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https://hdl.handle.net/2142/30652
Description
Title
Core excitons in amorphous magnesium alloys
Author(s)
Slowik, John Henry
Issue Date
1973-06
Doctoral Committee Chair(s)
Brown, F
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
core excitations
magnesium alloys
Language
en
Abstract
High resolution photoabsorption spectra were obtained in the range 40200 eV for Mg-Group V alloys. Sharp line structure was discovered for amorphous alloys of Mg-Bi and Mg-Sb near the photoabsorption threshold of the Mg 2p core level. These lines were strongest for compositions corresponding to the formation of intermetal1ic compounds in the crystalline solid, and are thought to be due to the formation of core excitons. Variation in the strength of the excitonic resonance is explained by a simple screening argument.
Variation in the line shape of the threshold is described by a critical exponent, and appears to be continuous between compositions having insulating conductivity and compositions approaching metallic conductivity. The exciton broadened asymmetrically toward higher energy, eventually assuming a shape similar to that observed in pure Mg metal. This supports the idea that the metallic LII III threshold is a remnant exciton singularity.
,
The exciton lines appeared in pairs in the absorption spectra, due to the spin-orbit splitting of the 2p initial state. The ratio of the strengths of the two lines did not correspond to the simple value expected from the statistical weights of the j = 1/2, 3/2 states involved. This effect is caused by electron-hole exchange interaction, which suggests a compact exciton wave function. Furthermore, for sufficiently long screening lengths the excitons sharpened enough to uncover additional structure, possibly due to higher order members of an exciton series. The fact that excitons were not observed in crystalline alloys of Mg-Bi is attributed to a change in conductivity and the nature of the critical exponent in the ordered phase.
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