Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 14: Oxide Surfaces: Adsorption and Reactivity

O 14.8: Talk

Monday, March 16, 2015, 16:45–17:00, MA 042

Surface etching of single crystalline ZnO by phosphonic acid based SAMs — •Alexandra Ostapenko and Gregor Witte — Molekulare Festkörperphysik, Philipps-Universität Marburg, Renthof 7, 35032 Marburg, Germany

Self-assembled monolayers (SAMs) attachment have proven to be an effective way of tuning electronic interfacial properties or specifically link dye-molecules to transparent metal oxides. Organic-inorganic hybrid systems based on the latter approach have recently attracted significant research interest because of their promising use in photovoltaic application. The resulting device performance is expected to depend critically on the microstructure of the film. Widely used phosphonic acid based SAMs form surprisingly robust films on ZnO surfaces. However, it was found that during the film deposition phosphonic acid anchoring causes surface damaging resulting from dissolution-precipitation of ZnO. For the extended immersion times we observe the formation of star shaped surface defects of crystalline needles on single crystalline ZnO substrates. We show that the etching rate can be tuned directly by variations of pH-value during the immersion. Structure and composition of surface precipitations and their thermal stability were investigated combining atomic force spectroscopy, X-ray diffraction spectroscopy and thermal desorption spectroscopy. Preparative routes to optimize film formation avoiding surface etching were elucidated as well.