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For the purpose of studying the effect of the hydrophobicity of a probe tip on biomolecule imaging with an atomic force microscope (AFM), we examined the interaction forces between the substrate and the probe tip. Through the force-distance measurement by using a soft contact cantilever with 0.06-N/m spring constant, the Si (100) surface treated with a HF solution exhibited smaller snap-in and adhesion forces than the simply cleaned Si surface. The reduction of the adhesion force can be attributed to a reduction of the capillary force between the probe tip and the substrate. Singlestranded DNA molecules were prepared on a freshly cleaved mica surface and AFM imaging was performed with a Si probe tip before and after HF treatment of the tip. The HF-treated Si tip with a hydrophobic tip surface revealed a better line width as the interaction range got narrower.