The surface states of lithium tetraborate

Abstract

The different low index surface terminations of lithium tetraborate, Li2B4O7, are dominated by electronic states that fall within the band gap of the projection of the bulk states. As a pyroelectric material, lithium tetraborate, Li2B4O7, is a wide band gap dielectric, yet the (110) surface has a much smaller band gap because of occupied surface states that fall at binding energies between the valence band maximum and the Fermi level. The (100) surface is dominated, however, by unoccupied surface states that also fall in the gap between the conduction band minimum and the valence band maximum, but at binding energies just below the conduction band minimum. These very different types of surface states are consistent with the assignment of occupied surface states to states that are observed near the Fermi level in photoemission studies of Li2B4O7(110). The unoccupied surface states are also seen to be consistent with the inverse photoemission spectra of Li2B4O7(100). Clearly, the different surface terminations of lithium tetraborate yield very different types of surface electronic states.