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目录 contents

    摘要

    硼与其近邻元素碳一样形成sp2杂化,易形成复杂的多面体结构。硼烯是硼元素的二维同素异形体,研究者们对其结构和物化特性一直有着浓厚的研究兴趣。由于其制备技术难以突破,长期以来该领域的研究只停留在理论探索上。最近,在铜、银基底上生长出了单层硼烯薄膜,并对其原子结构和光电特性进行了深入研究,这些实验研究为未来研制基于硼烯的高性能电子器件奠定了良好基础。本文首先介绍硼烯的理论研究进展,然后着重介绍二维硼实验制备及其光电性能表征等研究,并对当前国际上二维硼薄膜实验研究进展进行了总结和展望。

    Abstract

    Boron, like its neighboring elemental carbon, forms sp2 hybrids, which tends to form complex polyhedral structures. Borophene is a two-dimensional allotrope of boron, and researchers have a strong interest in its structural and physicochemical properties. Since the preparation of borophene is very difficult, the study in this field has stayed on theoretical exploration for a long time. Recently, the boron monolayers has been successfully grown on Cu and Ag foils, and its atomic structure and photoelectric properties have also been systematically studied. These experimental studies have laid a good foundation for developing high-performance boron‑based nanodevices. The theoretical research progress of borophene is firstly introduced. The preparation and properties of two-dimensional boron are described. Finally, the current research progress of two-dimensional boron thin film is summarized.

    单元素二维材料由于结构简单、易于表征和调控,通过掺杂和改性可以发展出其他二维材料,因此有必要对此进行深入系统研究。目前,单元素的硅烯(silicene)、锗烯(germanene)、磷烯(phosphorene)、锡烯(stanene)和锑烯(antimonene)等,而这些二维材料由于层外平面屈曲,均不如石墨烯(graphene)那样能形成稳定的平面结构,因此硅烯、锗烯、锡烯和锑烯等材料在空气中易被氧化,应用于器件研究存在着较大挑[1]。黑磷是磷的一种稳定的同素异形体,可以解理出纳米级厚度的薄层,近年来有研究组实现了基于少数层黑磷的场效应管的制备,但由于原子级厚度的黑磷在空气中的稳定性较差,难以将单原子层黑磷制造出稳定可控的电子器[2]。这使得研究者们考虑寻找一种稳定可控的新型二维单元素材料以使其在下一代的电子器件上得以广泛应用。于是,元素周期表中碳的近邻、电子结构和潜在应用相似的硼元素开始被人们重新考虑。事实上,关于硼的研究早已开始,但由于二维硼实验制备技术难以突破,长期以来该领域的研究只停留在理论探索上,近年来二维硼材料被少数课题组成功制备,但其结构和性能仍有很大的探索空间。

    本文将从硼烯的理论研究开始,介绍二维硼材料的理论结构模型的发展历程,着重介绍了当前国际上二维硼薄膜实验制备及性能研究的进展;然后对二维硼具有不寻常的机械、电子、光学、化学特性及其潜在应用进行了概述;最后对其潜在应用进行了展望。

  • 1 硼烯的理论研究

    1

    硼(Boron,B)在元素周期表中位于金属和非金属之间,是化学性质最丰富的元素之一,最早起于19世纪被发现的一种类金属元[3]。由于硼与其他元素具有强的结合能力,它在自然界中仅以各种化合物的形式存在。硼作为碳的邻近元素,原子的基态电子层结构是[He]2s22p1,价电子数是3,但原子轨道数为4,所以硼的价电子数比其原子轨道数少一个,成键时价电子层无法被填充满,所以硼也可以像碳一样形成sp2杂化,因此硼原子通常形成多中心键,这种类型的键对体系的稳定性和电子性质起着决定性作用。硼原子的这种特殊的电子结构造成了硼的多面体特性,使其趋向于形成具有复杂多面体结构的物质。这是造成硼与碳的晶体结构及物理化学性质存在很大差异的根本原因。

    直到1909年才能够制备出纯度为99%的单质[4],目前知道至少有16 种同素异形体,它们均以B12正二十面体为基本结构单元,按不同的方式结合而[5],如图1所示。低维硼的化学和物理性质变得更加有趣,因为具有几个到几十个原子的硼簇平面或笼状结构,其与碳在构象和电子结构方面类似。随着富勒烯、碳纳米管等碳的低维结构的发现,有关硼的纳米结构的探索也形成了研究热潮。尽管近十年来实验一直在进行,如何使得硼原子组装成亚稳二维结构仍存在着极大挑战。为此,理论研[6,7]预测了使用金属如银和铜作基底,以提升硼片的表面多态能量退化和动力学引导增长。下面将详细论述有基底和无基底硼的理论研究:

    图1
                            B12结构以及硼的同素异形体

    图1 B12结构以及硼的同素异形体

    Fig.1 Structure of B12 and corresponding allotrope

    早期关于硼单层结构的理论计算可以追溯到1995 年,德国科学家Boustani[8]用从头计算的方法计算了小的硼团簇(Bnn=2~14)的结构和电子性质。Boustani总结得到了硼团簇的构造法则“Aufbau principle”——硼团簇以准平面的形式存在,并且包含两种基本结构单元——六角形(B7)或五角形(B6)的硼金字塔。1997年,Boustani[9]进一步提出以这些准平面结构的硼团簇为基础,按Aufbau principle对硼团簇进行扩展,发现基于五棱锥和六棱锥的结构单元可以构建出比较稳定的硼平面团簇以及硼纳米管等结构。Boustani的理论后来得到了其他工作的证实,2003年美国布朗大学王来生等[10,11,12]结合光电子能谱实验和理论计算确定出了B8B9B10B11B12B13B14B15B19等一系列硼团簇的结构,发现一系列结构与Aufbau principle相符,由此证明翘曲的三角形晶格的单层硼是可以稳定存在的。2005―2010年,3个课题[13,14,15]通过理论计算提出硼单层的结构是褶皱的三角形网格结构。2007年,Tang等[16]通过理论计算提出了几个由三角形晶格和六边形孔洞形成的混合结构硼纳米片模型,后被称为α-sheet,这种模型中所有硼原子均处于一个平面上,不存在翘曲,而且每个原子的能量比之前研究认为最稳定的带翘曲结构的三角形晶格还要低0.12 eV/atom,这一结果对二维硼可能的多态性开辟了一个更广阔的研究领域。后来,在Tang 工作的基础之上,Yakobson等[17]又通过计算发现了六角格子比较集中的两种能量比α-sheet更低的结构——g1/8-sheet和g2/15-sheet。曾晓成研究[18]通过粒子群优化(Particle-swarm optimization,PSO)算法全局搜索了一系列低能态二维硼结构,其中有两种结构也比α-sheet的能量更低,他们计算得到了一部分二维硼薄膜结构,如图2所示。理论研究者们将硼团簇外推到二维形式,逐步揭示了原子级厚度硼薄膜(硼烯)存在的可能形态。

    图2
                            通过PSO算法全局搜索的一系列低能二维硼结构

    图2 通过PSO算法全局搜索的一系列低能二维硼结构

    Fig.2 A series of low-energy two-dimensional boron structure-s searched globally by PSO algorithm

    上述这些理论计算基于真空中小的硼团簇,均是由三角形晶格和六边形孔洞组合而成的准平面结[16,17,19,20,21,22,23]。三角形硼单层是电子富余的,而在三角形晶格中周期性地引入六边形洞可以使体系的电子数达到平衡,从而提高体系的稳定性。所有这些硼单层都可以通过在三角形硼单层的基础上挖不同图案的六边形洞来构建并且可以用洞的密度η这个参数来描述。洞的密度定义为六边形孔洞的数目与原三角形硼单层中硼原子总数的比值。所有这些六边形和三角形混合的硼单层(ht-BS)都是平面结构的。

    另外一个是局域结构参数CN(Coordination numberk),用于描述硼原子的配位[18]。根据结构中硼原子的配位数及配位数种类的不同,二维硼结构可以分为以下5类:(1)类,CN=5,6;(2)类,CN=4,5,6;(3)类,CN=4,5;(4)类,CN=3,4,5;(5)类,单一配位数。对于α-sheet,它结构中硼原子的配位数为5和6,而六边形孔洞的密度为1/9。对于二维硼结构来说,当CN=3 时,对应的是与石墨烯一样的蜂窝结构,此时六边形孔洞的密度最大,等于1/3。而当CN=6 时,对应的是三角形晶格,六边形孔洞密度最小,为0。关于二维硼结构的稳定性也可以这样理解,由于硼相对于碳缺少一个电子,蜂窝结构的硼实际处于缺电子的状态,而三角形晶格的硼则富余电子。三角形晶格与蜂窝结构按一定比例混合后正好可以得到更稳定的二维硼结构,寻找最低能量结构成为随后的二维硼研究焦点之一。

    由于在三角形网格结构的硼平面中,六边形孔洞(HH,以V表示孔洞)的排列组合纷繁复杂,直接使用密度泛函理论(Density functional theory,DFT)方法进行计算每一个可能的结构是不现实的。Penev[17]处理硼片材作为赝合金B1-υVυ,其中HH浓度定义为υ = m/N,这里的m是超级单元中的HH的数量, N表示三角格子晶格位点。这种处理允许使用集群扩展方法用精确的DFT计算进行扩充以确定扩展系数Jx,然后更容易地探索二维硼的构型空间。所有计算出的对称不等价结构,其中二维硼显示出本质上的多态性,所有稳定的异构体都位于10%~15%的HH浓度范围内。特别是,υ1/8υ5/36表示比α-sheet稍微更稳定(υ = 1/9)。后来,采用不同的全局优化方法,更多的理论研[6-7,17,24‑25]进一步扩展了对新异构体的搜索。尽管基态与使用不同泛函的计算可能略有不同,他们的所有结果证实了二维硼的多形态性。

    与体相本身为层状的二维材料(例如石墨烯、h‑BN和MoS2)相比,二维硼在能量上远高于其所有三维形态。例如,α-sheet硼中每个原子的能量要比体相硼中每个原子高出400 meV。二维硼的热力学缺陷以及其固有的多态性导致了制备上的极大挑战。因此,理论研究者们在构建二维硼薄膜结构时开始考虑基底的影响。通过第一性原理计算,Yakobson课题组提出具有特定六边形洞密度的硼单层可以通过在金和银表面沉积硼原子来获得,也可以通过在富硼环境下饱和MgB2的硼面来获[25]。2013年,赵纪军课题[26]通过第一性原理计算预测了硼单层在Cu(111)表面上的外延生长。研究了Cu簇(111)上有利的几何结构和硼簇的相互作用机制,并发现HHs在二维簇的成核过程很容易发生,进一步支持了使用金属底物辅助二维硼生长的可能性。尽管金属衬底对于二维硼的生长是必需的,但考虑到硼烯对电荷掺杂的高结构敏感性,金属与硼相互作用可以改变其基态结[27,28,29]。由金属基体预先确定的二维硼结构将作为进一步研究这种材料的基础。因此,另一个基本问题是:什么样的结构会受到金属的青睐?最近,本课题[6]采用了簇扩展方法,包括明确的金属基底,同时仍然将硼-金属体系处理为由三角形硼晶格和HH组成的“二元合金”,两者都支撑在金属基底上。这种处理能够对化学气相沉积(Chemical vapor desposition,CVD)合成中常用的金属进行二维硼全面的第一性原理研究。结果表明,二维硼结构的稳定强烈地依赖于基底材料。具体而言,Ag,Cu和Ni将电子贡献给二维硼,并因此增加了HH浓度,其随着衬底提供的电势导致υ1/6结构的纳米片作为基态,这一趋势与石墨硼层可以作为金属二硼化物(0001)面上基态的事实一[30,31],其中来自金属层的电子转移到硼片上,使硼在电子上等同于碳。与之相对应的是,电子由Au从硼中吸取,从而将二维硼的基态向较小的υ值移动,并可以保持其在真空中的结构简并性。值得注意的是,Ag(111)已经被随后的实验所证[32,33]

  • 2 硼烯的实验制备

    2

    从2000年至2014年十几年间,大量工作报道了关于硼纳米线、少数层硼纳米管、团簇等低维硼材料的制备,直到2015年本课题组报道了第一个二维硼单[34]。随后,在理论预测的配合下,Mannix和吴克[32,33]两个实验组先后在Ag(111)表面上制备出硼烯。Mannix等人声称他们实验得到的硼烯是t-BS[32],而吴克辉课题组实验中得到的硼烯是ht-BS[33]。早先预测的硼纳米片均为金属[6,7]也得到实验证实,填补了二维材料中半金属石墨烯、绝缘体h-BN以及半导体性质的过渡族金属硫族化合物二维材料的空白。这些工[32,33]突出了理论上在合成新材料并揭示新的属性和现象方面的重要性。此外,探索硼烯多种多样的属性和潜在应用也是研究者们的兴趣所在。但是,在实际应用中,将硼烯从基底上剥离下来和受控合成高质量样品仍然存在着很大挑战。在此,笔者介绍了二维硼结构实验制备方面的新进展,特别关注了 CVD法制备的二维硼单层,并将其与以分子束外延法、液相剥离法制备的二维硼材料进行了相应的分析和比较。

  • 2.1 CVD法制备的二维硼薄膜

    2.1

    CVD法是把一种或几种含有构成薄膜元素的化合物、单质气体通入放置有基底的反应室中,借助气相化学反应在基体表面上沉积出固态薄膜的工艺技术。在最近的10年中,石墨烯的发现推动了其他二维材料的研究热潮,CVD技术也得到了快速发展,广泛地用于二维薄膜材料的制备。

    2015年,本课题组首次在实验上突破了二维硼单层的制[34]。在该实验中,硼和三氧化二硼粉末的混合物被加热,在温度升高至约为1 373 K下形成二硼二氧化物蒸气,然后通过H2作为载气将其输运到另一个温区的铜箔表面,在1 273 K的条件下在铜箔表面进行沉积,以此获得尺寸为厘米见方的硼纳米薄膜,如图3所示。生长在金属Cu基底上的硼薄膜,可以通过FeCl3溶液将Cu基底腐蚀掉,将薄膜转移至SiO2/Si表面或者Cu网等不同基底上,将薄膜转移至Cu网上后通过透射电子显微镜发现薄膜有高的结晶性。硼薄膜的结构由B12二十面体和B2哑铃组成(图3(c)),该结构中每个晶胞具有28个原子,属于正交晶系(a =5.054 Å,b = 5.620 Å,c =6.987 Å),空间群为Pnnm,它可以被看作由(B2)α+(B12)α-两个组成部分,由此电荷转移实现了平衡,从而可以在空气中稳定存在。

    图3
                            CVD法制备的硼单层

    图3 CVD法制备的硼单层

    Fig.3 Preparation of boron monolayer by CVD

    为了进一步证实所制得薄膜是二维硼单质,本课题组将在铜箔上的硼薄膜进行了拉曼和XPS表征,拉曼峰为618 cm-1与γ-B28的拉曼峰位一致;从XPS实验结果来看,除了Cu的特征峰以及由于大气污染造成的C1s 和O1s 特征峰外,笔者清楚地观察到了B1s 特征峰。体相硼单质的1s 特征峰一般位于189~190 eV,该薄膜B1s峰位在187.6 eV,与之前报道的单质硼峰位一致。通过UV / Vis吸收光谱法分析石英基底上的γ-B28薄膜的光学性质。在614 nm(声子能量2.05 eV)处观察到特征吸收峰,可归因于直接激子跃迁。根据(ahν2 = - Eg,获得相应的光学带隙(Eg,op)为2.25 eV,其中是相应的声子能量,a是吸光度。该值大于通过吸收光谱测量及第一性原理计算得出的体相的值(1.7 eV),这是由于薄层中存在强的量子限制效应使得薄膜的峰位发生蓝移。以514 nm波长激发的室温光致发光(Photoluminescence,PL)光谱图中出现了一个强的发射带,其中心为626 nm,半峰宽度约为22 nm。PL峰值可归因于自由激子的重组,其表示带隙值的较低边界。通过测试体相硼,获得了弱的684 nm处的发射峰。相对于体相硼,二维硼单层在PL光谱中发生了明显的蓝移约58 nm,这一现象可归因于单层中存在强烈的量子限制效应。将所制备的硼薄膜转移到了SiO2/Si表面,经过原子力显微镜表征了厚度约为0.8 nm,与单层γ-B28的厚度一致,并非此前理论预测的单原子层厚度的硼烯,而是继承了体相硼复杂结构的薄膜,这将对硼薄膜的理论预测产生重要启发。

    此外,本课题组在此基础上继续探索了以硼和三氧化二硼粉末的混合物为硼源前驱体,利用CVD法在其他金属基底上生长二维硼材料。比如在金属钼基底上,本课题组首次制备了厚度仅为6.48 nm的Mo3B大面积连续薄膜,如图4[35]。此外,第一原理计算显示超薄Mo3B薄膜是金属性的,由于其具有良好的导电性和丰富的活性,故位点非常有利于增强HER活性。测量结果表明,薄膜表现出极其优异的催化性能并具有出色的循环稳定性和良好的耐腐蚀性,这为二维硼材料的结构、物化特性研究拓宽了研究思路。

    图4
                            CVD法制备的Mo3B薄膜

    图4 CVD法制备的Mo3B薄膜

    Fig.4 Preparation of Mo3B thin films by CVD

  • 2.2 分子束外延法

    2.2

    分子束外延技术(Molecular beam epitaxy,MBE)是当前高质量单晶薄膜和纳米结构制备的一种非常重要的手段。基本原理是,在约1×10-10 Torr的超高真空条件下,通过加热蒸发源使具有一定动能的分子或原子沉积到干净的单晶衬底表面,发生吸附、迁移或和表面发生反应,以实现材料的外延生长。MBE实质上是一种非平衡生长过程,它是气相原子沉积到衬底表面变为固相的过程,是生长动力学和热力学相互作用的结果。分子束外延主要研究的是不同结构或不同材料的晶体和超晶格的生长。

    Guisinger[32]和Feng等[33]分别报道了以纯硼粉为硼源利用分子束外延法在Ag(111)上实现了单原子层硼烯的制备,如图5所示。通过电子束蒸发纯硼源直接将硼沉积到纯净的单晶Ag(111)表面,扫描隧道显微镜(Scanning tunnel microscope,STM)表征表明,单原子硼层不仅面积较大,而且根据沉积速率呈现出不同的形态相结构。高沉积速率增加了在STM图像中出现为周期性突出的原子链均匀相的覆盖度,降低沉积速率有利于形成由矩形晶格组成的扁平条状相。此外,提高温度可以将扁平相转变成具有周期性纳米级波纹的新条纹相。波状条纹在温度低于720 K时覆盖面积较小,但随着温度升高到约1 000 K,可以达到全覆盖。

    图5
                            利用分子束外延法制备硼薄膜

    图5 利用分子束外延法制备硼薄膜

    Fig.5 Boron thin films prepared by molecular beam epitaxy

    Feng等[33]在大约570 K的温度下生长的样品与Guisinger等[32]报道的扁平条纹相近似的具有平行原子行的矩形晶格,称为S1相。当温度升高到680 K时,形成一个由平行链组成的新相S2。当样品退火到650 K时,S1相也可以转变为S2相。该相也表现出平行的原子排列,但是交替出现更亮和更暗的部分以及比S1相更短的行间距。这些部分组成一个紧凑的“砖墙”模式,非常类似于Guisinger等人制作的样品均质阶段。角分辨电子能谱实验结果表明,以分子束外延生长法制备的硼烯均是金属态,两篇报道中所用的硼烯模型将条纹阶段的起伏特征解释为由于Ag(111)表面各向异性机械应力和化学结合力下,ν1/6(或β12)结构模型进行了重建。这几种结构从实验上证明了近期理论计算所提出的在金属基底上制备金属态的单原子层硼烯薄膜的理论预测。然而,该方法制备的硼烯一旦暴露于空气中就很容易被氧化,难以投入实际应用。

    类似地,最近,Wu等[36]利用分子束外延技术在Cu(111)表面上生长了硼烯,获得了大至100 μm2的大单晶畴。该晶体结构是一种新颖的三角形网络,其六边形空位的浓度为η=1/5。他们的实验数据与第一原理计算一起表明电荷转移耦合到衬底而没有显著的共价键合。这一工作为制造基于硼烯的器件奠定了基础,并证实了硼烯作为人造二维材料开发模型的理念。

  • 2.3 插层法

    2.3

    插层法是先将聚合物单体或无机盐类分散、插层进入层状体相片层之中,然后原位聚合或者加热,利用聚合时放出大量的热或高温克服体相片层间的作用力使其剥离,从而使体相材料剥离成片状薄膜的过程。2018年初,新加坡南洋理工大学Li等[37]利用插层剥离的方法成功宏量制备了硼薄膜。他们利用超声波辅助在二甲基甲酰胺(N,N-dimethylformamide,DMF)/异醇(Isopropanol,IPA)(1 mg·mL-1)中液相剥离硼薄膜,获得了平均粒径为2 μm的块状硼粉末。该方法剥离出来的硼薄膜厚度大多集中在1.8~4.7 nm之间,即4~11层,获得的硼薄膜晶体结构与体相保持一致。虽然这种液相剥离的方法让研究者们看到了硼烯宏量制备的曙光,但对于利用该方法制备的硼烯质量的控制方面还有待进一步实验探索。

    总之,制备大面积高质量的样品是将二维硼薄膜真正投入工业应用的一个先决条件,CVD方法仍是第一选择。但近年来通过CVD方法制备的硼大多数是无定形结构,或者是块状或者比较厚的[38,39,40]。通过分析它们的生长条件和前体,提出了几种可能有助于CVD合成硼烯的方案:(1)生长温度是CVD制备方法的第一要素,温度太高会使形核朝三维方向进行,要么就长出曲服的硼薄膜,温度太低又可能无法跨越结晶的能量壁垒而变成无定形的硼团[32]。因此,精确控制生长温度能在一定程度上促使二维而非三维形核。(2)前驱体的选择方面,最好的前驱体是纯硼,其他元素如氧、硼的加入可能钝化悬挂键而使得三维形核位点稳定,从而降低相应的形核能[33]。理论计算表明,前驱体中氧的存在可能是硼纳米薄膜屈服的原因之一。(3)原子级平整的金属基底是制备大面积硼膜的理想基底,粗糙表面可能由于表面反应区域增加而发生三维形核。

  • 3 硼薄膜的器件应用

    3

    在光电器件应用方面,二维硼结构的丰富性引起了科学界对于其电子传输性质研究的浓厚兴[41,42,43,44,45,46]。硼纳米管,尤其是那些卷成片状的纳米管,预计比碳纳米管更具导电[42,43]。这些结果表明,使用硼纳米管互连和未来纳米级器件中接触的可能性,避免了碳纳米管中电导率的手性依赖性难题。此外,硼的高温稳定性,也为其作为一种高温条件下的光电子器件应用提供了可能。Xu等[44]通过分解乙硼烷获得的硼纳米片用以制造均效应晶体管(Field effect transistor,FET)器件和光电子器件。场发射实验中的开启电场为3.6 V·μm-1,阈值电场为5.08 V·μm-1。如图6(a,b)所示,硼纳米片也具有很高的光敏性和快速的光响应,需要理论计算来探索二维硼片的潜在应用。

    图6
                            硼薄膜器件的理论和实验结果

    图6 硼薄膜器件的理论和实验结果

    Fig.6 Theoretical and experimental results of boron-based devices

    在高效能量转换器件方面,Wang等[45]通过在二维硼薄片中掺杂金属离子用作储氢材料,其储氢性能与石墨烯进行了比较。由于具有更多活性的表面,因此使得分子氢与硼纳米片的结合比石墨烯更强。本课题[35]用CVD法制备了Mo3B薄膜,并探索了在0.5 M H2SO4溶液中Mo箔上生长的超薄Mo3B的电催化制氢性能,如图7所示。该超薄膜在酸性溶液具有良好的稳定性,Tafel斜率为52 mV/dec,这一值是目前为止钼硼化物催化剂中报道的最小值。该薄膜呈现出小的Tafel斜率,阻抗小且具有良好的稳定性。

    在力学器件应用方面,Peng等[46]研究了α-硼片在应变条件下的力学性能,并预测了α-硼片面内刚度高(约为石墨烯的2/3)。模拟结果表明,α-硼片具有高强度的机械性能并具有高度的灵活性,可用于表面声波传感器。二维硼的轻质和优异的机械性能可用于设计先进的复合材料。一方面,二维硼在失效之前可承受较大的加载,其加载程度与石墨烯相当。另一方面,二维硼的反应活性有助于与主体基质共价键合,从而实现可控转移,当然这还需要大量实验探索。

    图7
                            超薄Mo3B薄膜的电催化性能

    图7 超薄Mo3B薄膜的电催化性能

    Fig.7 Electrocatalytic performance of ultrathin Mo3B film

  • 4 结 论

    4

    硼因其特殊的电子结构和多样的成键方式而具有复杂的晶体结构和化学性质。长期以来,理论界提出了许多二维硼的模型,近年来部分也得到了实验证实。尤其,用CVD方法有望使得硼二维材料得以广泛应用。后续应该致力于开发切实可行的样品制备方法和转移技术,以使二维硼在电子器件方面得以应用。总之,对于硼烯的研究还只是刚刚开始,随着对其研究的逐步深入,硼烯所具有的新奇的原子结构和奇特的物理性质将进一步被人们所了解,为基于硼烯的应用提供可能。

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    • 2

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    • 3

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    • 4

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      LIU Y Y, PENEV E S, YAKOBSON B I. Probing the synthesis of two‑dimensional boron by first-principles computations[J]. Angewandte Chemie—In-ternational Edition, 2013, 52(11):3156-3159.

    • 8

      BOUSTANI I. Structure and stability of small boron clusters. A density functional theoretical study[J]. Chemical Physics Letters, 1995, 240(1/2/3):135-140.

    • 9

      BOUSTANI I. New quasi‑planar surfaces of bare boron[J]. Surface Science, 1997, 370(2/3):355-363.

    • 10

      ZHAI H J, KIRAN B, LI J, et al. Hydrocarbon analogues of boron clusters-planarity aromaticity and antiaromaticity[J]. Nature Materials, 2003, 2(12): 827-833.

    • 11

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    • 12

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    • 13

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    • 14

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    • 15

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    • 16

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    • 17

      PENEV E S, BHOWMICK S, SADRZADEH A, et al. Polymorphism of two-dimensional boron[J]. Nano Letters, 2012, 12(5):2441-2445.

    • 18

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    • 19

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    • 20

      KIRAN B, BULUSU S, ZHAI H J, et al. Planar-to-tubular structural transition in boron clusters: B-20 as the embryo of single-walled boron nanotubes[J]. Pro-ceedings of the National Academy of Sciences of the United States of America, 2005, 102(4):961-964.

    • 21

      ROMANESCU C, HARDING D J, FIELICKE A, et al. Probing the structures of neutral boron clusters using infrared/vacuum ultraviolet two color ionization: B-11, B-16, and B-17[J]. The Journal of Chemical Physics, 2012, 137(1):014317.

    • 22

      PIAZZA Z A, LI W L, ROMANESCU C, et al. A photoelectron spectroscopy and AB initio study of B21(-): Negatively charged boron clusters continue to be planar at 21[J]. The Journal of Chemical Physics, 2012, 136(10):104310.

    • 23

      SERGEEVA A P, PIAZZA Z A, ROMANESCU C, et al. B-22(-) and B-23(-): All-boron analogues of anthracene and phenanthrene[J]. Journal of the American Chemical Society, 2012, 134(43): 18065-18073.

    • 24

      YU X, LI L L, XU X W, et al. Prediction of two-dimensional boron sheets by particle swarm optimization algorithm[J]. The Journal of Physical Chemistry C, 2012, 116(37):20075-20079.

    • 25

      LU H G, MU Y W, BAI H, et al. Binary nature of monolayer boron sheets from AB initio global searches [J]. The Journal of Chemical Physics, 2013, 138(2): 024701.

    • 26

      LIU H S, GAO J F, ZHAO J J. From boron cluster to two‑dimensional boron sheet on Cu(111) surface: Growth mechanism and hole formation[J]. Scientific Reports, 2013, 3:3238.

    • 27

      TANG H, ISMAIL‑BEIGI S. Self-doping in boron sheets from first principles: A route to structural design of metal boride nanostructures[J]. Physical Review B, 2009, 80(13):134113.

    • 28

      ZHANG Z H, SHIRODKAR S N, YANG Y, et al. Gate-voltage control of borophene structure formation [J]. Angewandte Chemie—International Edition, 2017, 56(48):15421-15426.

    • 29

      ZHAO Y F, BAN C M, XU Q A, et al. Charge-driven structural transformation and valence versatility of boron sheets in magnesium borides[J]. Physical Review B, 2011, 83(3):963-968.

    • 30

      SUEHARA S, AIZAWA T, SASAKI T. Graphenelike surface boron layer: Structural phases on transition-metal diborides (0001)[J]. Physical Re-view B, 2010, 81(8):085423.

    • 31

      QIN N, LIU S Y, LI Z, et al. First-principles studies for the stability of a graphene-like boron layer on CrB2(0001) and MoB2(0001)[J]. Journal of Physics: Condensed Matter, 2011, 23(22):225501.

    • 32

      MANNIX A J, ZHOU X F, KIRALY B, et al. Synthesis of borophenes: Anisotropic, two-dimension-al boron polymorphs[J]. Science, 2015, 350(6267):1513-1516.

    • 33

      FENG B J, ZHANG J, ZHONG Q, et al. Experimental realization of two-dimensional boron she-ets[J]. Nature Chemistry, 2016, 8(6):564-569.

    • 34

      TAI G A, HU T S, ZHOU Y G, et al. Synthesis of atomically thin boron films on copper foils[J]. Angewandte Chemie—International Edition, 2015, 54(51):15473-15477.

    • 35

      WANG X F, TAI G A, WU Z H, et al. Ultrathin molybdenum boride films for highly efficient catalysis of the hydrogen evolution reaction[J]. Journal of Mat-erials Chemistry A, 2017, 5(45):23471-23475.

    • 36

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    • 37

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    • 38

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    • 40

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台国安

机 构:南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

Affiliation:The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

角 色:通讯作者

Role:Corresponding author

邮 箱:taiguoan@nuaa.edu.cn

作者简介:作者简介:台国安,男,教授,博士生导师,全国优秀博士学位论文提名获得者,江苏省“六大人才高峰”高层次人才。主要研究方向:二维原子晶体材料和器件。已发表学术论文60余篇,其中SCI论文43篇,SCI他引1 200余次。主持国家自然科学基金3项,江苏省自然科学基金面上项目2项,以及教育部博士点基金、博士后特别资助基金等项目十余项。2011年教育部“高等学校科学研究优秀成果奖”自然科学奖一等奖(排名第六)。台国安,E-mail:taiguoan@nuaa.edu.cn。

伍增辉

机 构:

1. 南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

2. 南京航空航天大学材料科学与技术学院,南京,211106

Affiliation:

1. The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

2. College of Materials Science and Technology, Nanjing University of Aeronautics & Astronautics, Nanjing, 211106, China

胡廷松

机 构:

1. 南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

2. 南京航空航天大学材料科学与技术学院,南京,211106

Affiliation:

1. The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

2. College of Materials Science and Technology, Nanjing University of Aeronautics & Astronautics, Nanjing, 211106, China

王睿

机 构:

1. 南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

2. 南京航空航天大学材料科学与技术学院,南京,211106

Affiliation:

1. The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

2. College of Materials Science and Technology, Nanjing University of Aeronautics & Astronautics, Nanjing, 211106, China

侯闯

机 构:南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

Affiliation:The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

郝金钱

机 构:南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

Affiliation:The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

盛利航

机 构:南京航空航天大学航空学院机械结构力学及控制国家重点实验室,纳智能材料器件教育部重点实验室和纳米科学研究所,南京,210016

Affiliation:The State Key Laboratory of Mechanics and Control of Mechanical Structures, Laboratory of Intelligent Nano Materials and Devices of Ministry of Education and Institute of Nano Science, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, China

胥橙庭

角 色:中文编辑

Role:Editor

html/njhkht/201901002/alternativeImage/fecef2a5-1be3-4d6f-8ea7-1f134f3786d9-F001.jpg
html/njhkht/201901002/alternativeImage/fecef2a5-1be3-4d6f-8ea7-1f134f3786d9-F002.jpg
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图1 B12结构以及硼的同素异形体

Fig.1 Structure of B12 and corresponding allotrope

图2 通过PSO算法全局搜索的一系列低能二维硼结构

Fig.2 A series of low-energy two-dimensional boron structure-s searched globally by PSO algorithm

图3 CVD法制备的硼单层

Fig.3 Preparation of boron monolayer by CVD

图4 CVD法制备的Mo3B薄膜

Fig.4 Preparation of Mo3B thin films by CVD

图5 利用分子束外延法制备硼薄膜

Fig.5 Boron thin films prepared by molecular beam epitaxy

图6 硼薄膜器件的理论和实验结果

Fig.6 Theoretical and experimental results of boron-based devices

图7 超薄Mo3B薄膜的电催化性能

Fig.7 Electrocatalytic performance of ultrathin Mo3B film

image /

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  • 参考文献

    • 1

      MANNIX A J, KIRALY B, HERSAM M C, et al. Synthesis and chemistry of elemental 2D materials[J]. Nature Reviews Chemistry, 2017, 1(1):0014.

    • 2

      DOGANOV R A, O’FARRELL1 E C T, KOENIG S P, et al. Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere[J]. Nature Communcations,2015, 6:6647.

    • 3

      DAVY H. The bakerian lecture. An account of some new analytical researches on the nature of certain bodies, particularly the alkalies, phosphorus, sulphur, carbonaceous matter, and the acids hitherto undecompounded; with some general observations on chemical theory[J]. Philosophical Transactions of the Royal Society of London, 1809, 99:39-104.

    • 4

      WEINTRAUB E. Preparation and properties of pure boron[J]. Transactions of the American Electrochemical Society, 1909, 16:165-184.

    • 5

      OGANOV A R, SOLOZHENKO V L. Boron: A hunt for superhard polymorphs[J]. Journal of Superhard Materials, 2009, 31(5):285-291.

    • 6

      ZHANG Z H, YANG Y, GAO G Y, et al. Two-dimensional boron monolayers mediated by metal substrates[J]. Angewandte Chemie—International Edition, 2015, 54(44):13022-13026.

    • 7

      LIU Y Y, PENEV E S, YAKOBSON B I. Probing the synthesis of two‑dimensional boron by first-principles computations[J]. Angewandte Chemie—In-ternational Edition, 2013, 52(11):3156-3159.

    • 8

      BOUSTANI I. Structure and stability of small boron clusters. A density functional theoretical study[J]. Chemical Physics Letters, 1995, 240(1/2/3):135-140.

    • 9

      BOUSTANI I. New quasi‑planar surfaces of bare boron[J]. Surface Science, 1997, 370(2/3):355-363.

    • 10

      ZHAI H J, KIRAN B, LI J, et al. Hydrocarbon analogues of boron clusters-planarity aromaticity and antiaromaticity[J]. Nature Materials, 2003, 2(12): 827-833.

    • 11

      ZHAI H J, ALEXANDROVA A N, BIRCH K A, et al. Hepta- and octacoordinate boron in molecular wheels of eight- and nine-atom boron clusters: Observ-ation and confirmation[J]. Angewandte Chemie—International Edition, 2003, 42(48):6004-6008.

    • 12

      ALEXANDROVA A N, BOLDYREV A I, ZHAI H J, et al. All-boron aromatic clusters as potential new inorganic ligands and building blocks in chemistry[J]. Coordination Chemistry Reviews, 2006, 250(21/22):2811-2866.

    • 13

      EVANS M H, JOANNOPOULOS J D, PANTELIDES S T. Electronic and mechanical properties of planar and tubular boron structures[J]. Physical Review B, 2005, 72(4):045434.

    • 14

      KUNSTMANN J, QUANDT A. Broad boron sheets and boron nanotubes: An AB initio study of structural, electronic, and mechanical properties[J]. Physical Review B, 2006, 74(3):035413.

    • 15

      TANG H, ISMAIL‑BEIGI S. First-principles study of boron sheets and nanotubes[J]. Physical Review B, 2010, 82(11):15.

    • 16

      TANG H, ISMAIL‑BEIGI S. Novel precursors for boron nanotubes: The competition of two-center and three-center bonding in boron sheets[J]. Physical Review Letters, 2007, 99(11):115501.

    • 17

      PENEV E S, BHOWMICK S, SADRZADEH A, et al. Polymorphism of two-dimensional boron[J]. Nano Letters, 2012, 12(5):2441-2445.

    • 18

      WU X J, DAI J, ZHAO Y, et al. Two-dimensional boron monolayer sheets[J]. ACS Nano, 2012, 6(8): 7443-7453.

    • 19

      HUANG W, SERGEEVA A P, ZHAI H J, et al. A concentric planar doubly π-aromatic B19-cluster[J]. Nature Chemistry, 2010, 2(3):202.

    • 20

      KIRAN B, BULUSU S, ZHAI H J, et al. Planar-to-tubular structural transition in boron clusters: B-20 as the embryo of single-walled boron nanotubes[J]. Pro-ceedings of the National Academy of Sciences of the United States of America, 2005, 102(4):961-964.

    • 21

      ROMANESCU C, HARDING D J, FIELICKE A, et al. Probing the structures of neutral boron clusters using infrared/vacuum ultraviolet two color ionization: B-11, B-16, and B-17[J]. The Journal of Chemical Physics, 2012, 137(1):014317.

    • 22

      PIAZZA Z A, LI W L, ROMANESCU C, et al. A photoelectron spectroscopy and AB initio study of B21(-): Negatively charged boron clusters continue to be planar at 21[J]. The Journal of Chemical Physics, 2012, 136(10):104310.

    • 23

      SERGEEVA A P, PIAZZA Z A, ROMANESCU C, et al. B-22(-) and B-23(-): All-boron analogues of anthracene and phenanthrene[J]. Journal of the American Chemical Society, 2012, 134(43): 18065-18073.

    • 24

      YU X, LI L L, XU X W, et al. Prediction of two-dimensional boron sheets by particle swarm optimization algorithm[J]. The Journal of Physical Chemistry C, 2012, 116(37):20075-20079.

    • 25

      LU H G, MU Y W, BAI H, et al. Binary nature of monolayer boron sheets from AB initio global searches [J]. The Journal of Chemical Physics, 2013, 138(2): 024701.

    • 26

      LIU H S, GAO J F, ZHAO J J. From boron cluster to two‑dimensional boron sheet on Cu(111) surface: Growth mechanism and hole formation[J]. Scientific Reports, 2013, 3:3238.

    • 27

      TANG H, ISMAIL‑BEIGI S. Self-doping in boron sheets from first principles: A route to structural design of metal boride nanostructures[J]. Physical Review B, 2009, 80(13):134113.

    • 28

      ZHANG Z H, SHIRODKAR S N, YANG Y, et al. Gate-voltage control of borophene structure formation [J]. Angewandte Chemie—International Edition, 2017, 56(48):15421-15426.

    • 29

      ZHAO Y F, BAN C M, XU Q A, et al. Charge-driven structural transformation and valence versatility of boron sheets in magnesium borides[J]. Physical Review B, 2011, 83(3):963-968.

    • 30

      SUEHARA S, AIZAWA T, SASAKI T. Graphenelike surface boron layer: Structural phases on transition-metal diborides (0001)[J]. Physical Re-view B, 2010, 81(8):085423.

    • 31

      QIN N, LIU S Y, LI Z, et al. First-principles studies for the stability of a graphene-like boron layer on CrB2(0001) and MoB2(0001)[J]. Journal of Physics: Condensed Matter, 2011, 23(22):225501.

    • 32

      MANNIX A J, ZHOU X F, KIRALY B, et al. Synthesis of borophenes: Anisotropic, two-dimension-al boron polymorphs[J]. Science, 2015, 350(6267):1513-1516.

    • 33

      FENG B J, ZHANG J, ZHONG Q, et al. Experimental realization of two-dimensional boron she-ets[J]. Nature Chemistry, 2016, 8(6):564-569.

    • 34

      TAI G A, HU T S, ZHOU Y G, et al. Synthesis of atomically thin boron films on copper foils[J]. Angewandte Chemie—International Edition, 2015, 54(51):15473-15477.

    • 35

      WANG X F, TAI G A, WU Z H, et al. Ultrathin molybdenum boride films for highly efficient catalysis of the hydrogen evolution reaction[J]. Journal of Mat-erials Chemistry A, 2017, 5(45):23471-23475.

    • 36

      WU R T, DROZDOV I K, ELTINGE S, et al. Large-area single-crystal sheets of borophene on Cu(111) surfaces[J]. Nature Nanotechnology, 2019, 14 (1):44-49.

    • 37

      LI H L, JING L, LIU W W, et al. Scalable production of few-layer boron sheets by liquid-phase exfoliation and their superior supercapacitive performa-nce[J]. ACS Nano, 2018, 12(2):1262-1272.

    • 38

      OTTEN C J, LOURIE O R, YU M F, et al. Crystalline boron nanowires[J]. Journal of the Amer-ican Chemical Society, 2002, 124(17):4564-4565.

    • 39

      BELLOTT B J, NOH W, NUZZO R G, et al. Nanoenergetic materials: Boron nanoparticles from the pyrolysis of decaborane and their functionalisation [J]. Chemical Communications, 2009, 22:3214-3215.

    • 40

      GE L H, LEI S D, HART A H C, et al. Synthesis and photocurrent of amorphous boron nanowires[J]. Nanotechnology, 2014, 25(33):335701.

    • 41

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