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      Understanding scanning tunneling microscopy contrast mechanisms on metal oxides: a case study

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      Author
      Mönig, H.
      Todorović, M.
      Baykara, M. Z.
      Schwendemann, T. C.
      Rodrigo, L.
      Altman, E. I.
      Pérez, R.
      Schwarz, U. D.
      Date
      2013
      Source Title
      ACS Nano
      Print ISSN
      1936-0851
      Publisher
      American Chemical Society
      Volume
      7
      Issue
      11
      Pages
      10233 - 10244
      Language
      English
      Type
      Article
      Item Usage Stats
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      133
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      Abstract
      A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2√2×√2)R45 missing row reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip-sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip-sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip-sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip-sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters. © 2013 American Chemical Society.
      Keywords
      STM contrast
      DFT simulation
      Metal oxide
      Tip asymmetry
      Tip chemistry
      Tip oxidation
      Permalink
      http://hdl.handle.net/11693/20710
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/nn4045358
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      • Department of Mechanical Engineering 272
      • Institute of Materials Science and Nanotechnology (UNAM) 1831
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