Quantum well states ofsp- andd-character in thin Au overlayers on W(110)

Photoemission spectra are reported for Au on W(110) which show series of pronounced peaks up to large film thicknesses [about 15 monolayer (ML)] which are assigned to quantum-well states of Au sp and Au d character. Due to its large $5d$ bandwidth and low binding energy, sp and d states are largely degenerate in Au. Therefore, Au overlayers serve as an interesting test system for simple models of quantum-well-state formation. A good description of all of the observed features is reached based on our extended phase accumulation model analysis. Assignment to several branches of sp- and d-type quantum-well states is reached based on (i) our model treatment, (ii) the asymptotic behavior for large thicknesses, (iii) an analysis of the angle dispersion, and (iv) a comparison between the system without and with an extra Ag interlayer. For the latter it is found that sp-type quantum-well states form throughout the combined (Au+Ag) layer already from lowest coverages on, whereas formation of d-type quantum-well states is largely suppressed. Using our model treatment we reach a thorough description of both systems for the whole thickness range starting out from submonolayer coverages and correct previous assignments in the literature. In addition, the role of sp-d hybridization in the overlayer is discussed.