Cu overlayers on oxygen and on carbon monoxide adsorbed on tungsten (110)

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Abstract
The existence of Cu overlayers on O/W(110) and CO/W(110) was investigated using thermal desorption, work function, UPS, XPS, and energy loss measurements. It was shown that these layers exist and have very different properties from O/Cu/W(110) and CO/Cu/W(110), respectively. The most striking fact is that the work function at Cu monolayer coverage (slightly higher in the case of CO/W(110), probably because of Cu second layer formation and gaps in the first Cu layer) is almost that of Cu1/W(110) regardless of the underlying adsorbate. HeI UPS spectra show a Cu d‐band structure even at Cu submonolayer coverages for Cu/O/W and for Cu1/CO/W(110). A loss peak at 4.64 eV was found for both systems [and for Cu8/W(110)] at θCu≥0.2 for O/W(110), and at θCu≥0.6 for CO/W(110). This is tentatively interpreted as a Cu interband transition. Unexpectedly small shifts in Cu2p3/2 and O1s binding energies were found under all conditions; the reasons for the virtual absence of shifts are not understood. The main conclusion of this work is that overlayers of Cu on top of other adsorbates show metallic properties even at submonolayer Cu coverages.