Geballe Laboratory for Advanced Materials, Stanford University , Stanford, California 94305, United States.
Acc Chem Res. 2015 Jan 20;48(1):81-90. doi: 10.1021/ar5003297. Epub 2015 Jan 2.
Electron occupation of orbitals in two-dimensional (2D) layered materials controls the magnitude and anisotropy of the interatomic electron transfer and exerts a key influence on the chemical bonding modes of 2D layered lattices. Therefore, their orbital occupations are believed to be responsible for massive variations of the physical and chemical properties from electrocatalysis and energy storage, to charge density waves, superconductivity, spin-orbit coupling, and valleytronics. Especially in nanoscale structures such as nanoribbons, nanoplates, and nanoflakes, 2D layered materials provide opportunities to exploit new quantum phenomena. In this Account, we report our recent progress in the rational design and chemical, electrochemical, and electrical modulations of the physical and chemical properties of layered nanomaterials via modification of the electron occupation in their electronic structures. Here, we start with the growth and fabrication of a group of layered chalcogenides with varied orbital occupation (from 4d/5d electron configuration to 5p/6p electron configuration). The growth techniques include bottom-up methods, such as vapor-liquid-solid growth and vapor-solid growth, and top-down methods, such as mechanical exfoliation with tape and AFM tip scanning. Next, we demonstrate the experimental strategies for the tuning of the chemical potential (orbital occupation tuned with electron filling) and the resulting modulation of the electronic states of layered materials, such as electric-double-layer gating, electrochemical intercalation, and chemical intercalation with molecule and zerovalence metal species. Since the properties of layered chalcogenides are normally dominated by the specific band structure around which the chemical potential is sitting, their desired electronic states and properties can be modulated in a large range, showing unique phenomena including quantum electronic transport and extraordinary optical transmittance. As the most important part of this Account, we further demonstrate some representative examples for the tuning of catalytic, optical, electronic, and spintronic properties of 2D layered chalcogenides, where one can see not only edge-state induced enhancement of catalysis, quantum Aharonov-Bohm interference of the topological surface states, intercalation modulated extraordinary transmittance, and surface plasmonics but also external gating induced superconductivity and spin-coupled valley photocurrent. Since our findings reflect the critical influences of the electron filling of orbital occupation to the properties in 2D layered chalcogenides, we thus last highlight the importance and the prospective of orbital occupation in 2D layered materials for further exploring potential functionalized applications.
电子占据二维（2D）层状材料中的轨道控制着原子间电子转移的大小和各向异性，并对 2D 层状晶格的化学成键模式产生关键影响。因此，它们的轨道占据被认为是电化学催化和能量存储、密度波、超导、自旋轨道耦合和谷电子学等物理和化学性质发生巨大变化的原因。特别是在纳米结构如纳米带、纳米板和纳米片中，二维层状材料为开发新的量子现象提供了机会。在本报告中，我们报告了通过改变电子结构中的电子占据来合理设计和化学、电化学及电学调节层状纳米材料的物理和化学性质方面的最新进展。在这里，我们首先从具有不同轨道占据（从 4d/5d 电子构型到 5p/6p 电子构型）的一组层状硫族化物的生长和制备开始。生长技术包括自上而下的方法，如气相-液相-固相生长和气相生长，以及自下而上的方法，如胶带机械剥离和原子力显微镜针尖扫描。接下来，我们展示了调谐化学势（通过电子填充调谐轨道占据）和由此调谐层状材料的电子态的实验策略，例如双电层门控、电化学嵌入和分子和零价金属物种的化学嵌入。由于层状硫族化物的性质通常由围绕化学势的特定能带结构决定，因此它们所需的电子态和性质可以在很大范围内进行调制，显示出独特的现象，包括量子电子输运和非凡的光透射率。作为本报告的最重要部分，我们进一步展示了一些代表性的例子，用于调谐二维层状硫族化物的催化、光学、电子和自旋电子性质，其中不仅可以看到边缘态诱导的催化增强、拓扑表面态的量子 Aharonov-Bohm 干涉、嵌入调制的非凡透光率和表面等离子体，还可以看到外部门控诱导的超导和自旋耦合谷光电流。由于我们的发现反映了轨道占据的电子填充对二维层状硫族化物性质的关键影响，因此最后强调了二维层状材料中轨道占据的重要性和前瞻性，以进一步探索潜在的功能化应用。
