Experimental band structure of ordered Cu overlayers on Ag(001)

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Abstract
We present an extensive systematic study of the electronic structure and epitaxial growth of ordered Cu films on clean Ag(001) surfaces. Angle-resolved photoemission with synchrotron radiation was used to map the two-dimensional band dispersions of monolayers and multilayers of Cu using several photon energies. Band symmetries were determined from polarization selection rules. At room temperature we observe pseudomorphic growth of Cu films for film thicknesses up to three atomic layers. Although our epitaxial results are very similar to those reported recently, we find a Cu 3d-band width more than twice as large. This discrepancy is attributed to their failure to observe the lowest Cu 3d bands. These bands are difficult to observe since they overlap intense Ag 4d emission at many photon energies. The use of polarized synchrotron radiation allowed us to measure the energy of the true d-band minimum. The Cu 3d-band width (3.15 eV) is virtually identical to that of bulk Cu, but the band center is about 0.25 eV lower. The band topology agrees well with calculations for supported and unsupported Cu monolayers, but theory tends to underestimate the 3d-band width.