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@PHDTHESIS{Just:902558,
      author       = {Just, Sven},
      title        = {{D}isentangling parallel conduction channels by charge
                      transport measurements on surfaces with a multi-tip scanning
                      tunneling microscope},
      volume       = {69},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2021-04357},
      isbn         = {978-3-95806-574-1},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Information
                      / Information},
      pages        = {xii, 225 S.},
      year         = {2021},
      note         = {RWTH Aachen, Diss., 2021},
      abstract     = {Within this thesis, both position-dependent charge
                      transport measurements with a multi-tip scanning tunneling
                      microscope (STM) are performed, and theoretical models for
                      describing these measured data are developed. Only a
                      combination of both allows for actually disentangling
                      multiple current transport channels present in parallel, in
                      order to reveal the physical properties of the investigated
                      systems, i.e. the conductivity of the individual channels.
                      In chapter 2, the instrumental setup for the multi-tip STM
                      is shown in general and the specific methods used for tip
                      positioning are discussed. An introduction into the theory
                      of distance-dependent four-point resistance measurements is
                      given in chapter 3. Here, the relations between four-point
                      resistance and conductivity influenced by the chosen probe
                      geometry are discussed for both a pure two-dimensional and a
                      pure three-dimensional system. Furthermore, also anisotropic
                      conductance in two dimensions is considered. Chapters 4 –
                      7 depict actual measurements with the multi-tip STM on
                      different sample systems, as semiconductors and topological
                      insulators. First, in chapter 4 the conductivity of the
                      Si(111)-(7×7) surface and the influence of atomic steps of
                      the underlying substrate are investigated. In order to
                      interpret the measured resistances, a 3-layer model is
                      introduced which allows for a description by three parallel
                      conductance channels, i.e. the surface, the space charge
                      region and the bulk. Such a model enables to extract a value
                      for the surface conductivity from the measurements.
                      Moreover, by a measurement of the conductance anisotropy on
                      the surface, the conductivity of a single atomic step can be
                      disentangled from the conductivity of the step-free
                      terraces. In chapter 5, the 3-layer model is extended to an
                      N-layer model in order to model the strongly depth-dependent
                      conductivity of the near-surface space charge region in
                      semiconductors in a more precise way. In order to
                      demonstrate the universal applicability of the N-layer
                      model, it is used to extract values for the surface
                      conductivity of Ge(100)-(2×1) and Si(100)-(2×1)
                      reconstructions from data already published in the
                      literature, but not evaluated in terms of the surface
                      conductivity. Chapter 6 depicts a further combined
                      experimental and theoretical approach in order to reveal
                      parallel conductance channels in topological insulators thin
                      films, i.e. the interface channel at the boundary to the
                      substrate and the interior of the film itself, which are
                      both in parallel to the transport channel through the
                      topological surface states at top and bottom surface of the
                      film. From measurements on specific surface reconstructions,
                      the conductivity of the interface channel can be revealed,
                      while the interior of the thin film is approached by band
                      bending calculations in combination with results from
                      angle-resolved photoemission spectroscopy measurements
                      (ARPES). [...]},
      cin          = {PGI-3},
      cid          = {I:(DE-Juel1)PGI-3-20110106},
      pnm          = {5213 - Quantum Nanoscience (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5213},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/902558},
}