Quantum Size Effects in Thin Films - Stability, Work Function, Superconductivity, and Pseudogap Structure

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Date/Time:Monday, 22 Feb 2010 from 4:10 pm to 5:10 pm
Location:Physics, room 5
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Tai C. Chiang (University of Illinois at Urbana-Champaign)

During epitaxial growth and thermal processing of metal thin films on semiconductors, the system often self-organizes into domains or islands of preferred heights. This extra stability for specific thicknesses or heights has an electronic origin; confinement of the electrons in the film causes the formation of quantum-well states, which cross the Fermi level periodically as the film thickness increases. These periodic Fermi level crossings give rise to one-dimensional shell effects, akin to the shell effects associated with the periodic table. As a result, large variations in film properties are expected and observed, including the surface energy that determines the stability and preferred heights, the work function and other surface properties, and the superconducting gap and transition temperature. This talk will present highlights in recent advances on this subject, including angle-resolved photoemission measurements of the electronic structure and experimental and theoretical determinations of the amplitude, phase, period, and damping of the property variations. The effects of phonon scattering, including a recently discovered pseudogap feature in thin Pb islands, will be discussed.