Fourth-layer surface core-level shift on Be(0001)

Three surface shifted Be 1s components were identified in an earlier investigation of Be(0001). The theoretical results indicated, however, that also the fourth atomic layer may exhibit a shift large enough to make it separable from the bulk component. A photoemission investigation was therefore made and the results indeed show the presence of a fourth surface shifted component. Due to the size of the shift and the number and widths of the components involved the fourth-layer contribution does not appear as a resolved peak in recorded spectra. Utilizing curve fits of recorded and difference spectra the presence of a fourth shifted component is clearly demonstrated by the present data. Surface core-level shifts of -870 +/- 25, -605 +/- 25, -335 +/- 25, and -160 +/- 50 meV are extracted for layers 1-4. A refit of the old data assuming four surface components yielded shifts in agreement with the present values and fits of better quality, i.e., having smaller residuals.