原子力显微镜中液桥生成机理探讨

液桥是引起大气环境下原子力显微镜（AFM）图像失真的重要原因，同时也是大气环境下黏着力的主要成分.研究液桥对于成像机理和样品特性的理解有重要意义.提出了AFM液桥生成的物理机理，由3个不同的物理过程组成，即:挤出过程、毛细凝聚和液膜流动.这3种过程的特征平衡时间对认识液桥生成的动力学过程非常重要，挤出过程的平衡时间与接触方式有关，毛细凝聚的平衡时间在微秒量级，而液膜流动的平衡时间随液膜黏度不同变化较大.在此基础上分析了这3种形成机理在AFM不同的操作模式下对液桥体积、毛细力和耗散能的贡献.

Study of Growth Mechanisms for the Liquid Bridge in Atomic Force Microscopes

The liquid bridge is the main reason for image distortion of an atomic force microscope (AFM) in the atmospheric ambiance, meanwhile the capillary force resulting from the liquid bridge dominates the adhesion force in this condition. Investigation of the liquid bridge is of great importance to understand the imaging mechanisms and the sample properties. Herein, 3 different growth processes were presented and analyzed for the growth mechanisms of the liquid bridge in AFMs, including the squeezing process, the capillary condensation and the motion of thin liquid film. The characteristic equilibrium times of the 3 processes are of great importance to the understanding of the liquid bridge’s growth dynamics. The equilibrium time of the squeezing process depends on the contact mode, that of the capillary condensation is at the μs order of magnitude and that of the liquid film motion varies drastically with different viscosities of the liquid film. The contribution of the corresponding 3 growth mechanisms to liquid bridge volume, capillary force and energy dissipation was comaratively studied in different AFM operation modes.