Robust, carbon related, superconducting nanostructure at the apex of a tungsten STM tip

By pulsing the tunneling voltage between the Tungsten (W) tip of a Scanning Tunneling Microscope (STM) and a graphene-covered metal surface, a superconducting (SC) nanostructure is formed at the apex of the STM tip. We have characterized the SC properties of the resulting nanotip as a function of temperature and magnetic field, obtaining a transition temperature of 3.3 K and a critical field well above 3 T. The SC nanotip is robust and stable and achieves atomic resolution. A non-SC tip can be easily recovered by controlled voltage pulsing on a clean metal surface. The present result should be taken into account when studying zero-bias features like Kondo resonances, zero-bias-conductance peaks, or superconductivity on graphene-based systems by means of STM using tungsten tips.