The electronic structure of Li sub(2)B sub(4)O sub(7) (110) and Li sub(2)B sub(4)O sub(7)(100)

The band structure of Li sub(2)B sub(4)O sub(7)(100) and Li sub(2)B sub(4)O sub(7)(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 Li sub(2)B sub(4)O sub(7)(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.