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@PHDTHESIS{Jalil:909854,
      author       = {Jalil, Abdur Rehman},
      title        = {{E}ngineering topological superlattices and their epitaxial
                      integration in selectively grown hybrid nanostructures via
                      {MBE}},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      publisher    = {RWTH Aachen University},
      reportid     = {FZJ-2022-03467},
      pages        = {309},
      year         = {2022},
      note         = {Dissertation, RWTH Aachen, 2022},
      abstract     = {The realization of advanced spintronics applications
                      including the topological quantum computation, spin
                      manipulation for data storage, dissipation less ballistic
                      transport for ultra-fast quantum devices and topological
                      switching for low energy memory applications etc. became
                      more feasible with the experimental discovery of 3D
                      topological insulators (TIs). The incorporation of exotic
                      spin-momentum locked Dirac surface states (of 3D TIs) into
                      these futuristic complex quantum devices requires not only
                      the growth of high crystal quality epilayers but also the
                      fabrication of pristine nanostructures, topological band
                      engineering, ultra-smooth and defect-free surfaces, and
                      atomically transparent epitaxial interfaces. This work deals
                      with a systematic study of epitaxial growth of convention 3D
                      TIs via molecular beam epitaxy(MBE) and atomic-scale
                      structural characterization via scanning transmission
                      electron microscope (STEM)to explore the above mentioned
                      requirements. At first, the relation between the growth
                      parameters and the defect density in the Van-der-Waals (VdW)
                      based layered structures is investigated. The optimum growth
                      parameters are extracted and the defect-free epilayers are
                      prepared. Later, the technique of selective area epitaxy
                      (SAE) is explored to develop a platform to achieve a
                      scalable nano-architecture. Utilizing CMOS compatible
                      fabrication technology, Si (111) substrates with crystalline
                      and amorphous combinational surfaces are prepared. The
                      precisely controlled growth parameters facilitated the
                      realization of selectively grown topological structure.
                      Based on statistical analysis, a generalized growth model is
                      established that provided control over structural defects
                      through the effective growth rate at the nanoscale and
                      assisted in achieving high quality nanostructures. Based on
                      conventional 3D TIs, the capabilities of VdW epitaxy are
                      exploited further with the growth of topological-trivial
                      hetero structures. The stoichiometric adjustment in these
                      hetero structures is utilized as a tool to control the
                      strength of spin-orbit coupling (SOC) and to engineer the
                      topological band structure. Two such systems are explored
                      including BixTey = (Bi2)m(Bi2Te3)n and GST/GBT =
                      (GeTe)n(Sb2Te3/Bi2Te3)m. With the continuous addition of Bi2
                      bilayers and GeTe (materials that exhibit trivial phase)
                      into 3D TIs, the stoichiometric modulations are achieved.
                      Moreover, the modification of growth parameters is conducted
                      to incorporate these stoichiometries with the pre-patterned
                      substrates and selectively grown nanostructures of the
                      corresponding alloys are prepared. Assisted by the
                      atomic-scale structural characterizations, the phenomenon of
                      VdW reconfiguration is explored to observe the
                      transformation of layer architecture; the key mechanism in
                      the evolution of interfacial phase change materials
                      (IPCMs).Moreover, the systematic alterations in the atomic
                      interaction and resulting changes in bond lengths within a
                      pristine and hybrid VdW stacks are investigated. The focus
                      is then shifted towards surfaces where the stability
                      (inertness) of TI epilayers in the ambient conditions via
                      structural and compositional investigations, is analyzed. An
                      undeniable evidence of the aging effect in all material
                      systems is obtained where a non-saturating oxidation process
                      at the (0001) surfaces with a continually decreasing
                      oxidation rate is witnessed. Using the in situ thin film
                      deposition of Al (2 nm),the top surfaces are passivated and
                      the aging effect is neutralized. The phenomenon of charge
                      transfer due to band alignment at the Si (111) - TI bottom
                      surface is investigated with a comparative growth,
                      structural and transport analysis of TI epilayer prepared on
                      HfO2 substrate. Finally, the interfaces between TIs and
                      various s-wave superconductors (SCs) are explored. The
                      challenges to achieve the induced superconductivity in TI-SC
                      hybrid junction and highly transparent interfaces are
                      addressed. The issue of metal diffusion into the TI epilayer
                      and the resulting formation of Schottky-like barriers is
                      avoided with the introduction of a thin metallic film as a
                      diffusion barrier. Using the natural tendency of transition
                      metals to transform into their corresponding
                      di-chalcogenides (TMDCs) at the exposure to TI surfaces,
                      atomically well-defined and VdW assisted epitaxial
                      interfaces are engineered. The newly evolved interfaces
                      assisted in achieving the induced superconductivity that was
                      a huge limitation in realizing the complex functional
                      devices.},
      cin          = {PGI-9},
      cid          = {I:(DE-Juel1)PGI-9-20110106},
      pnm          = {5221 - Advanced Solid-State Qubits and Qubit Systems
                      (POF4-522)},
      pid          = {G:(DE-HGF)POF4-5221},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2022-06227},
      url          = {https://juser.fz-juelich.de/record/909854},
}