Non-contact microsphere--surface adhesion measurement via acoustic base excitations

A non-contact adhesion measurement technique based on acoustic base excitation and laser interferometery has been introduced and demonstrated. The vibrational motion of 21.4-microm polystyrene latex particles (PSL) microspheres on surfaces were excited in the frequency range of 0-3.5 MHz, and their axial displacement responses were measured by an interferometer. It is shown that the rolling motion is dominant compared to the axial displacement of the bond. Using a formula for the rotational moment resistance of the particle-surface adhesion bond and the equation of rotational motion, the natural frequency of the rotational motion is related to the work of adhesion of the particle and substrate materials. The substrate materials used in the experiments include copper, aluminum, tantalum, and silicon. Measured work of adhesion values are compared to the data reported in the literature and good agreement is found.