Core-level spectroscopy of the Ni/W(1Â 1Â 0) interface: Correlation of W interfacial core-level shifts with first-layer Ni phases

We have measured W 4f7/2 core-level photoemission spectra from W(1 1 0) in the presence of Ni overlayers, from ∼0.2 to ∼3 monolayers. Interfacial core-level shifts associated with first-layer Ni phases have been identified: −230 ± 15 meV for the 1 × 1 pseudomorphic phase and −70 ± 7 meV for the 7 × 1 close-packed commensurate phase. At higher Ni coverages the interfacial core-level shift is −100 ± 10 meV. These shifts are analyzed using the partial-shift model of Nilsson et al. [Phys. Rev. B 38 (1988) 10357]; the analysis indicates that the difference in binding energies between the 1 × 1 and 7 × 1 phases has a large contribution from structural differences between the two phases.