Two-dimensional band structure of a Li layer: Li/Be(0001)

Angle-resolved photoemission and inverse photoemission have been used to measure the two-dimensional dispersion of the energy bands of a single dense layer of Li grown on Be(0001). These two techniques show excellent agreement for both the Fermi-level crossing and the effective mass of the Li valence band. This band is parabolic, with an effective mass (${\mathit{m}}^{\mathrm{*}}$/m) of 1.8, which is larger than that predicted for an isolated atomic layer. The large effective mass may be due to hybridization with the substrate bands. An avoided band crossing of the Li band and the Be surface state is observed.