Neutron and x-ray scattering studies of layered solids
Neumann, Dan Alan
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https://hdl.handle.net/2142/25457
Description
Title
Neutron and x-ray scattering studies of layered solids
Author(s)
Neumann, Dan Alan
Issue Date
1987
Doctoral Committee Chair(s)
Zabel, Hartmut
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
neutron scattering
x-ray scattering
layered solids
graphite intercalation compounds
molecular beam epitaxy
Language
en
Abstract
We report inelastic and quasielastic neutron scattering
studies of graphite intercalation compounds and x-ray scattering
studies of semiconductor films and superlattices which were
grown by molecular beam epitaxy. For graphite intercalation
compounds, these include measurements of the [00 1]
longitudinal phonons in the ternary compounds K 1_xRbxCB and
KC24 (ND3)x. The results for the K-Rb compound show an
anomalous softening of the compressional elastic constant c33.
This stage 1 system also displays one optic mode behavior
which can be described by a simple virtual crystal model. No
local or gap modes were observed. The acoustic branch of the
stage 1 K -ammonia ternary shows a splitting due to coupling of
these phonons to a dispersionless librational excitation of the
ammonia molecules. In addition, the interlayer force constants
in this compound are appreciably softer than in its binary
counterpart. We then go on to describe quasielastic neutron
scattering results for a hydrogenated K-ammonia sample, which
show the existence of two separate molecular rotations and also
translational diffusion of the ammonia. The final study of
graphite intercalation compounds shows that the Lyddane-SachsTeJler
(LSTI splitting for excitations polarized in the [001]
direction is quenched by free carrier screening in the stage 1
binary CsC8.
The x-ray scattering results involve two types of systems:
GaAs grown on Si and Ge substrates and terraced superlattices.
First, we show that the polar semicondoctor GaAs can be grown
free from antiphase domains on non-polar Si and Ge substrates.
This is done by carefully measuring the widths of various Bragg
peaks and showing that the broadening can be completely
described in terms of residual strain and finite crystallite size.
We then conclude by describing the phenomena of terracing for
both unstrained and strained-layer superlattices. A model is
presented which reasonably accounts for the peak positions,
widths, and intensities for the strained-layer system
GaAs/GaAs1 -xS b x.
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