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.