THESIS
2019
xxii, 196 pages : illustrations (some color) ; 30 cm
Abstract
A large variety of two-dimensional (2D) materials exhibit unique physical and
chemical properties. Detailed knowledge of the structure and dynamical properties
of these intriguing modern materials is essential for developing a fundamental
understanding of their properties. In this thesis, investigations of the structure,
morphology, and dynamics of 2D materials on metal substrates have been carried
using low energy electron microscopy (LEEM) and diffraction (LEED). The
interplay of complementary anisotropic strain relief by nano-wrinkles and substrate-induced
corrugation in graphene on a vicinal copper surface is found to induce one
dimensional nano-wrinkle morphology perpendicular to facets/steps on the
underlying substrate. The residual compressive strain is determined using...[
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A large variety of two-dimensional (2D) materials exhibit unique physical and
chemical properties. Detailed knowledge of the structure and dynamical properties
of these intriguing modern materials is essential for developing a fundamental
understanding of their properties. In this thesis, investigations of the structure,
morphology, and dynamics of 2D materials on metal substrates have been carried
using low energy electron microscopy (LEEM) and diffraction (LEED). The
interplay of complementary anisotropic strain relief by nano-wrinkles and substrate-induced
corrugation in graphene on a vicinal copper surface is found to induce one
dimensional nano-wrinkle morphology perpendicular to facets/steps on the
underlying substrate. The residual compressive strain is determined using high
spatially-resolved μLEED measurements to be 0.7% and 0.3% perpendicular to
nano-wrinkles and facets, respectively. The substrate facets that induce corrugation
in graphene are identified using LEED facet spot analysis to be (110), (531), (351) and (665). This behavior contrasts with random wrinkle network that was observed
in the absence of substrate-induced corrugation on a singular copper surface. We
also observed the formation of a new oxygen-deficient 2D copper oxide structure at
the Cu(111) surface that exhibits intriguing domain pattern formation and dynamical
behavior. This structure may be attributed to a honeycomb-like Cu
2O(111) surface
oxide layer with a periodic array of Stone–Wales defects. Depletion of oxygen by
thermal desorption is accommodated by the formation of oxygen-free regions that
coexist with the oxide structure in a sequence of island, stripe and inverse island
patterns with decreasing oxygen content. Several sequential evolution mechanisms
of the characteristic length scale are identified by rescaling analysis of the structure
function that is measured from observations of phase separation during cooling.
Further development of LEEM image formation theory was also performed to
support extension of the work described in this thesis in the future. The extended
Fourier Optics (FO) approach for modeling image formation in aberration-corrected
LEEM is presented. This work broadens our capabilities to understand the origins of
LEEM image contrast and to perform quantitative evaluation of contrast.
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