  Superconducting (SC) tips for scanning tunneling microscopy (STM) can enhance
a wide range of surface science studies because they offer exquisite energy
resolution, allow the study of Josephson tunneling, or provide spatial contrast
based on the local interaction of the SC tip with the sample. The appeal of a
SC tip is also practical. An SC gap can be used to characterize and optimize
the noise of a low-temperature apparatus. Unlike typical samples, SC tips can
be made with less ordered materials, such as from SC polycrystalline wires or
by coating a normal metal tip with a superconductor. Those recipes either
require additional laboratory infrastructure or are carried out in ambient
conditions, leaving an oxidized tip behind. Here, we revisit the vacuum
cleaving of an Nb wire to prepare fully gapped tips in an accessible one-step
procedure. To show their utility, we measure the SC gap of Nb on Au(111) to
determine the base temperature of our microscope and to optimize its RF
filtering. The deliberate coating of the Nb tip with Au fully suppresses the SC
gap and we show how sputtering with Ar$^{+}$ ions can be used to gradually
recover the gap, promising tunability for tailored SC gaps sizes.

Superconductivity