Photoemission studies of noble metal semiconductor systems
The study of the structural and electronic properties of semiconductor surfaces and of thin metallic films deposited upon them is a topic of fundamental and practical interest. Clean and Au and Ag covered surfaces of Ge(lll)-c(Zx8), Si(lll)-(7x7), Ge(lOO)-(Zxl), and Si(lOO)-(Zxl) are studied in this work with high-resolution core-level, valence-band, and angle-resolved photoemission, and high-energy electron diffraction (HEED). In conjunction with the results of other surface studies, notably of scanning tunneling microscopy (STM), the findings reveal significant details of, and correlations between, these systems' structural and electronic properties. Dispersive bulk-derived transitions are observed with angleresolved photoemission and mapped along high-symmetry directions in the Brillouin zone for most of the clean substrates. The previous surfacestate assignments are rigorously confirmed. Quantitative structural details for these surfaces are deduced with the aid of core-level line shape analysis. The results agree with recent STM topographs. Valence-band density-of-states spectra show the familiar bulk and surface-derived features. A study is made of the initial stages of Au and Ag adsorption upon these surfaces. Overlayer growth morphologies are investigated with HEED. The deposition of noble-metal atoms induces significant modifications of surface structural and electronic properties. The results establish correlations between the electronic and structural properties of the substrate surfaces and have implications for possible growth models of Au and Ag upon them. This experimental approach is of general utility and adoptable for studies of other systems. The thin-film overlayers are studied in detail. A novel labeling technique unambiguously shows that less than 0.1 monolayer (ML) Ge segregates on top of thin films of Ag on Ge(ll1). Angle-resolved photoemission studies are performed for Ag(111) films 0-17 ML thick on Si(111). The Ag(l11) L-gap surface-state precursor is evident in films as thin as 2 ML. Bulk-like, dispersive Ag-4d band transitions are observed and mapped along the [111] direction of the Brillouin zone. Ag sp-band thin-film states are probed and their associated quantum defects measured.
photoemission studies, nobel metal semi-conductor systems, thin metallic films
University of Illinois - Urbana-Champaign
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