Stark-shifted image potential states of benzene bilayers on Cu(1Â 1Â 0) and Cu(1Â 1Â 1)

Comparison of constant-current z(V) spectra measured on the benzene monolayer on Cu(1 1 0) with spectra measured under the same conditions on the benzene bilayer on Cu(1 1 0). The n = 1 image state is seen to be shifted away from the Fermi level (V = 0) in bilayer regions when compared to monolayer regions.