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@PHDTHESIS{Creutzburg:441043,
      author       = {Creutzburg, Marcus},
      othercontributors = {Stierle, Andreas},
      title        = {{A}dsorption of {C}arboxylic {A}cids on {M}agnetite
                      {S}ingle {C}rystal {S}urfaces},
      school       = {Universität Hamburg},
      type         = {Dissertation},
      address      = {Hamburg},
      publisher    = {Verlag Deutsches Elektronen-Synchrotron},
      reportid     = {PUBDB-2020-02286, DESY-THESIS-2020-011},
      series       = {DESY-THESIS},
      pages        = {160},
      year         = {2020},
      note         = {Dissertation, Universität Hamburg, 2020},
      abstract     = {Magnetite is a versatile transition metal oxide with
                      applications in catalysis, biomedical imaging and spintronic
                      devices. Moreover, magnetite nanoparticles covered with
                      oleic acid are formed into novel nanocomposite, hierarchical
                      materials with outstanding mechanical properties in terms of
                      strength and hardness. Despite their strong influence on the
                      stability and properties of the nanocomposites, little is
                      known about interactions that take place at the
                      oxide/organic interface. In order to further tailor and
                      improve these materials, it is necessary to study the
                      controlled adsorption of carboxylic acids on well-defined
                      flat magnetite single crystal surfaces.Following the surface
                      science approach the clean magnetite (111) surface was
                      investigated in this thesis using low energy electron
                      diffraction (LEED), scanning tunneling microscopy (STM) and
                      surface X-ray diffraction (SXRD). The surface was found to
                      be Fe-tet1 terminated after several cycles of argon ion
                      sputtering and annealing in an oxygen atmosphere followed by
                      annealing in ultra-high vacuum (UHV). The surface was
                      homogeneously terminated by a Fe-tet1 layer however, the
                      surface defect concentration, i.e. missing tet1 ironions,
                      was around $35\%.The$ clean magnetite (111) surface was
                      subsequently exposed to formic acid. As the simplest
                      carboxylic acid, formic acid has been used as a probe
                      molecule for longer carbonchain carboxylic acids in the
                      past. The molecule was found to dissociate upon adsorption
                      at room temperature. Fourier transform infrared
                      reflection-absorption spectroscopy (FT-IRRAS)revealed two
                      adsorption sites for the formate molecule. For low
                      coverages, the formate molecule was adsorbed at the surface
                      in a chelating bidentate geometry with both formate oxygen
                      atoms bound to a single substrate tetrahedral iron ion and
                      the remaining atomic hydrogen was bound to the oxygen
                      terminated iron defect sites. With increasing coverage,
                      formic acid was adsorbed in a quasi-bidentate configuration
                      with one formate oxygen bound to a tetrahedral iron ion and
                      the other bound to an OH group on the surface. The surface
                      was covered by a (sqrt(3) x sqrt(3)) R30° superstructure at
                      saturation coverage, which was visible with LEED and STM.
                      Both adsorption geometries contributed to the formation of
                      the superstructure.The adsorption of oleic acid on the
                      magnetite (001) surface at room temperature was observed to
                      lift $90\%$ of the (sqrt(2) x sqrt(2)) R45° reconstruction
                      of the clean surface as proven by LEED and SXRD. The lifting
                      mechanism is expected to follow the same path as for the
                      adsorption of atomic hydrogen, water vapor and formic acid
                      on magnetite (001). The adsorption of hydrogen destabilizes
                      the tetrahedral interstitial iron, which subsequently
                      diffuses into one of the two octahedral vacancies. The
                      second vacancy is filled by iron diffusion from deeper
                      layers. FT-IRRAS results revealed that oleic acid molecules
                      adsorbed in a bidentate bridging geometry and the long
                      carbon chain was oriented perpendicular to the surface. With
                      increasing oleic acid coverage, non-dissociated molecules
                      started to adsorb parallel to the surface.The adsorption of
                      oleic acid on the magnetite (111) surface was different from
                      the (001) surface. Both dissociated and non-dissociated
                      molecules were adsorbed in an upright geometryresulting in a
                      higher layer thickness and higher electron density than on
                      the (001) surface as determined by X-ray reflectivity (XRR).
                      When annealing the oleic acid layer at 350 °C, the
                      thickness and electron density of the layer decrease on both
                      magnetite (111) and on (001) as a result of molecule
                      desorption and possible tilt. In addition an atomic
                      roughening of the magnetite substrate occurs.The different
                      adsorption behavior of formic and oleic acid on the (001)
                      and (111) magnetite single crystal surfaces and the
                      subsequent structural changes in the near-surface region of
                      magnetite are important aspects for oleic acid stabilized
                      magnetite nanoparticles. The structural properties of such
                      nanocomposite materials can be tailored by changing the
                      ratio of (111)-type and (001)-type facets hence changing the
                      oleic acid molecule density.},
      cin          = {FS-NL},
      cid          = {I:(DE-H253)FS-NL-20120731},
      pnm          = {6214 - Nanoscience and Materials for Information Technology
                      (POF3-621) / SFB 986 A07 - Adsorption organischer Säuren
                      auf Oxidoberflächen und Nanostrukturen (A07) (318017425) /
                      DFG project 192346071 - SFB 986: Maßgeschneiderte
                      Multiskalige Materialsysteme - M3 (192346071) / PHGS,
                      VH-GS-500 - PIER Helmholtz Graduate School
                      $(2015_IFV-VH-GS-500)$},
      pid          = {G:(DE-HGF)POF3-6214 / G:(GEPRIS)318017425 /
                      G:(GEPRIS)192346071 / $G:(DE-HGF)2015_IFV-VH-GS-500$},
      experiment   = {EXP:(DE-H253)Nanolab-02-20150101 /
                      EXP:(DE-H253)Nanolab-01-20150101 /
                      EXP:(DE-H253)Nanolab-03-20150101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      doi          = {10.3204/PUBDB-2020-02286},
      url          = {https://bib-pubdb1.desy.de/record/441043},
}