Interplay of crystalline strain and electronic properties in topological insulators and semiconductor thin films grown by Molecular Beam Epitaxy
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Universidade Federal de Minas Gerais
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Tese de doutorado
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Relação entre o strain cristalino e propriedades eletrônicas em filmes finos de isolantes topológicos e semicondutores crescidos por Epitaxia de Feixes Moleculares
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Membros da banca
Myriano Henriques de Oliveira Junior
Ricardo Wagner Nunes
Beatriz Diaz Moreno
Matheus Josué de Souza Matos
Ricardo Wagner Nunes
Beatriz Diaz Moreno
Matheus Josué de Souza Matos
Resumo
In this thesis, we studied three different types of samples, all obtained by the molecular
beam epitaxy technique (MBE). In the first set of samples, epitaxial layers of Silicon-Germanium (SiGe) after the Germanium condensation process were studied. Our results
show that, starting from a low concentration Si0.92Ge0.08 layer grown on top of a crystalline Si
(001) on SOI substrates, we can reach desirable Ge concentration with a non-monotonic
interplay on in-plane and out-of-plane strain. The Ge concentration and SiGe layer thickness
was evaluated by a combination of secondary ion mass spectroscopy (SIMS) and synchotron
X-ray measurements (diffraction and reflectivity).
In the second set of samples, we have studied the first stages of the heteroepitaxial growth
of layered bismuth telluride (Bi2Te3) topological insulator on top of highly oriented pyrolitic
graphite (HOPG). Samples were investigated by atomic force microscopy (AFM), synchrotron
x-ray diffraction (XRD), and micro-Raman spectroscopy. AFM images show
hexagonal/triangular flat islands with exposed HOPG areas for the low coverage regime. The
existence of pseudomorphic strain at the initial Bi2Te3 layers was retrieved by both XRD and
Raman spectroscopy.
Finally, in the third set of samples, we studied the morphological and electronic properties
of Bi2Te3 layers doped with Europium (Eu) atoms. Bi2Te3 layers were deposited on a Barium
fluoride (BaF2) substrate and characterized by atomic force microscopy (AFM) and scanning
tunneling microscopy/spectroscopy (STM/STS) techniques. Our results indicate regions along
the sample surface in which the signature of the topological surface states disappears as
well as the existence of a second crystalline phase.
Abstract
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Raios X, difração, Epitaxia por feixe molecular, Semicondutores
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Synchrotron x-ray diffraction, Atomic force microscopy, Scanning tunneling microscopy/spectroscopy, Ge condensation, Bismuth telluride, Topological insulators
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