interactions, we have designed two wide-band gap-gap insulators with a band gap of up to 132 mev, The results show that the balance of the SOC and the other effects will lead to a wider band gap, and the stronger SOC can lead to a larger Hall conductance, and the reduction of the symmetry caused by the structural optimization can also damage the formation of the quantum anomalous Hall effect. in these two robust chen-number insulators, all of the degrees of freedom are released, The structure still maintains high symmetry. The development of oxide film growth technology in recent years has also provided us with the possibility of this kind of insulator experiment. In chapter 6, we have made a brief summary of the work of this paper and the prospect of the future.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469
本文编号：2509333
[Abstract]:With the progress of science and technology, the performance of the computer is greatly improved, and people's understanding of the physics theory is more in-depth, and the computer simulation to explain the physical phenomena and the design of the functional materials has become an indispensable scientific research means. The density functional theory has a unique advantage in the precision and dependence on the empirical parameters, making it stand out in many of the first principle methods. Perovskite-oxide heterojunction has attracted many experimental and theoretical workers due to its interface and its surface-rich physical properties. Based on the first principle, we design and study the different kinds of perovskite-oxide heterostructures, including the prediction of the photocatalytic ability of the heterojunction, the control of the two-dimensional free electron gas of the interface, and the discovery of the topological properties of the heterojunction. The application of the perovskite-oxide heterojunction in the fields of physics, chemistry and electronics has been theoretically predicted and discussed. In that first chap, we introduce a general introduction to the detail of the theoretical calculation method. There are: Hartree-Fock method based on wave function; density functional theory based on electron density. The background and development of their theories are described in detail. Then, we introduce the most important and most important exchange-related general function in the density functional theory, and then briefly introduce two commonly used calculation software packages. In the second chapter, we introduce the most popular LaAlO3/ SrTiO3 (001) (LAO/ STO (001) interface in the last ten years, including the generation of two-dimensional free electron gas, the critical number of layers and three different mechanisms (polarization disaster model, oxygen defect model and ion exchange model). Then we make a brief introduction to the other strange physical phenomena of the interface, such as the ferromagnetism, the superconductivity and the ferrosuperconducting coexistent phenomenon of the interface. In the third chapter, a new transition-metal-oxide-heterojunction model is proposed, and a new kind of material for photocatalysis is designed. In this paper, we design a structured STO/ LAO/ STO (001) heterojunction with both n-type and p-type interfaces. Since the intrinsic electric field in the interior of the LAO (001) increases with the number of layers, we can adjust the energy band position of the STOs on both sides by changing the thickness of the LAO. By this method, the band gap of the system can be changed to the visible light or even the infrared light by changing the thickness of the LAO. At the same time, the electric field inside the LAO can move to the visible light or even the infrared light when the thickness of the LAO reaches a certain number of layers. At the same time, the electric field inside the LAO is separated and moved in the opposite direction, so that the two-dimensional free electron gas of the interface can be controlled by changing the lattice structure, and the stress is considered to be n-type LAO/ STO according to our calculation result. the compressive stress still increases the critical number of layers present in the two-dimensional free electron gas, The tensile stress limits the appearance of two-dimensional free electron gas by reducing the carrier concentration at the interface and reducing its mobility. In the fifth chapter, we design a cellular structure of similar graphene, which is composed of heavy transition metals, to realize the Chen's insulation state. the destruction of the flutter makes it difficult to find a specific type of such an aging insulator, based on the previous 3d series of metal oxides, by adjusting the spin-orbit coupling (soc) and other interactions, we have designed two wide-band gap-gap insulators with a band gap of up to 132 mev, The results show that the balance of the SOC and the other effects will lead to a wider band gap, and the stronger SOC can lead to a larger Hall conductance, and the reduction of the symmetry caused by the structural optimization can also damage the formation of the quantum anomalous Hall effect. in these two robust chen-number insulators, all of the degrees of freedom are released, The structure still maintains high symmetry. The development of oxide film growth technology in recent years has also provided us with the possibility of this kind of insulator experiment. In chapter 6, we have made a brief summary of the work of this paper and the prospect of the future.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469
【参考文献】
相关期刊论文 前1条
1 翁红明;戴希;方忠;;磁性拓扑绝缘体与量子反常霍尔效应[J];物理学进展;2014年01期
，本文编号：2509333
本文链接：https://www.wllwen.com/shoufeilunwen/jckxbs/2509333.html
