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@PHDTHESIS{Zheng:877846,
      author       = {Zheng, Fengshan},
      title        = {{H}igh spatial resolution and three-dimensional measurement
                      of charge density and electric field in nanoscale materials
                      using off-axis electron holography},
      volume       = {221},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2020-02470},
      isbn         = {978-3-95806-476-8},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {XIX, 182 S.},
      year         = {2020},
      note         = {RWTH Aachen, Diss., 2020},
      abstract     = {The ability to make local measurements of charge density in
                      nanoscale materials and devices is essential for
                      understanding many material properties. The charge density
                      can then be used to infer the electric field or
                      electrostatic potential within and around the specimen. This
                      information is important for scientists working on subjects
                      such as field electron emissionand atom probe tomography.
                      Off-axis electron holography is a powerful technique that
                      can be used to record the phase shift of a high-energy
                      electron wave travelling through an electron-transparent
                      specimenin a transmission electron microscope. Information
                      about the charge density within the specimen can be
                      retrieved from the measured phase with high spatial
                      resolution. In this thesis, charge density and electric
                      field measurements are performed, both in projection and in
                      three dimensions, with a primary focus on samples that have
                      a needle-shaped geometry. Three approaches are used: an
                      analytical model-dependent approach, a
                      model-independentapproach and an approach based on numerical
                      model-based iterative reconstruction. The model-based
                      iterative approach allows $\textit{a priori}$ information,
                      such as the shape of the object and the influence of charges
                      that are located outside the field of view, to be taken into
                      account. More importantly, it also allows for the
                      reconstruction of three-dimensional charge density
                      distributions from incomplete tomographic tilt of phase
                      images without the artefacts that would be present if
                      conventional tomographic reconstruction algorithms were
                      used. In this thesis, a W$_{5}$O$_{14}$ nanowire is
                      investigated experimentally in the presence of anapplied
                      electrical bias and the charge distribution along it is
                      evaluated. A carbon fibre needle-shaped specimen is then
                      studied, in order to demonstrate the capability of the
                      modelbased iterative approach to measure the
                      three-dimensional charge density, electric field and
                      electrostatic potential both inside and around it. Finally,
                      a systematic investigation of electron-beam-induced charging
                      in a needle-shaped specimen with an insulating
                      Al$_{2}$O$_{3}$ apex is presented, including the dependence
                      of the results on electron dose rate, total dose,
                      temperature, primary electron energy and the surface state
                      of the sample. Great care is required with the acquisition
                      and interpretation of the results, in particular because
                      charging phenomena are sensitive to the electrical
                      conductivity of the sample, the presence of contact
                      potentials and the presence of (unknown) surface states.},
      cin          = {ER-C-1 / PGI-5},
      cid          = {I:(DE-Juel1)ER-C-1-20170209 / I:(DE-Juel1)PGI-5-20110106},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/877846},
}