FLOW CELL FOR REAL-TIME OBSERVATION OF SINGLE-PARTICLE ADHESION AND DETACHMENT

A flow cell was built for observing particle removal from test surface s in real time. The removal force is the hydrodynamic force exerted on the particle by liquid flowing parallel to the lest surface. Particle removal was detected visually either through a microscope or on a vid eo monitor. All experimental results reported here are based on the re moval of deposited 10 mum polystyrene (PSL) spheres from one of 3 surf aces: polished aluminum; polished bare silicon wafers (native oxide on ly); or thermally oxidized silicon wafers. One of 3 cleaning liquids w as used: dilute SC-1, dilute SC-2, or de-ionized water containing 0.01 % Micro(R). The hydrodynamic removal force was controlled primarily by controlling the liquid flow rate. In all experiments, as the flow rat e increased, single polystyrene latex (PSL) spheres detached first, th en doublets, then triplets and finally larger agglomerates; that is, t he adhesion force increased more rapidly with agglomeration than the h ydrodynamic removal force. By applying theoretical calculations from t he literature, this flow cell can be used to estimate the hydrodynamic forces necessary for removal of particles from surfaces.