Adhesive force of the microstructures measured by the atomic force microscope

A technique for measuring the work of adhesion of microstructures using the atomic force microscope (AFM) is proposed. The adhesive force acting between a sharp probe and a sample is obtained from the deflection of a micromachined cantilever, which is measured precisely by heterodyne interferometry with a sensitivity of 20 pN. The adhesive force was investigated using an Si₃N₄ probe with a tip radius of 50 nm for an SiO₂ substrate and five kinds of solution: H₂O, C₂H₅OH, CH₃COCH₃, CCl₄, and KOH. The measured forces range from 10 to 100 nN. The force measured for CH₃COCH₃ is the smallest. This is consistent with the finding that the rise with CH₃COCH₃ reduces the pinning influence of the surface-micromachined structures. The effect of the surface roughness and the contact area on the adhesive force is examined, and the results are discussed in terms of macroscopic adhesive theory