鈣鈦礦金屬氧化物異質結的第一性原理研究
發(fā)布時間：2019-07-03 10:53
【摘要】：隨著科技的進步,計算機性能得到了飛速的提高,人們對物理理論的認識也更加的深入,利用計算機模擬解釋物理現(xiàn)象以及設計功能材料已經(jīng)成為不可或缺的科研手段。由于密度泛函理論在精度以及對經(jīng)驗參數(shù)的依賴性上具有獨特的優(yōu)勢,使得它在眾多第一性原理方法中脫穎而出。鈣鈦礦氧化物異質結由于其界面以及表面豐富的物理性質而吸引眾多實驗和理論工作者的眼光,近十年來成為物理化學界爭相研究的熱點。本文我們主要通過第一性原理計算,對不同種類的鈣鈦礦氧化物異質結在理論上進行設計和研究,涉及的內(nèi)容包括對異質結光催化能力的預測,對界面二維自由電子氣的調控,和對異質結拓撲性質的發(fā)現(xiàn)。對鈣鈦礦氧化物異質結在物理、化學以及電子器件方面的應用作出了理論上的預測和機理上的闡述。第一章中我們對理論計算方法細節(jié)做一個概括性的介紹。有：基于波函數(shù)的Hartree-Fock方法；基于電子密度的密度泛函理論。對它們的理論背景和發(fā)展做了詳細的介紹。隨后,我們對密度泛函理論中最重要最核心的交換關聯(lián)泛函作了介紹,最后簡單介紹了兩個常用的計算軟件包。第二章中我們對近十年來最熱門的LaAlO3/SrTiO3(001)(LAO/STO(001))界面作了背景介紹,包括最受關注的界面二維自由電子氣的產(chǎn)生,臨界層數(shù)問題以及三種不同的機制(極化災難模型、氧缺陷模型和離子交換模型)。隨后我們對界面其他奇異的物理現(xiàn)象作了簡單的介紹,如界面的鐵磁性、超導性以及鐵磁超導共存現(xiàn)象。第三章中,我們通過計算,提出了新的過渡-金屬氧化物-異質結模型,設計出一種新型的用于光催化的材料。我們設計了一種既包含n型又包含p型界面的‘三明治”結構STO/LAO/STO(001)異質結。由于LAO(001)內(nèi)部存在的本征電場隨層數(shù)而增加,我們可以通過改變LAO的厚度來調節(jié)兩邊STO的能帶位置。通過這種方法,體系的帶隙有了明顯變小,從而大大提高了光吸收效率,通過第一性原理計算的結果看到,當LAO厚度到達一定層數(shù)后,光吸收范圍可移動至可見光甚至紅外光。同時,LAO內(nèi)部的電場將光激發(fā)的電子空穴對分離并向相反方向移動,有效地阻止了電子空穴對的復合,使得兩邊的STO分別成為電子摻雜和空穴摻雜的表面,在空間上分離了水的氧化還原反應。第四章中我們研究了應力是如何通過改變晶格結構來調控界面的二維自由電子氣。根據(jù)我們的計算結果,我們認為應力對于n型LAO/STO界面體系的二維自由電子氣具有重要的調控作用,通過應力引起的STO部分的鐵電性與LAO本征的電場的相互作用,調節(jié)STO的鐵電方向來“打開”和“關閉”界面二維自由電子氣。在壓縮應力情況下,我們提出的三種模型‘'para"、"up"、"down",其中“up”類型是“打開”二維自由電子氣的按鈕,‘'down"則是”關閉”按鈕,而對于"para"型,壓縮應力仍然提高了二維自由電子氣出現(xiàn)的臨界層數(shù),拉伸應力則通過減小界面處載流子濃度以及降低其遷移率來限制二維自由電子氣的出現(xiàn)。第五章中我們通過設計由較重的過渡金屬組成的類似石墨烯的蜂窩狀結構(honeycomb)來實現(xiàn)陳絕緣態(tài)。對稱性破缺導致拓撲性的被破壞,使得尋找一種具體的此類陳絕緣體成為難點,基于之前3d系列金屬氧化物的研究,我們通過調節(jié)自旋軌道耦合(SOC)以及其它相互作用,設計出兩種寬帶隙的陳絕緣體,帶隙高達132meV,其陳數(shù)分別是C=-1及C=2。通過這個研究我們發(fā)現(xiàn),SOC與其它作用的相互平衡將導致更寬的帶隙,而更強的SOC會引起更大的霍爾電導。而通過結構優(yōu)化而引起的對稱性降低也會破壞量子反�；魻栃男纬�,在這兩個具有魯棒性的陳數(shù)絕緣體中,放開所有自由度優(yōu)化過后,結構依然保持著較高的對稱性。近年來發(fā)展的氧化物薄膜生長技術也給我們提供了這種絕緣體實驗上的可能性。第六章中我們對本文的工作做了簡單的總結和對未來的展望。
[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.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O469
本文編號：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.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O469
【參考文獻】
相關期刊論文 前1條
1 翁紅明;戴希;方忠;;磁性拓撲絕緣體與量子反常霍爾效應[J];物理學進展;2014年01期
，本文編號：2509333
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