title: Interlayer breathing and shear modes in few-trilayer MoS2 and WSe2.
abstract: Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently attracted tremendous interest as potential valleytronic and nanoelectronic materials, in addition to being well-known as excellent lubricants in the bulk. The interlayer van der Waals (vdW) coupling and low-frequency phonon modes and how they evolve with the number of layers are important for both the mechanical and the electrical properties of 2D TMDs. Here we uncover the ultralow frequency interlayer breathing and shear modes in few-layer MoS2 and WSe2, prototypical layered TMDs, using both Raman spectroscopy and first principles calculations. Remarkably, the frequencies of these modes can be perfectly described using a simple linear chain model with only nearest-neighbor interactions. We show that the derived in-plane (shear) and out-of-plane (breathing) force constants from experiment remain the same from two-layer 2D crystals to the bulk materials, suggesting that the nanoscale interlayer frictional characteristics of these excellent lubricants should be independent of the number of layers.
authors: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371.
authors: Yanyuan
authors: Y
authors: Zhao
authors: Xin
authors: X
authors: Luo
authors: Hai
authors: H
authors: Li
authors: Jun
authors: J
authors: Zhang
authors: Paulo T
authors: PT
authors: Araujo
authors: Chee Kwan
authors: CK
authors: Gan
authors: Jumiati
authors: J
authors: Wu
authors: Hua
authors: H
authors: Zhang
authors: Su Ying
authors: SY
authors: Quek
authors: Mildred S
authors: MS
authors: Dresselhaus
authors: Qihua
authors: Q
authors: Xiong