Inoshita Takeshi, Saito Susumu, Hosono Hideo
Materials Research Center for Element Strategy Tokyo Institute of Technology 4259 Nagatsuta Kanagawa 226-8503 Japan.
Research Center for Functional Materials National Institute for Materials Science Tsukuba Ibaraki 305-0044 Japan.
Small Sci. 2021 Jul 17;1(9):2100020. doi: 10.1002/smsc.202100020. eCollection 2021 Sep.
Over the last half century, layered materials have been at the forefront of materials science, spearheading the discovery of new phenomena and functionalities. Certain layered materials are known to possess electronic states unassociated with any of the constituent atoms, having a large proportion of their probability amplitude in the space between the layers. Usually, such a nucleus-free interlayer state has energy above the Fermi level and is unoccupied. However, the energy decreases when cations are intercalated and may cross the Fermi level, as in the case of CCa, a superconductor with a of 11.5 K. A major thrust to the research of interlayer electrons comes with the discovery of layered electrides, which are alternating stacks of positively charged ionic layers and negatively charged sheets of electrons in the interlayer space. When intercalation compounds and layered electrides are thinned down to the atomic scale, the interlayer states survive as surface states floating over the surface. This review provides a unified overview of the two classes of materials hosting interlayer floating electrons near the Fermi level, intercalation compounds and layered electrides, and their properties, including high electron mobility, low work function, ultralow interlayer friction, superconductivity, and plasmonic properties.
在过去的半个世纪里，层状材料一直处于材料科学的前沿，引领着新现象和新功能的发现。已知某些层状材料具有与任何组成原子都无关的电子态，其概率振幅的很大一部分存在于层间空间。通常，这种无核层间态的能量高于费米能级且未被占据。然而，当阳离子插入时能量会降低，并且可能穿过费米能级，就像超导转变温度为11.5 K的CCa这种情况。层状电子化物的发现为层间电子的研究带来了重大推动，层状电子化物是由带正电的离子层和层间空间中带负电的电子片交替堆叠而成。当插层化合物和层状电子化物被减薄到原子尺度时，层间态作为漂浮在表面的表面态得以保留。本综述对两类在费米能级附近存在层间漂浮电子的材料，即插层化合物和层状电子化物，及其性质进行了统一概述，这些性质包括高电子迁移率、低功函数、超低层间摩擦力、超导性和等离子体性质。
