Electronic structure of lithium tetraborate Li2B4O7 crystals. Cluster calculations and x-ray photoelectron spectroscopy

The surface core level shift for lithium at the surface of lithium borate

“…From prior studies of the surface-to-bulk core level shift [1,2] The binding energies for the bulk Li 1s component ( À 56.570.4 eV) tend to be somewhat higher in value than reported previously for lithium tetraborate (Li 2 B 4 O 7 ) [9] at À 55.7 eV. Without adequate preparation of the stoichiometric clean surface, we have reason to believe that surface contributions (with a core level binding energy of À 53.770.5 eV) will dominate even the core level photoemission spectra.…”

“…Using the Fermi level as the reference for the observed binding energies of the occupied and unoccupied states of Li 2 B 4 O 7 (11 0), as done here, differs from the sometimes common practice of assigning binding energies with respect to the valence band maximum for lithium borate [18]. Prior studies of lithium tetraborate also have assigned their binding energies with respect to the chemical potential or Fermi level [9]. We chose the latter convention for this investigation for ease of comparison.…”

“…Application of the technique to alkalimetal-containing compounds, in particular dielectric compounds should yield very large surface-to-bulk core level binding energy shifts. Surface-to-bulk core level shifts have been observed for oxides [8], but with only a few examples that have incorporated the alkali metals, particularly lithium [9,10]. With alkali metals, the concept of multiple valence states cannot apply so that any observation of a surface-to-bulk core level shift would suggest the presence of a surface electronic structure far different from the bulk.…”

“…For oxides like the lithium borates, surface termination should lead to a very different oxygen coordination of the alkali metal, yet there are few, if any, reports of a surface-to-bulk core level shift for lithium in such oxide compounds [9] or even for the tungsten and molybdenum bronzes, the latter being quasi-one-dimensional materials based on lithium or alkali metal chains [10].…”

Low-temperature crystal structure, specific heat, and dielectric properties of lithium tetraborate Li2B4O7

“…Lithium tetraborate is a broadband dielectric with E g = 7.57 eV and a transmission range of 165-6000 nm, 11,12 where the boron-oxygen framework mainly contributes to the formation of levels in the upper region of the valence band. 13 Li 2 B 4 O 7 shows photoluminescence, when excited with hard quanta 12 and rather high radiation resistance ͑ap-proximately 40 GW/ cm 2 ͒. 4 According to Ref.…”