Photoemission Studies of Thin Metallic Overlayer Systems
Shapiro, Alan Paul
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https://hdl.handle.net/2142/77404
Description
Title
Photoemission Studies of Thin Metallic Overlayer Systems
Author(s)
Shapiro, Alan Paul
Issue Date
1987
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
Angle-resolved photoemission spectroscopy was used to study Ag(111) monolayers on six different substrates: Ni(001), Ni(111), Cu(001), Cu(111), Au(111), and Si(111)-(7x7). The properties of surface states were also examined for several related systems: Cu(111) covered by various thicknesses of Ag, and a bare Cu(332) stepped surface. Monolayer overlayers that are incommensurate with the substrate Ag on Ni(001), Ni(111), and Cu(111) or commensurate with the substrate only over a large unit cell Ag on Cu(001) show electronic structures essentially independent of the substrate orientation and material, except for an overall shift in binding energy. The overlayer electronic structure is somewhat different for the Ag/Au(111) system, where there is a nearly perfect overlayer-substrate lattice match as well as substantial overlap in energy bands of like characters. In the Ag/Si system, partially disordered overlayer growth and a strongly corrugated substrate surface structure cause the overlayer features in the spectra to broaden substantially. For thicker Ag overlayers on Cu(111), the growth mode of the Ag was determined to be layer by layer despite the large mismatch between the two lattices. The Cu(111) surface state was observed to evolve monotonically for increasing Ag overlayer thickness to eventually become the Ag(111) surface state. The measured rate of shift of the surface state binding energy can be explained qualitatively in terms of the degree of localization of the surface-state wave functions. For the stepped Cu(332) surface, a feature believed to be an L-gap surface state is observed just below the Fermi edge in the photoemission spectra. The properties of this surface state are compared with known properties of the Cu(111) L-gap surface state.
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