横向应力场对原子尺度摩擦的调制

Modulation of Transverse Stress Field on Atomic-scale Friction

目的探索横向应力场对原子尺度摩擦能量耗散的调制规律。方法采用微机械剥离方法制备单层至多层MoS2样品,利用光学显微镜、高波数拉曼光谱、低波数拉曼光谱精确确定MoS2的层数。通过原子力显微镜,对单层至多层MoS2进行原子尺度摩擦实验,探索横向应力场对原子尺度摩擦参数及摩擦能量耗散的调制规律。基于独立振子模型,分别评价等效刚度k和表面势垒U0对MoS2原子尺度摩擦行为的影响,并通过独立振子模型计算MoS2原子尺度摩擦能量耗散。结果在无应变的情况下,随着MoS2层数的增加,等效刚度从2.92 N/m增加至7.41 N/m,表面势垒从0.36 eV增加至0.58 eV。单层MoS2平均摩擦力最大,双层MoS2次之,多层MoS2最小。当应变从0增加至1.06%时,单层MoS2的等效刚度从2.92 N/m增加到12.03 N/m,表面势垒从0.36 eV增加至2.94 eV,但是应力场对表面势垒的调制作用更强,从而导致相对势垒η与应力场呈正相关。随着应力场的增加,原子尺度摩擦能量耗散增加,而且当应力场刚开始作用于MoS2时,摩擦能量耗散显著增大。单层MoS2的摩擦能量耗散从无应变时的1.3×10^-13 J增加到应变为0.53%时的1.9×10^-12 J。结论研究能量耗散不仅有助于探究摩擦本质,而且可实现能量耗散的调制。该工作促进了原子尺度摩擦能量耗散的研究,为摩擦能量耗散调制提供了新的方向。

To explore the modulation of transverse strain field on friction energy dissipation in atomic scale,in this paper,monolayer to multilayer ultrathin MoS2 specimens were prepared by the mechanical cleavage technique.The layer number of MoS2 was identified with optical microscope,low-frequency Raman and high-frequency Raman.The atomic scale fraction experiments were carried out on monolayer to multilayer MoS2 to explore modulation of lateral stress field on the atomic dimension fraction parameters and fraction energy dissipation.Based on the independent oscillator model,the influences of two important parameters i.e.effective stiffness and surface potential barrier on the atomic-scale friction were investigated and the friction energy dissipation of MoS2 in atomic scale was calculated.Under no strain,when the layer number of MoS2 increased from monolayer to multilayer,the effective stiffness and surface potential barrier increased from 2.92 N/m to 7.41 N/m and from 0.36 eV to 2.94 eV,respectively.The average frictional force of monolayer MoS2 was the largest,that of bilayer MoS2 was the second,and that of multilayer MoS2 was the smallest.When the strain increased from 0 to 10.6%,the effective stiffness and surface potential barrier of monolayer MoS2 increased from 2.92 N/m to 12.03 N/m and from 0.36 eV to 2.94 eV,respectively.However,the effect of strain field on surface potential barrier modulation was stronger,which leaded to a positive correlation between the relative barrier and the strain.With the increase of the strain field,the friction energy dissipation at atomic scale increased;and when the stress field first acted on MoS2,there was a significant increase in the friction energy dissipation.The friction energy dissipation of monolayer MoS2 increased from 1.3×10^-13 J without strain to 1.9×10^-12 J with strain of 0.53%.Studying friction energy dissipation not only helps to explore the origin of friction,but also can realize the modulation of frictional energy dissipation.This work can promote the study of atomic-scale energy dissipation and provide a new direction for the modulation of frictional energy dissipation.