  An in situ tip preparation procedure compatible with ultra-low temperature
and high magnetic field scanning tunneling microscopes is presented. This
procedure does not require additional preparation techniques such as thermal
annealing or ion milling. It relies on the local electric-field-induced
deposition of material from the tip onto the studied surface. Subsequently,
repeated indentations are performed onto the sputtered cluster to mechanically
anneal the tip apex and thus to ensure the stability of the tip. The efficiency
of this method is confirmed by comparing the topography and spectroscopy data
acquired with either unprepared or in situ prepared tips on epitaxial graphene
grown on Ru (0001). We demonstrate that the use of in situ prepared tips
increases the stability of the scanning tunneling images and the
reproducibility of the spectroscopic measurements.
