Honeycomb boron: alchemy on aluminum pan?
Honeycomb boron: alchemy on aluminum pan?
复制标题
DOI：
10.1016/j.scib.2018.02.019
复制
发表时间：
2018-02
期刊：
影响因子：
18.9
通讯作者：
S. Shirodkar;E. Penev;B. Yakobson
中科院分区：
文献类型：
--
作者：
S. Shirodkar;E. Penev;B. Yakobson
硼（B）是元素周期表（和拉丁字母表）中碳的一个缺电子邻居，与C相比，它的化学性质截然不同。这导致了硼的丰富的同素异形，这可以从其多个体相、不同的簇、笼状富勒烯、一维纳米管和二维（2D）片的可能性中看出。简而言之，B和C在其结构和电子性质方面具有非常小的相似性;尽管对于其中之一，2D蜂窝状片材看起来与最终的碳同素异形体-石墨烯同构。这个结构在本期《科学》杂志上有报道。Bull. by Li et al. [1]形成在每个家庭都熟悉的支撑物--铝锅上。2D硼（boron）本身表现出丰富的多晶型[2，3]，而蜂窝（）结构只是众多其他形式之一。蜂窝状硼（B）晶格已经被已知几十年，金属二硼化物是一个突出的例子[4]。然而，B只是在新千年的边缘才成为人们关注的焦点，因为在MgB 2中发现了显着的高Tc常规超导性[5]。然而，MgB 2中的B亚晶格紧紧地夹在Mg层之间，作为块体晶体的组成部分。快进到石墨烯时代，具有单原子蜂窝结构的无带隙半导体被分离出来[6]，并在电子的费米能级上显示出狄拉克锥。狄拉克电子的行为类似于无质量的费米子，赋予特殊的性质，如极高的电子迁移率，量子霍尔效应，克莱因隧道效应和伪磁效应的出现。这产生了广泛的应用，例如生物传感器、纳米电子学、纳米等离子体、光电子学、霍尔效应传感器，仅举几例，并有可能实现器件的急剧小型化。与石墨烯不同的是，在B中，狄拉克点远高于费米能级，这使得人们对石墨烯奇异行为的希望破灭。因此，能否将B分离成2D薄片的问题变得越来越有趣，重新点燃了将硼氢化物转化为石墨烯、将B转化为C的现代“炼金术”竞赛。从MgB 2 [7]、石墨烯的电子结构和2D B多晶型物[3]的能量学中吸取的教训可能指向答案。在石墨烯中，狄拉克点位于费米能级，在B中远高于费米能级，而MgB 2是中间情况。由Mg提供给B的电子使费米能级更靠近MgB 2中的B亚晶格的狄拉克锥，接近
Boron (B), the one-electron-lacking neighbor of carbon in the periodic table (and in the Latin alphabet), is identified by rather different chemistry as compared to C. This gives rise to rich allotropy of boron, which is seen in the possibility of its multiple bulk phases, diverse clusters, cage-like fullerenes, one-dimensional nanotubes and two-dimensional (2D) sheets. In brief, B and C have very little similarity in their structural and electronic properties; albeit for one, the 2D honeycomb sheet which appears isomorphic to the ultimate carbon allotrope–graphene. And this very structure, reported in this issue of Sci. Bull. by Li et al.[1], forms on a support familiar in every household—an aluminum pan. 2D boron (borophene) exhibits rich polymorphism itself [2, 3], and the honeycomb () structure is only one of the multitude of other forms. Honeycomb boron (B) lattice has been known for decades, with metal diborides being a prominent example [4]. Yet, B came into the limelight only at the brink of the new millennium with the discovery of remarkably high-Tc conventional superconductivity in MgB2 [5]. The B sublattice in MgB2 is, however, tightly sandwiched between Mg layers, as an integral part of the bulk crystal.Fast forward to the graphene era, a gapless semiconductor with monoatomic honeycomb structure was isolated [6] and displayed the Dirac cones at the Fermi level of electrons. The Dirac electrons which behave like massless fermions, impart exceptional properties such as extremely high electron mobility, emergence of quantum Hall effect, Klein tunneling and pseudomagnetic effects. This gives rise to a wide range of applications, such as biosensors, nanoelectronics, nanoplasmonics, optoelectronics, Hall-effect sensors, to name a few, with the promise of a drastic miniaturization of devices. Unlike graphene, in B the Dirac points lie far above the Fermi level, fading the hopes for graphene-like exotic behavior. Thus, the question of whether B can be isolated into a 2D sheet has become ever more intriguing, rekindling a modern-day “alchemy” contest for converting borophene into graphene, B into C. The lessons learned from the electronic structure of MgB2 [7], graphene, and the energetics of 2D B polymorphs [3] may point to the answer. The Dirac point is at the Fermi level in graphene, well above it in B, while MgB2 is an intermediate case. The electrons donated by Mg to B shift the Fermi level closer to the Dirac cones of the B sublattice in MgB2, approaching the