Evidence of a rolling motion of a microparticle on a silicon wafer in a liquid environment
The interaction of micro- and nanometer-sized particles with surfaces plays a crucial role when small-scale structures are built in a bottom-up approach or structured surfaces are cleaned in the semiconductor industry. For a reliable quantification of the interaction between individual particles and a specific surface, however, the motion type of the particle must be known. We developed an approach to unambiguously distinguish between sliding and rolling particles. To this end, fluorescent particles were partially bleached in a confocal laser scanning microscope to tailor an optical inhomogeneity, which allowed for the identification of the characteristic motion pattern. For the manipulation, the water flow generated by a fast moving cantilever-tip of an atomic force microscope enabled the contactless pushing of the particle. We thus experimentally evidenced a rolling motion of a micrometer-sized particle directly with a fluorescence microscope. A similar approach could help to discriminate between rolling and sliding particles in liquid flows of microfluidic systems.