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

Abstract

Petrosky, J. C.; McClory, J.; Burak, Ya. V.; Adamiv, V. T.; and Dowben, Peter A., "The surface core level shift for lithium at the surface of lithium borate" (2009 Keywords:Oxide dielectric layers Lithium tetraborate Surface-to-bulk core level shift a b s t r a c t The shallow Li 1s core level exhibits a surface-to-bulk core level shift for the stoichiometric Li 2 B 4 O 7 (11 0) surface. Angle-resolved photoemission spectroscopy was used to indentify Li 1s bulk and surface core level components at binding energies À 56.5 7 0.4 and À 53.7 7 0.5 eV, respectively. We find photoemission evidence for surface states of Li 2 B 4 O 7 (11 0) that exist in the gap of the projected bulk density of states. The existence of surface states is consistent with the large surface-to-bulk core level shift for the Li 1s core.

The Electronic Structure and Secondary Pyroelectric Properties of Lithium Tetraborate

“…The temperature dependent angle-resolved photoemission spectra were obtained using linearly polarized synchrotron light dispersed by a 3m toroidal grating monochromator [7,17,18,70,71], at the Center for Advanced Microstructures and Devices (CAMD) [72]. The measurements were made in an ultra-high vacuum (UHV) chamber employing a hemispherical electron analyzer with an angular acceptance of ± 1°, as described elsewhere [70,71].…”

“…In other words, the dispersion of the valence bands should be small compared to the expected dispersion of the conduction bands. Only recently [5,7] has there has been experimental confirmation of any of the key predictions of the calculated band structure, beyond the band gap [5,7,16,17,18] and some of the optical properties [15]. …”

“…The sample temperature for these measurements was 623 ± 5 K, to reduce surface charging. Adapted from [7,17]. …”

“…After corrections for photovoltaic charging (as discussed later ( vide infra ) and elsewhere [5,7,16,17,18]), we place the Li 1s shallow core level binding energies at −56.7 ± 0.4 to −56.5 ± 0.4 eV depending on the surface termination (crystal orientation). These values are largely dominated by the bulk Li 1s core level binding energy contributions because of the normal photoelectron emission geometry.…”

“…The photovoltage charging, shown in Figure 8 and plotted in Figure 9, regrettably cannot be directly compared with the pyroelectric measurements (Figure 7), as illumination is required and such surface photovoltage measurements would tend to work best for a lithium borate surface that is largely defect free [43]. Measurements of the surface charging were essential in any case [5,7,17,18], as the electronic structure measurements reported in the prior section require suppression of surface charging to be a valid measure of electronic structure [7]. We note, in passing, that this is the reason why most of the electronic structure measurements reported in section 2 were done at 623 K, where surface photovoltage charging was found to be negligible [18] and the Li 2 B 4 O 7 (110) and Li 2 B 4 O 7 (100) surface exhibited a density of states that qualitatively resembles that expected from the model bulk band structure of Li 2 B 4 O 7 [5,7,17,18], as seen in Figure 1.…”