VUV emission from the heavy alkali metals and rare gas impurities in alkali metals
First, Phillip Neal
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https://hdl.handle.net/2142/23902
Description
Title
VUV emission from the heavy alkali metals and rare gas impurities in alkali metals
Author(s)
First, Phillip Neal
Issue Date
1988
Doctoral Committee Chair(s)
Flynn, C.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
VUV emission
heavy alkali metals
rare gas impurities
excitation spectrum
core-level spectroscopies
Language
en
Abstract
Core excitations in metals create a local change in potential that couples strongly to the sea of conduction electrons. The response of the electron liquid to this local shock is reflected in its excitation spectrum; this can be probed by various core-level spectroscopies. The research described in this thesis investigates emission spectra from outer-core excitations using two model experimental systems that should be free of complicated band structure.
Emission from the np5( n +1)82 -T np6( n +1)8 outer core transitions in the heavy alkali metals K (n = 3), Rb (n = 4), and Cs (n = 5) has been examined as a function of temperature. The results are analyzed in terms of simple models to explain lineshape similarities and to extract lifetime and phonon broadening contributions. Samples were prepared by evaporation under ultra-high vacuum conditions and studied using electron beam excitation for temperatures from 15 K to 300 K. Phonon effects are found to conform well to established theories, and the lifetimes so determined for this important series of metals show clear systematics. Energetics of an emission feature associated with atoms on the free metal surfaces are also described adequately by current theories. These are the only experiments to date concerning emission from Rb or Cs.
Rare gas impurities in alkali metal host lattices, when studied previously by
absorption metods, showed an anomalously broad and suppressed Fermi edge, in
contrast to theoretical predictions. It was speculated that this threshold shape may
be characteristic of conduction electron recoil from the shock of the local optical
event. Analogous np5(n +1)8 --t np6 transitions in emission for Kr (n = 4) and Xe (n = 5) impurities in the alkali metals have been obtained in the present work. These show a broad lineshape near threshold, but different from that found for absorption. The observed small overlap between emission and absorption spectra firmly establishes that the bulk of the broadening seen in absorption is indeed characteristic of the electronic excitation spectrum. The form of the emission spectrum has focussed attention on local configurational effects as a possible explanation of the absorption, rather than the shake-up caused by electronic recoil.
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