【作者】 李风平；

【导师】 戴瑛； 魏巍；

【作者基本信息】 山东大学 ， 原子与分子物理， 2020， 博士

【摘要】 硅基半导体的出现使得电子技术产品更加微型化和集成化,现如今研究者们在硅基半导体基础上石墨烯和相关二维材料进行了深入的研究和探索,进而推动了信息化产业的“二次革命”,也促进了二维材料在各行各业的应用和发展,使其成为下一代信息技术产业中最具有潜力的功能性材料。许多二维材料已经在实验上被成功合成和应用,并且理论上通过高性能的计算和模拟分析研究和预测了更多新型的二维功能性材料。基于石墨烯单层的类石墨烯材料具有超高载流子迁移率、费米速度以及量子霍尔效应,这些优异的性能推进了其在集成电路中的快速发展。除了寻找类石墨烯二维材料来丰富其光电子学、力学以及热力学的发展之外,通过对其维度的调控得到的低维纳米材料可以进一步应用在电化学以及储能方向上。但是对于类石墨烯二维材料的合成仍存在更多的挑战,并且对于其合成以后的物理化学性质的探究和机理分析也需要更进一步的探讨。此外,对于具有半导体性质的过渡金属硫族化合物组成的横向或者纵向的层状结构出现的新型的物理特性也更加丰富了二维材料在凝聚态物理学中的应用。更为有趣的是,二维材料在光电、光伏以及光催化系统中通过光电转化来提升太阳能利用率也发挥了不可多得的作用。与此同时,在这些光电器件中,光激发引起的激子效应对光电性质产生重要的影响,通过考虑激发态下的光物质相互作用可以为研究和设计新型光电器件提供更有价值的理论基础。除此之外,考虑受温度影响的晶格热力学振动产生的电子-声子耦合作用对二维材料中具有的激发态的玻色--爱因斯坦凝聚、激子相关的高温超导以及新型激子设备中的物理机制等具有指导性意义。因此,探究二维材料中光激发的光电性质对其内部物理化学性质的机理分析以及对光电器件的功能性调控也变得至关重要。在本论文中,我们通过第一性原理计算模拟分析了多种类石墨烯材料及其堆叠结构,并实现了对其电子结构和界面性质的调控,此外,我们也探究了二维材料堆叠结构的电子性质以及物理谷极化机制下的层间激子性质,并且进一步结合多体微扰理论探究了二维材料中的激发态光电性质以及考虑温度相关的电声耦合效应对激子效应的影响。论文分为六个章节:第一章简明论述了二维材料的研究现状和发展背景。第二章给出了本文中用到了理论计算方法和相关的计算软件介绍。第三章研究了类石墨烯材料生长界面的电子性质并通过降低维度对一维纳米管的电子性质进行了调控和对其储氢性能的探究。第四章探究了由极性MoSSe形成的范德华层状材料中具有的本征电场对其光电性质产生的影响。第五章深入的研究和讨论了在二维单层和双层材料中考虑温度和角度相关的激子效应。本论文的主要研究内容和结论如下:(1)通过第一性原理的计算模拟了与实验上相符合的锗烯单层生长在Au(111)衬底上的电子结构和界面性质。论证了锗烯与金属衬底之间较强的界面耦合作用,给出了锗烯单层由于对称性破坏之后其线性能带色散关系被打破的特征。另外,结合实验上成功制备的在Cu(111)衬底上生长的双层锗烯,理论分析了下层锗烯作为缓冲层可以用来减缓上层锗烯与金属衬底之间的电子轨道耦合强度,从而有利于上层锗烯的剥离和转移,其费米能级处的线性能带色散特征也可被较好的保存。综上所述,鉴于线性能带色散是新型量子现象的主要核心特征,对锗烯生长在金属衬底上的电子结构的分析有利于今后实验和理论上对类石墨烯二维单层的进一步的预测和分析,进而促进其在量子设备和光电器件中的应用。(2)构建和预测了三种新型的硼纳米管,并且通过对它们的手性和尺度的调控来讨论其电子性质的变化。通过对纳米管进行氢化,可以进一步稳定硼纳米管,而且在管的轴向施加应力可以实现金属到半导体性质的转变。其中对于两种特殊的含有孔状的硼纳米管,通过对其进行储氢性能的研究,发现具有良好的储氢能力,而且对其氢气和氢气之间以及氢气和硼纳米管之间的相互作用能以及吸附能的探究可以预测其具有更高的储氢率。故通过降低类石墨烯材料硼烯单层的维度,可以有效的实现对电子性质的调控并发掘其在储氢上的应用潜力。(3)讨论了极性MoSSe单层组成的范德华层状材料的光电性质。通过考虑电子-电子自能相关的GW近似,给出了极性MoSSe和WSSe单层的准粒子能带结构。通过对极性的MoSSe和WSSe组成的横向或者纵向的异质结构进行电子性质的研究,发现相对于单层MoSSe,纵向异质结具有的本征内建电场增强了 Rashba劈裂,而横向异质结构中的光响应明显提升。此外,横向或者纵向的异质结均构成了 II型能带对齐的特征,有利于层间或者界面激子的形成并产生较长寿命的谷极化激子。对于横向的MoSSe/WSSe,在构建不同的晶界的基础上,可以得到一维的金属界限,这也预示着在在这种异质构型中出现一维电子气的情况。以上对极性MoSSe单层的结构调控可以使其更好的应用在光电以及自旋电子学器件中。(4)探索了由MoSSe单层组成的范德华同质结中分别由面内和面外偶极矩诱导产生的Zeeman和Rashba劈裂。这类同质结中存在较大的层间能带位错,因此导致II型能带对齐特征的出现,并产生了具有较长谷极化寿命的层间激子,提升了光伏器件的使用效率。此外,由研究结构表明垂直偶极矩诱导产生的Rashba劈裂可以通过施加应力和调节层间距离来进行调控,并且我们也阐述了这种调控手段的物理机理。对由MoSSe单层组成的同质的范德华层状结构的电子性质的研究有助于对今后其在谷激子相关的物理学的理解以及在自旋电子学设备中的应用。(5)研究了极性MoSSe单层中的激发态光电性质。基于多体格林函数的微扰理论,论证了强的激发态性质会对MoSSe的光吸收性质产生重要影响,并且在低能位置具有较大的激子结合能。考虑到实际应用中的温度产生的热力学晶格振动的影响,也就是包含电子-声子耦合作用,其带隙在0 K时降低了 40meV。而且随着温度的升高,激子的位置、强度以及展宽也均受到了影响。理论计算得到温度相关的光学带隙可以与实验上室温下的光致发光光谱很好的对应。进一步,对于极性MoSSe也探究了其考虑含时的动力学下的激子的行为,结果表明其层内激子可以在一定时间尺度内进行快速结合。另外,通过考虑多体格林函数的激发态理论,探究了光入射角度的变化对于各向异性单层黑磷的光吸收的影响,通过考虑温度相关的准粒子态的激子寿命和展宽验证了黑磷中随温度升高而逐渐增加的准粒子带隙。我们对极性MoSSe和各向异性的黑磷中的激发态的光电性质和激子的动力学的讨论为在其它二维材料中的光物质相互作用的研究提供很好的理论基础,并且为探究由二维单层组成的范德华结构的激子效应在光电、光伏以及谷电子学上的应用提供了有利的理论指导。(6)探究了由不同过渡金属硫族化合物组成的层状材料的层间激子的产生机制。结合第一性原理计算和多体格林函数微扰理论以及含时的非绝热分子动力学的模拟计算,对具有不同层间内建电场的三种过渡金属硫族化合物的范德华双层的层间激子进行了理论分析。层间激子的产生可以从量子限制的Stark效应来解释。而且结果对比分析得出具有较大内建电场的MoSSe/WSSe的异质结具有相对更高的激子结合能、层间能带位错以及长的电子一空穴复合时间,这也就意味着其具有较高的光电转化效率和强的谷极化激子。我们对二维过渡金属硫族化合物的范德华双层结构的研究表明了通过结构调控层间激子的可行性,更多其它二维范德华材料中的激发态性质以及光物质相互作用的探究也会得到促进。更多还原

【Abstract】 The emergence of silicon-based semiconductors has made electronic technology products more miniature and integrated.Nowadays,the exploration and research of graphene and related two-dimensional materials has rapidly promoted its application and development in various industries,and has become the most potential functional materials in the next-generation information industry.Various two-dimensional materials have been successfully synthesized and applied experimentally,and theoretically,more novel two-dimensional functional materials have been analyzed and predicted through high-performance calculations and simulations.The two-dimensional graphene-like material based on graphene single layer has ultra-high carrier mobility,Fermi velocity and quantum Hall effect,promoting the development of integrated circuits.In addition to looking for graphene-like two-dimensional materials to enrich its development in optoelectronics,mechanics,and thermodynamics,low-dimensional nanotubes can be obtained by reducing their dimensions and hydrogenation can further promoting their use in electrochemical and energy storage.In addition,the new type of physical properties that appear after the horizontal or vertical layered structure composed of semi-conductive transition metal chalcogenides has further expanded the application of two-dimensional materials.More interestingly,two-dimensional materials have also played a rare role in improving the utilization of solar energy through photoelectric conversion in photoelectronic,photovoltaic,and photocatalytic systems.Therefore,investigating the photoelectric properties of photoexcitation in two-dimensional materials has become crucial to their internal mechanism analysis and functional regulation of optoelectronic devices.However,there are still more challenges in the synthesis of graphene-like two-dimensional materials,and further exploration of the electronic properties and mechanism analysis after synthesis is needed.At the same time,it is instructive to consider the interaction between electrons,phonons,and photons and the coupling between excitons and excitons in the practical application of two-dimensional materials.The consideration of the photo-matter interaction in the excited state can provide a more valuable theoretical basis for the research and design of new types of optoelectronic,photocatalytic,and photovoltaic devices.In this dissertation,We have simulated and analyzed a variety of graphene-like materials through first-principles calculations based on density functional theory and engineering their electronic structures and interface properties;explored interlayer excitons using stacked bilayer multilayer materials to investigate the physical valley polarization mechanism;and further explore the ground state and temperature-dependent electro-phonon coupling effects by combining many body perturbation theory to reveal the excited photoelectric properties.The thesis is mainly divided into six chapters.The first chapter briefly discusses the research status and development background of two-dimensional materials.The second chapter gives the theoretical calculation methods and related calculation software used in this paper.The third chapter introduces the investigation of the electronic properties of the interface effects of graphene-like material growth condition,and tunable electronic properties and energy storage application of one-dimensional nanotubes.Chapter 4 explores the optoelectronic properties of the van der Waals layered material formed by polar MoSSe.In Chapter 5 give and insight into the photoelectric properties of monolayer and bilayer materials considering temperature dependence.The main research contents and conclusions of this paper are as follows:(1)We study two-dimensional germanene supported on Au(111)to determine the structural,electronic and interface interaction properties on the basis of first-principles electronic calculations.The simulated configuration consistent with the experiment,The germanene on Au(111)loses its linear band dispersion relationship and demonstrates intense hybridization effects with Au(111).In addition,the structural and electronic properties of the recently synthesized monolayer and bilayer germanene on Cu(111)though first-principles calculations are studied.For bilayer germanene on Cu(111),interactions with Cu(111)are reduced due to germanene inter-layer interactions,which is beneficial for the transfer of germanene.In comparison with the bottom germanene layer,the Dirac cone character of the upper germanene layer can be maintained near the Fermi level.In summary,Since the linear band dispersion is at the heart of the novel quantum phenomenon,our results will facilitate research into the synthesis,extraordinary quantum properties,and optoelectric applications based on the two-dimensional graphene-like materials.(2)Three novel types of boron nanotubes were constructed and predicted,and their electronic properties were discussed by adjusting the chirality and diameters.By means of hydrogenating the nanotubes,stable nanotubes can be obtained.Moreover,applying stress in the axial direction of the tube can achieve the transition from metal to semiconductor.Among them,two special pore boron nanotubes have studied the hydrogen storage performance,and found that they have good hydrogen storage capacity,and the interaction between hydrogen and hydrogen or between hydrogen and boron nanotubes predict that it has better hydrogen storage capacity.Therefore,it can effectively regulate the electronic properties and explore its potential for hydrogen storage by lowering dimensional of the graphene-like borophene.(3)The optical and electrical properties of a vdW layered material consisting of a single layer of polar MoSSe are discussed.The quasi-particle band structure of polar MoSSe and WSSe monolayers is given by considering the GW approximation including electron-electron self-energy correlation,and its excited state has important research value for light response.By studying the electrical properties of the horizontal or vertical heterojunction composed of polar MoSSe and WSSe,it is found that the generation of its built-in electric field improves the polarization intensity of Rashba,and the response improved significantly compared to the monolayer.In addition,the horizontal or vertical heterojunctions form the type Ⅱband alignment,which is beneficial to the formation of interlayer excitons and the generation of long valley polarization excitons.For lateral MoSSe/WSSe,one-dimensional metal boundaries can be obtained on the basis of constructing different grain boundaries,which also indicates the occurrence of one-dimensional electron gas in this heterogeneous configuration.The above structure control of the polar MoSSe can make it commendable used in optoelectronics and spintronics devices.(4)The electronic properties of the Zeeman and Rashba splitting generated by in-plane and out-of-plane dipole moments in the homogeneous vdW bilayer and trilayers composed of MoSSe were explored.Results show that there are large band offsets in the vdW layered structure composed of MoSSe monolayers with intrinsic vertical dipole moments,which will also cause type-Ⅱ band alignment features.In this case,interlayer excitons with longer valley polarization lifetimes will appear,which provides better conditions for the practical application of photovoltaic devices.In addition,the strength of Rashba splitting due to the vertical dipole moment can be adjusted by applying stress and adjusting the interlayer distance,and we also give an explanation of the internal mechanism of this regulation.The study of the electronic properties of the homogeneous vdW layered structure composed of MoSSe will have potential application value for the future use of valley-related physics and spintronics devices.(5)The photoelectric properties of excited states in polar MoSSe monolayers were investigated.Based on the many body perturbation theory,it is demonstrated that the strong excited state properties will have an important effect on the optical absorption properties of MoSSe,and it has a large exciton binding energy at low energy positions.Considering the temperature effect in practical applications,that is,including the influence of electron-phonon coupling,the band gap is reduced by 40 meV at 0 K.And as the temperature rises,the position,intensity,and width of the excitons are also affected.The theoretically calculated temperature-dependent optical band gap can correspond well with the experimental photoluminescence spectrum at room temperature.Furthermore,for polar MoSSe,the behavior of excitons under the consideration of time-dependent dynamics was also investigated,and the results show that the intralayer exciton can be rapidly combined within a certain time scale.In addition,by considering the theory of excited states of the many body Green function,the dependent angle of light incidence on the light absorption of anisotropic single-layer black phosphorus was explored,and quasi-particle band gap show an increase tendency as temperature increase by considering the temperature-dependent quasiparticle state exciton lifetime and broadening.Our research on the photoelectric properties of the excited state for polar MoSSe,anisotropy black phosphorus and the dynamics of excitons provides a favorable theoretical guidance theoretical for the light-matter interaction in two-dimensional materials.(6)The interlayer excitons in vdW layered materials composed of different TMDCs was investigated.Combining first-principles calculations with many body Green’s function theory and time-dependent non-adiabatic molecular dynamics simulation,the interlayer excitons composed of three TMDCs vdW bilayers with different built-in electric fields were theoretical performed.Interlayer exciton generation can be explained by the quantum confined Stark effect.Moreover,the results of comparative analysis show that MoSSe/WSSe heterojunctions with large built-in electric fields have relatively higher exciton binding energy,larger band offset,and longer electron-hole recombination time,which means that it has high photoelectric conversion efficiency and strong valley polariton.Our results for 2D TMDCs vdW bilayers in particular show the great possibility of structural tunability to manipulate the interlayer excitonic properties and advance the excitonic devices,thus would drive more interesting studies on the excited-state properties and light-matter interactions of other 2D vdW materials.更多还原