Self-propelling micro-disks

In this paper we introduce a simple and scalable method to produce micrometer sized 'Janus' disks whose rim is coated half with platinum/palladium and half with gold. The disks pinned upright to the air/liquid interface exhibit self-propulsion of similar to 100 mu m/s when submerged in H2O2 solution, due to the catalytic growth of oxygen bubbles at the disks upper (platinum/palladium-coated) rim. The disks exhibit two different travel trajectories, linear and rotary, depending on the bubble growth position, and are propelled via two different mechanisms, the bubble growth and the bubble burst. The displacement speed due to the bubble burst is three orders of magnitude larger than from the bubble growth process, whereas displacement distances are of similar order of magnitude for both processes.