Emergence of surface states in nanoscale Cu₂N islands

We studied electronic states in nanoscale Cu₂N islands on Cu(100) using scanning tunneling microscopy and density functional theory. Tunneling spectra indicate a state at ∼2 V in large islands (>20 nm2), which shifts due to quantum confinement in smaller islands. This state is not observed for islands with fewer than ∼50 atoms. In contrast, a 4 V state persists down to 12 atom islands, but it does not shift within experimental error. Theory suggests that these differences reflect the different effective masses of the two Cu₂N bands, as well as their coupling to a Cu surface state.