Photoemission studies of interface effects on thin film properties
Ricci, Dominic A.
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https://hdl.handle.net/2142/35220
Description
Title
Photoemission studies of interface effects on thin film properties
Author(s)
Ricci, Dominic A.
Issue Date
2006-05
Doctoral Committee Chair(s)
Chiang, Tai-Chang
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Photoemission Spectroscopy
Surface Systems
Thin Films
Schottky Barrier Tuning
Thermal Stability Control
Language
en
Abstract
As the thickness of a metallic film decreases to the atomic scale, the confinement of the film's electrons by its boundaries gives rise to discrete electronic states, known as quantum well states, which dominate the film properties. This work investigates the use of film-substrate boundary modification as a means to control the film properties through the manipulation of its quantum well states. Specifically, the Schottky barrier heights and thermal stability temperatures for Pb(111) films grown on metal-reconstructed Si(111) substrates are shown to be determined by the interfacial conditions produced by the various Si-terminating metals (Au, Ag, In, and Pb), known as interfactants.
These properties are probed experimentally with angle-resolved photoemission spectroscopy using vacuum ultraviolet synchrotron radiation. An analysis of the measured quantum well energy levels and peak widths determines the height of the Schottky barrier, the rectifying energy barrier at a metal-semiconductor junction. A calculation based on the known interface chemistry and the electronegativity yields predicted barrier heights in good agreement with the experiment. These results demonstrate that the Schottky barrier height can be tuned to a desired value through an appropriate selection of interfactant.
Extending the exploration of interfactant effects to physical properties, the thermal stability temperatures of Pb films are measured with photoemission. The quantized electronic structure in Pb films causes the thermal stability to oscillate with an approximate bilayer period. A comparison among the systems reveals a phase reversal and an amplitude deviation in the stability temperatures. For Pb/In- 3 x 3 /Si(111), films made of odd numbers of atomic layers are observed to be more stable than the even ones, but this trend is reversed for the other cases studied. For Pb/Au-6x6/Si(111), the maximum stability temperatures are in excess of room temperature, unlike the other systems. These results show that the temperature-dependent thermal stability behaviors can be controlled by interfacial engineering.
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