The band structure of Li2B4O7(100) and
Li2B4O7(110) was experimentally determined using a
combination of angle-resolved photoemission and angle-resolved inverse
photoemission spectroscopies. The experimental band gap depends on
crystallographic direction but exceeds 8.8 eV, while the bulk band gap is
believed to be in the vicinity of 9.8 eV, in qualitative agreement with
expectations. The occupied bulk band structure indicates relatively large
values for the hole mass; with the hole mass as significantly larger than
that of the electron mass derived from the unoccupied band structure. The
Li2B4O7(110) surface is characterized by a very light mass
image potential state and a surface state that falls within the band gap of
the projected bulk band structure.