| A liquid film resulting from the absorption of vapor may appear on a sample surface and will significantly distort the measurements made by atomic force microscope(AFM). This problem involves a coupled fluid-solid interaction. Although there have been many studies on the deformation of a semi-infinite liquid induced by the AFM probe tip, physical understanding of liquid film and its effects are still greatly needed for practical measurement. In order to elaborate the liquid film effect, we need to know how the liquid film deforms under its interaction with AFM probe tip.Due to the flowability of liquid, the film will no longer remain flat under its interaction with the tip. By employing force balance to the deformation of liquid film under its interaction with AFM tip and substrate, we established the equation governing the deformation of liquid film and obtained the expression of the apex height of the liquid bump. Through an improved model, the governing equation is also obtained by energy minimization. When AFM tip reaches a critical distance to the liquid surface, the liquid surface will jump up to contact the probe. Since this critical phenomenon characterizes the interaction among tip, liquid film and solid substrate, in this thesis, we present the critical condition for the liquid film to jump up to the tip. Furthermore, we discussed the order of the critical apex height, and find that it remains the same as that of a semi-infinite liquid, governed by a combination of tip radius, liquid surface tension and Hamaker constants of liquid.Strictly speaking, the value of critical bump apex height is dependent on film thickness and Hamaker constant difference between sample and liquid. The variation of the critical bump apex height with film thickness shows three distinct regimes for the case with various Hamaker constant difference.Above all, the study provides a physical understanding of what a liquid film is under AFM and its effects on the interaction between AFM tip and sample.
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