碱土金属吸附二维α_1硼烯结构和性质研究

采用密度泛函理论系统计算和研究了碱土金属(铍、镁和钙)单原子、二聚体、双原子吸附新型二维α_1硼烯后众多可能的吸附点和吸附情况.通过体系总能量的计算,鉴定了不同吸附体系最稳定的几何构型,并对其稳定性进行了详细地分析和讨论.经研究发现单原子铍和镁最低吸附点是空心位,而钙是顶位附近.通过吸附能计算发现二聚体碱土金属吸附硼烯后体系的稳定性高于单原子情况,但低于双原子吸附,表明碱土金属原子倾向于孤立地吸附于各自最低能量吸附点,而不是以团簇形式吸附.通过电荷转移和态密度进一步分析和讨论了碱土金属原子与硼烯的相互作用和成键方式,发现碱土金属与硼烯之间同时具有离子键和共价键性质.     

一种新型二维材料:硼烯

硼烯是硼元素的二维同素异形体,其结构和物理特性一直受到研究者的强烈关注。但由于现实中缺乏天然存在的硼烯,该领域的研究只能停留在理论上的描述。最近,作者所在研究组成功地制备出了单层硼烯薄膜,实现了学术界期待已久的突破,并对其原子结构和电子性质进行了深入的研究,为未来研制基于硼烯的电子器件提供了潜在可能。文章将从硼烯的理论研究开始讲起,着重介绍该新型二维材料的结构模型、实验制备过程及其电子结构表征等研究。     

硼烯的实验制备

硼烯作为目前发现的最轻的二维材料,表现出丰富的物理性质,包括高柔韧性、光学透明性、高热导率、近一维自由电子气、狄拉克费米子、超导电性等.然而,由于体相硼的层间共价键结合力较强,很难剥离出单层硼烯.另外,硼原子的缺电子属性,使其化学性质比较活泼,成键复杂,导致硼烯有很多同素异形体.长期以来,关于硼烯的研究停留在理论探索方面,硼烯的实验制备一直难以突破,直到最近几年才由少数课题组成功制备,至此关于硼烯的生长、结构以及电子性质研究打开了巨大的探索空间.本文主要从实验方向,系统综述了硼烯在不同衬底上的制备方法以及表现的不同结构相,并讨论了其生长机理.硼烯的制备为进一步扩展硼烯的物理性质提供研究平台,为探索硼烯的纳米器件制备提供思路,使得其在高能量储备、光电子器件、高检测灵敏度、柔性纳米器件等方面具有巨大的潜在应用前景.     

超高真空条件下分子束外延生长的单层二维原子晶体材料的研究进展

二维原子晶体材料具有与石墨烯相似的晶格结构和物理性质,为纳米尺度器件的科学研究提供了广阔的平台.研究这些二维原子晶体材料,一方面有望弥补石墨烯零能隙的不足;另一方面继续发掘它们的特殊性质,有望拓宽二维原子晶体材料的应用领域.本文综述了近几年在超高真空条件下利用分子束外延生长技术制备的各种类石墨烯单层二维原子晶体材料,其中包括单元素二维原子晶体材料(硅烯、锗烯、锡烯、硼烯、铪烯、磷烯、锑烯、铋烯)和双元素二维原子晶体材料(六方氮化硼、过渡金属二硫化物、硒化铜、碲化银等).通过扫描隧道显微镜、低能电子衍射等实验手段并结合第一性原理计算,对二维原子晶体材料的原子结构、能带结构、电学特性等方面进行了介绍.这些二维原子晶体材料所展现出的优异的物理特性,使其在未来电学器件方面具有广阔的应用前景.最后总结了单层二维原子晶体材料领域可能面临的问题,同时对二维原子晶体材料的研究方向进行了展望.     

N、P掺杂硼烯/石墨烯异质结的密度泛函理论研究

采用基于密度泛函理论的第一性原理计算方法系统研究了氮、磷掺杂对硼烯/石墨烯异质结的几何结构和电子性质的影响.结果表明,相较完整硼烯/石墨烯异质结的金属特性,氮、磷掺杂的硼烯/石墨烯异质结均表现为半导体特性.室温下的分子动力学模拟进一步论证了相关体系的动力学稳定性.研究结果能够为硼烯/石墨烯异质结在新型二维半导体材料中的应用提供参考价值.     

低维限域结构中水与物质的输运

低维限域结构中水与物质的输运研究,对于解决界面化学和流体力学中的遗留问题十分关键.近年来,研究人员采用分子动力学模拟和实验手段研究低维限域结构中水与物质的输运,并将其应用于物质输运、纳米限域化学反应、纳米材料制备等领域.本文从理论和实验的角度总结一维和二维纳米通道的水与物质输运,介绍了本研究组提出的"量子限域超流体"概念,并用于解释纳米通道中超快物质的输运现象;在此基础上概述了一维纳米通道中的分子动力学模拟和水浸润性,以及外部环境(如温度和电压)对限域结构中水浸润性的调控,同时阐述了低维限域结构中的液体输运;对二维纳米通道中的分子动力学模拟、液体浸润性以及液体输运进行了综述;讨论了纳米通道限域结构在物质输运、纳米限域化学反应和纳米材料制备等领域的应用;对低维限域结构中水与物质输运面临的挑战和前景进行了展望.     

过渡金属硼化物的结构与性质

过渡金属硼化物(TMBs)是一类具有强耐磨性、抗腐蚀性、耐高温、高硬度的多功能材料.过渡金属与硼原子间电荷转移量的多样性决定了过渡金属硼化物中化学键的成键方式和成键强弱,最终导致过渡金属硼化物丰富的结构以及潜在的多功能特性.过渡金属硼化物的制备、晶体结构和力学性能一直是该领域的研究热点.硼原子间的强共价键决定了过渡金属硼化物的合成需要高能量;晶体结构中化学键的强弱与过渡金属硼化物的硬度性质息息相关;多种化学键成键方式使过渡金属硼化物展现出了丰富的多功能性质.本文主要从过渡金属硼化物的合成、结构、硬度性质和多功能性质四个方面,以不同硼原子亚结构单元为出发点,总结和分析了过渡金属硼化物的研究现状.我们认为,利用高温高压制备TMBs,诱导过渡金属与硼原子之间的电子转移,构造(准)三维的化学键,是设计制备新型多功能硬质过渡金属硼化物的有效方法.     

一维Ga2O3纳米材料及其光电导性能研究进展

一维纳米材料以其特殊的物理和化学性质成为了现在纳米材料研究的热点.目前国内对一维纳米材料研究主要体现在两方面：一是一维纳米材料的制备;二是纳米材料的功能器件研究,如光电探测器、气敏探测器等.本文综述了一维Ga2O3纳米材料的几种常用的制备方法,包括工艺参数及生长机理,并简单介绍了Ga2O3光电导探测器的工作原理及最近的研究成果.     

磷烯的研究进展与展望

黑磷晶体的单原子层结构被定义为磷烯，它具有独特的褶皱形态和一些区别于其它二维晶体材料的特性，如可调控的直接带隙，高开关比，高载流子迁移率以及优异的光学饱和吸收特性等，使其在纳米电子和纳米光学领域具有潜在应用价值.此外，蓝磷烯被理论计算所预测，它是黑磷烯的一种同素异形体，具有许多类似黑磷烯的优异特性.本文主要介绍了当前两种构型磷烯的研究进展，包括黑/蓝磷烯各自的晶体结构、制备方法、物理特性和稳定性；最后对目前磷烯研究中存在的问题与挑战提出了一些见解和展望.     

类石墨烯锗烯研究进展

近年来,伴随石墨烯研究的深入开展,考虑到兼容半导体工业,构筑类石墨烯锗烯并探究其奇特电学性质已成为凝聚态物理领域的研究前沿.本文首先简要介绍了锗烯这一全新二维体系的理论研究进展,包括锗烯的几何结构、电子结构及其调控以及它们之间的关系.理论研究表明,因最近邻原子间距大,锗烯比硅烯更难构筑,实验上构筑锗烯颇具挑战性.针对这一问题,介绍了实验上制备锗烯的一些进展,重点介绍了金属表面外延制备锗烯,并对本征锗烯的制备及其在未来纳电子学器件的潜在应用做出了展望.     

Review of thermal transport and electronic properties of borophene

In recent years, two-dimensional boron sheets(borophene) have been experimentally synthesized and theoretically proposed as a promising conductor or transistor with novel thermal and electronic properties. We first give a general survey of some notable electronic properties of borophene, including the superconductivity and topological characters. We then mainly review the basic approaches, thermal transport, as well as the mechanical properties of borophene with different configurations. This review gives a general understanding of some of the crucial thermal transport and electronic properties of borophene, and also calls for further experimental investigations and applications on certain scientific community.     

Versatile GaInO_3-sheet with strain-tunable electronic structure,excellent mechanical flexibility,and an ideal gap for photovoltaics

Due to many remarkable physical and chemical properties, two-dimensional(2D) nanomaterials have become a hot spot in the field of condensed matter physics. In this paper, we have studied the structural, mechanical, and electronic properties of the 2D GaInO_3 system by first-principles method. We find that 2D Ga InO_3 can exist stably at ambient condition. Molecular dynamic simulations show that GaInO_3-sheet has excellent thermal stability and is stable up to1100 K. Electronic structural calculations show that GaInO_3-sheet has a band gap of 1.56 eV, which is close to the ideal band gap of solar cell materials, demonstrating great potential in future photovoltaic application. In addition, strain effect studies show that the GaInO_3-sheet structure always exhibits a direct band gap under biaxial compressive strain, and as the biaxial compressive strain increases, the band gap gradually decreases until it is converted into metal. While biaxial tensile strain can cause the 2D material to transform from a direct band gap semiconductor into an indirect band gap semiconductor,and even to metal. Our research expands the application of the Ga InO_3 system, which may have potential application value in electronic devices and solar energy.     

Recent progress on borophene: Growth and structures

Boron is the neighbor of carbon on the periodic table and exhibits unusual physical characteristics derived from electron-deficient, highly delocalized covalent bonds. As the nearest neighbor of carbon, boron is in many ways similar to carbon, such as having a short covalent radius and the flexibility to adopt sp² hybridization. Hence, boron could be capable of forming monolayer structural analogues of graphene. Although many theoretical papers have reported finding two-dimensional allotropes of boron, there had been no experimental evidence for such atom-thin boron nanostructures until 2016. Recently, the successful synthesis of single-layer boron (referred to as borophene) on the Ag(111) substrate opens the era of boron nanostructures. In this brief review, we will discuss the progress that has been made on borophene in terms of synthetic techniques, characterizations and the atomic models. However, borophene is just in infancy; more efforts are expected to be made in future on the controlled synthesis of quality samples and tailoring its physical properties.     

Perfect Narrow-Band Absorber of Monolayer Borophene in All-Dielectric Grating Based on Quasi-Bound State in the Continuum

Borophene has the unique optical properties of two-dimensional materials and its own anisotropic characteristics. This work proposes a perfect narrow-band absorption structure to enhance the interaction of light with the monolayer borophene inserted into two different dielectric gratings. The structure efficiently improves absorption efficiency based on the quasi-bound states in the continuum (Q-BIC). The absorption characteristics are numerically simulated and theoretically analyzed by using the rigorous coupled-wave analysis (RCWA) method and the finite element method (FEM). The absorption efficiency of the monolayer borophene is high, up to 99.18% with a full-width at half maximum (FWHW) of 0.62 nm, achieving nearly perfect narrow-band absorption. Moreover, the mechanism of enhanced absorption of monolayer borophene is verified by the coupled mode theory (CMT), which indicates that the nearly perfect absorption is also derived from the critical coupling. At the same time, the influence of the thickness and width of the two layer dielectric structure on the absorption efficiency is theoretically analyzed. Furthermore, due to the anisotropic optical properties of the structure for TE and TM polarized light, a narrow-band polarization plate or sensor can be realized. The structure designed provides a new possibility to enhance the interaction between monolayer borophene and light.     

硼烯纳米带能带结构和态密度的第一性原理研究

基于密度泛函理论,采用第一性原理的方法计算H修饰边缘不同宽度硼稀纳米带的电荷密度、电子能带结构、总态密度和分波态密度。结果表明,硼烯纳米带的宽度大小影响着材料的导电性能,宽度5的硼烯纳米带是间接带隙简并半导体,带隙值为0.674 eV,而宽度7的硼烯纳米带却具有金属材料的性质。分波态密度表明,宽度5的硼烯纳米带的费米能级附近主要是由B-2s、2p电子态贡献,H-1s主要贡献于下价带且具有局域性,消除了材料边缘的不稳定性。宽度7的B-2p和H-1s电子态贡献的导带和价带处于主导地位,费米能级附近B-2p和H-1s电子态的杂化效应影响材料的整体发光性能。     

二维过渡金属硫族化合物中的缺陷和相关载流子动力学的研究进展

原子级厚度的单层或者少层二维过渡金属硫族化合物因其独特的物理特性而被寄希望成为下一代光电子器件的重要组成部分。然而,二维材料的缺陷在很大程度上影响着材料的性质。一方面,缺陷的存在降低了材料的荧光量子效率、载流子迁移率等重要参数,影响了器件的性能。另一方面,合理地调控和利用缺陷催生了单光子源等新的应用,因此,表征、理解、处理和调控二维材料中的缺陷至关重要。本文综述了二维过渡金属硫族化合物中的缺陷以及缺陷相关的载流子动力学研究进展,旨在梳理二维材料中的缺陷及其超快动力学与材料性能之间的关系,为二维过渡金属硫族化合物材料特性和高性能光电子器件的相关研究提供支持。     

Penta-P<Subscript>2</Subscript>X (X=C,Si) monolayers as wide-bandgap semiconductors: A first principles prediction

By means of density functional theory computations, we predicted two novel two-dimensional (2D) nanomaterials, namely P₂X (X=C, Si) monolayers with pentagonal configurations. Their structures, stabilities, intrinsic electronic, and optical properties as well as the effect of external strain to the electronic properties have been systematically examined. Our computations showed that these P₂C and P₂Si monolayers have rather high thermodynamic, kinetic, and thermal stabilities, and are indirect semiconductors with wide bandgaps (2.76 eV and 2.69 eV, respectively) which can be tuned by an external strain. These monolayers exhibit high absorptions in the UV region, but behave as almost transparent layers for visible light in the electromagnetic spectrum. Their high stabilities and exceptional electronic and optical properties suggest them as promising candidates for future applications in UV-light shielding and antireflection layers in solar cells.     

MgNi2Bi4弹性和电子性质的第一性原理研究

Bi基化合物因其奇异的结构和物化性质备受科研人员关注MgNi₂Bi₄是实验上合成的一种新型泡利顺磁性层状金属材料,弱的层间相互作用表明它可能是一种潜在的二维材料本文利用第一性原理计算研究了块体和单层MgNi₂Bi₄材料的弹性和电子性质,结果显示块体MgNi₂Bi₄是一种具有复杂费米面的非磁延展性金属.小的解离能表明在实验上可能可以制备得到单层MgNi₂Bi₄,进一步计算表明单层MgNi₂Bi₄仍为典型的金属材料.我们对MgNi₂Bi₄材料弹性和电子结构的计算和分析有助于未来对该材料的进一步研究.