Visualizing asymmetric Coulomb blockade in nanoislands on a semiconductor

Coulomb blockade (CB) in nanoscale systems arises when charging energy blocks electron tunneling at low voltages. Scanning tunneling microscopy (STM) enables precise control of tunneling junctions, yet how work function differences between tip, island, and substrate affect CB remains unclear. We use STM to study CB in indium nanoislands on black phosphorus. Differential conductance measurements show equally spaced Coulomb peaks from single-electron charging, with spatial variations due to capacitance changes. The peak dispersion axis is offset from zero bias and shows distinct asymmetry on either side. We show that work function mismatches cause this asymmetric behavior, which would otherwise be symmetric. Our findings demonstrate how junction properties control charge transport and enable improved single-electron manipulation.