  We report a simple method for the fabrication of Niobium superconducting (SC)
tips for scanning tunnelling microscopy which allow atomic resolution. The
tips, formed in-situ by the mechanical breaking of a niobium wire, reveal a
clear SC gap of 1.5 meV and a critical temperature Tc=9.2+-0.3 K as deduced
from Superconductor Insulator Normal metal (NIS) and Superconductor Insulator
Superconductor (SIS) spectra. These match the values of bulk Nb samples. We
systematically find an enhanced value of the critical magnetic field in which
superconductivity in the tip is destroyed (around 1 T for some tips) up to five
times larger than the critical field of bulk Nb (0.21 T). Such enhancement is
attributed to a size effect at the tip apex
