Band dispersions of Ag(111) monolayers on various substrates

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Abstract
This paper describes angle-resolved photoemission and high-energy electron diffraction studies of the growth and electronic properties of Ag monolayers prepared on Ni(111), Ni(001), Cu(111), Cu(001), Au(111), and Si(111)-(7×7). In all six systems, the Ag overlayer structure is very close to the hexagonal close-packed Ag(111) structure. Thus the effect of the substrate can be studied without the complication of major structural changes in the overlayer. The two-dimensional band dispersions for the Ag valence states have been determined along high-symmetry directions for these systems except Ag-Si(111). The Ag overlayers on Cu(111), Ni(001), and Ni(111) are incommensurate with the substrate structure, and the overlayer band dispersions are very similar despite the large differences in the electronic and atomic structures of the substrates. Ag on Cu(001) forms a c(10×2) overlayer, and the photoemission results are somewhat different. Ag on Au(111) forms a lattice-matched epitaxial overlayer, and its band dispersions have a very different appearance. These similarities and differences are explained in terms of the degree of commensuration of the substrate-overlayer interaction as a perturbation on the overlayer properties. The growth of Ag on Si(111)-(7×7) is not as well ordered as in the other systems. A severe broadening of the overlayer photoemission features is observed, preventing the determination of the band dispersions. Momentum broadening as well as random crystal potential variation within the overlayer are likely to be the cause of the broadening.