Low-frequency interlayer vibration modes in two-dimensional layered materials

摘要

Two-dimensional (2D) layered materials have been attracted tremendous research interest because of their novel photoelectric properties. If a single atomic layer instead of individual atoms is taken as a rigid motion object, two unique interlayer vibrations, i.e. compression/breathing and shear motions, at ultra low frequencies can be expected and actually have been observed in many layered materials. The vibrations stem from the interlayer van der Waals interaction and can be well described by a conventional linear-chain model in most cases. The vibration frequencies strongly depend on layer thickness, which enables an accurate determination of layer numbers. A quick and nondestructive determination of flake thickness is particularly important for the materials, since the physical properties can be dramatically changed in the cases of several atomic layers. As a measure of interlayer coupling, the low-frequency modes are also sensitive to the stacking methods of atomic layers and the overlapping of different kinds of 2D materials. This allows the modes to play a key role in the applications like van der Waals heterojunctions. In this paper, we will give a brief review on the experimental observations and theoretical understanding of the interlayer modes in several typical 2D systems, as well as their actual and potential applications. (C) 2016 Elsevier B.V. All rights reserved.