Surface thermomigration of nanoscale Pt-Si droplets on stepped Si(100)

The motion of Pt-Si liquid nanodroplets and their interaction with atomic steps on Si(100) has been studied using low-energy electron microscopy. Submicron droplets migrate across the surface in the direction of the lateral temperature gradient as demonstrated by overlain maps of migration velocity and sample temperature. The thermal migration motion is opposed by a drag force normal to substrate steps, which strongly deflects smaller droplets to move parallel to step edges but hardly affects larger ones. In addition, steps are dragged along by moving droplets before eventually depinning. The resulting curved steps can create "roadways" that collect droplets and guide their motion, resulting in a non-Ostwald coarsening process involving guided collision and coalescence.