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@PHDTHESIS{Schmitz:845340,
      author       = {Schmitz, Christoph},
      title        = {{O}perando {X}-ray photoemission electronmicroscopy
                      ({XPEEM}) investigations of resistive switching
                      metal-insulator-metal devices},
      volume       = {53},
      school       = {Universität Duisburg},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-02614},
      isbn         = {978-3-95806-283-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Information
                      / Information},
      pages        = {IX, 153 S.},
      year         = {2018},
      note         = {Universität Duisburg, Diss., 2017},
      abstract     = {Resistive switching materials - including resistive oxides
                      - raise significant scientific and industrial interest due
                      to their potential applications in next generation
                      non-volatile data storage devices and as building blocks for
                      novel logic elements. Even though numerous resistive
                      switching materials already found their way into
                      application, the underlying physical mechanisms still remain
                      highly elusive. While the electronic response of these
                      systems is well-documented throughout literature,
                      experimental data on microscopic and chemical origin of
                      resistive switching is rare. Scope of the present work is to
                      gain a deeper physical understanding of chemical and
                      electronic changes taking place during the switching process
                      by means of chemically-sensitive and spatially resolving
                      X-ray photoelectron emission microscopy (XPEEM). This
                      technique is used to identify chemical and electronic
                      changes between the ON and OFF states of non-functional
                      delaminated memristive SrTiO$_{3}$ devices. For the low
                      resistive (ON) state, sub-micron filamentary regions are
                      observed showing significant contributions of trivalent Ti,
                      whereas the high resistive (OFF) statelacks these states and
                      structures. The experimentally derived chemical and spatial
                      fingerprints provide evidence for oxygen vacancy
                      accumulation respectively depletion being predicted by the
                      valence change model. Further analysis of the observed
                      filament substructure indicates that the observed
                      macroscopic filaments consist of an inhomogeneous matrix of
                      nanoscale islands. These findings contribute to the
                      fundamental understanding of the switching mechanism being
                      essential to improve device simulations and to identify
                      scaling limits. Beyond the conventional static
                      characterization of the ON and OFF states of non-functional
                      devices, the focus of the thesis is to evaluate how the
                      highly surface-sensitive PEEM approach can be improved to
                      allow monitoring the anticipated chemical changes also
                      during operation of a device (’operando’). In this
                      context different experimental approaches and device
                      geometries are discussed and evaluated, which have the
                      potential to circumvent the top electrode surface
                      sensitivity dilemma in photoemission-based techniques.
                      Ultra-thin graphene top electrodes are demonstrated to be
                      sufficiently transparent for electrons and thus allow to
                      image chemical signals originating from the buried active
                      interface of a metal-insulator-metal structure by means of
                      X-ray absorption spectroscopy. The novel strategies and
                      concepts are realized into a set of functional devices.
                      Additional technical modifications are implemented into a
                      PEEM instrument operated at a synchrotron facility. Using
                      this new setup chemical and electronic characterization of a
                      working device are simultaneously performed in a single
                      experiment providing a direct correlation between
                      current-voltage (I-V) response and chemical state for the
                      first time. Results from the operando and in-situ
                      experiments are obtained from single devices and thus
                      exclude typically observed device-to-device variations and
                      experimental artifacts typically hampering the analysis. The
                      instrumental advances and improved methods documented in
                      this thesis enable operando characterization of functional
                      devices using PEEM. They are not limited to resistive
                      switching and they present a significant step towards the
                      long-termgoal of visualizing the switching dynamics on a
                      nanosecond timescale with sub-micron spatial resolution.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      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/845340},
}