  Motivated by the discovery of superconductivity in the infinite-layer
nickelate family, we report an experimental endeavor to clean the surface of
nickelate superconductor Pr0.8Sr0.2NiO2 films by Ar+ ion sputtering and
subsequent annealing, and we study their electronic structures by cryogenic
scanning tunneling microscopy and spectroscopy. The annealed surfaces are
characterized by nano-sized clusters and Coulomb staircases with periodicity
inversely proportional to the projected area of the nanoclusters, consistent
with a double-barrier tunneling junction model. Moreover, the dynamical Coulomb
blockade effects are observed and result in well-defined energy gaps around the
Fermi level, which correlate closely with the specific configuration of the
junctions. These Coulomb blockade-related phenomena provide an alternative
plausible cause of the observed gap structure that should be considered in the
spectroscopic understanding of nickelate superconductors with the
nano-clustered surface.
