Teflon cylinder and mounted onto a stage consisting of a clamp and micromanipulator. Next, the C-UME was manually brought down with the micromanipulator onto a rotating disk polisher, the surface of which was covered with lapping film. The lapping film was kept wet during polishing by dropwise addition of Millipore water. Precision polishing of the tip electrode consisted of several steps. For each polishing step, the tip was contacted with the polishing film for 5 to 10 s.