Anisotropic nanofriction on MoS2 with different thicknesses

• Published in: Tribology international 2019-06, Vol.134, p.308-316
• Main Authors: Cao, Xing'an, Gan, Xuehui, Lang, Haojie, Yu, Kang, Ding, Shuyang, Peng, Yitian, Yi, Wangmin
• Format: Article
• Language: English
• Subjects: Anisotropy; Atomic force microscopy; Energy dissipations; Lubrication; Molybdenum disulfide; Nanoelectromechanical systems; Orientation effects; Periodic variations; Periodicity; Puckering effect; Thickness; Two dimensional materials; Two dimensional models
• ISSN: 0301-679X; 1879-2464
• DOI: 10.1016/j.triboint.2019.02.010

The nanofriction on molybdenum disulfide (MoS2) plays a crucial role in the long-term stability and reliability of micro- and nano-electromechanical systems (MEMS/NEMS). The anisotropic nanofriction force on MoS2 as a function of thickness was studied by a calibrated atomic force microscopy (AFM) in ambient air. The nanofriction force on MoS2 with a thickness of 45.23 nm presents a periodicity of 180° correlating to the same periodicity of the sawtooth-type lattice orientation. The two-dimensional Prandtl-Tomlinson model that the longer moving length along the armchair lattice orientation dissipated more energy with respect to zigzag lattice orientation was adopted in interpreting the anisotropic nanofriction on MoS2 with a thickness of 45.23 nm. The observed anisotropic nanofriction on MoS2 with a thickness of 4.18 nm was attributed to the combination of the lattice orientation and puckering effect. The anisotropic nanofriction on MoS2 with a thickness of 1.49 nm was mainly due to the puckering effect dominating the nanofriction. As the thickness of MoS2 increased, the magnitude of nanofriction decreased, and the anisotropy ratio of nanofriction increased. The structural anisotropy coupling with thickness play an important role in the anisotropic nanofriction on MoS2. This study could provide the clue for the design of MoS2 and other two-dimensional materials in lubrication applications. •The thickness-dependent nanofriction anisotropy of MoS2 at nanoscale was first reported.•The puckering effect coupled with lattice orientation was proposed for the anisotropic nanofriction on MoS2 with different thicknesses.•The two-dimensional Prandtl-Tomlinson model based on energy dissipation was adopted in interpreting the anisotropic nanofriction of thick MoS2 nanosheets.