| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 88 === The effects of van der Waals and capacitive forces in atomic force microscopies are investigated in both smooth and rough surfaces. The parameters of rough surfaces are considered the sizes of grain and the distances between a sample and a microscopic tip. The geometry of microscopic tip are samplied as a cone type. The different angles of tip are also investigated. Numerical calculations can be provided and simulated the real forces between the tip-surfaces. By computational method , comparison of van der Waals and the capacitive forces in different measurement parameter are achieved.
In this paper, we have calculated the van der Waals forces and capacitive forces in smooth surface. The results show that the van der Waals forces is the dominant factor than the capacitive forces when the distance between the tip and sample is less than half-distance of radius of tip. We conclude that the electrostatic force is always dominant for a tip-surface larger than half of the tip radius of curvature. When the surface is uniform roughness, the capacitive force is larger van der Waals force that the distance between tip-sample is over several nanometers. The angle of tip discreased, the interaction between the tip-surface is increased. However the effect to change distance is main. This results are achieved to design the best profile of tips to measure the complicated samples.
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