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Title:Angle-resolved photoemission studies of quantum-electronic coherence in metallic thin-film systems
Author(s):Brinkley, Matthew K.
Director of Research:Chiang, Tai-Chang
Doctoral Committee Chair(s):Budakian, Raffi
Doctoral Committee Member(s):Chiang, Tai-Chang; Stone, Michael; Pitts, Kevin T.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):angle-resolved photoemission
electronic structures
quantum-well states
thin films
Abstract:When the thickness of a film approaches the nanoscale, the confinement of electrons in the film by its surface and interface gives rise to distinct electronic states known as quantum-well states. Related to the electromagnetic standing waves in an optical Fabry-Perot interferometer, electrons in a quantum well undergo mirror-like reflections at the film surface and substrate-film interface. At thicknesses comprising only a few monolayers N, the discretization of the electronic structure creates a dependency proportional to 1/N on the electronic properties of the film. In addition to providing a unique academic setting for the exploration of quantum mechanics under finely tuned conditions, ultrathin-film systems offer a glimpse into issues with which the electronic-device industry will have to contend in the near future. This thesis describes two experiments. The first of these concerns an angle-resolved photoemission study of the electronic structure of Pb films prepared on atomically uniform Ag(111) films. The data host a striking Fabry-Perot-like structure typical of a high-finesse Pb/Ag/Si(111) interferometer. Remarkably, the quantized electronic structure of the Ag films persists despite Pb overlayers much thicker than the photoemission escape depth and an incommensurate Ag/Pb interface. The simulations presented quantify the coherent coupling of the Ag and Pb electronic structures, affording a useful and non-invasive means for accessing deeply buried structures. This demonstrated exploitation of electronic coherence will prove useful to applications requiring the characterization of multilayer structures. The second experiment presents an ostensible quantum-number catastrophe in Ag films on Si(111) substrates. Angle-resolved photoemission studies of the quantum-well electronic structure in atomically uniform Ag films on Si(111)-(7x7) reveal an anomalous bifurcation of one of the subbands as it disperses toward the Fermi level. This bifurcation creates an apparent quantum-number paradox, as subbands must be associated with consecutive integer quantum numbers. The bifurcation migrates upon annealing from subband to subband toward the zone center and ultimately vanishes. Various tests indicate that this puzzling behavior arises from transverse resonances in the film electronic structure caused by the reconstruction at the interface. These resonances likely manifest in many thin-film systems involving incommensurate interfaces and/or interfacial reconstructions modulating the film structure. This work provides insight regarding the impact of film morphology and buried interfacial structures on the overall electronic structure of the system.
Issue Date:2010-08-31
Rights Information:Copyright 2010 by Matthew Kendrick Brinkley. All rights reserved.
Date Available in IDEALS:2010-08-31
Date Deposited:2010-08

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