Formation and Stability of Phenylphosphonic Acid Monolayers on ZnO: Comparison of In Situ and Ex Situ SAM Preparation

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Details zur Publikation

Autor(en): Ostapenko A, Klöffel T, Meyer B, Witte G
Zeitschrift: Langmuir
Jahr der Veröffentlichung: 2016
Band: 32
Heftnummer: 20
Seitenbereich: 5029-5037
ISSN: 0743-7463
eISSN: 1520-5827


Self-assembled monolayers (SAMs) enable an electronic interface tailoring of conductive metal oxides and offer an alternative to common transparent electrodes in optoelectronic devices. Here, the influence of surface orientation and pretreatment on the formation and stability of SAMs has been studied for the case of phenylphosphonic acid (PPA) on ZnO single crystals. Using thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray adsorption fine structure spectroscopy (NEXAFS) and density-functional theory (DFT) calculations, the thermal stability and orientational ordering of PPA-SAMs on the polar and mixed-terminated ZnO surfaces were analyzed. On all surfaces, PPA-SAMs remain stable up to 550 K, while at higher temperatures a C--P bond cleavage and dissociative desorption takes place yielding two distinct desorption peaks. Based on DFT calculations, these desorption channels are attributed to protonated and deprotonated chemisorbed PPA molecules, which can be related to tri- and bidentate species, hence allowing to determine their relative abundance from the intensity ratio. Beside immersion, an alternative monolayer preparation based on vacuum deposition in combination with controlled desorption of excess multilayers is demonstrated. This enables a SAM preparation on bare ZnO surfaces without any precoating due to exposure to ambient air, which is further compared with SAM formation on intentionally hydroxylated substrates. Corresponding TDS data indicate that initial hydroxylation favors the formation of tridentate and deprotonated bidentate, while the OMBD preparation on bare surfaces yields a larger fraction of protonated bidentate species. The orientation of PPA molecules adopted in the SAMs was determined from the dichroism of K-edge NEXAFS measurements and reveals an almost upright orientation for the deprotonated species, while a slight tilting is obtained for monolayer films with a large fraction of protonated bidentate molecules.

FAU-Autoren / FAU-Herausgeber

Klöffel, Tobias
Interdisziplinäres Zentrum für Molekulare Materialien
Meyer, Bernd Prof. Dr.
Professur für Computational Chemistry

Zusätzliche Organisationseinheit(en)
Exzellenz-Cluster Engineering of Advanced Materials

Autor(en) der externen Einrichtung(en)
Philipps-Universität Marburg


Ostapenko, A., Klöffel, T., Meyer, B., & Witte, G. (2016). Formation and Stability of Phenylphosphonic Acid Monolayers on ZnO: Comparison of In Situ and Ex Situ SAM Preparation. Langmuir, 32(20), 5029-5037.

Ostapenko, Alexandra, et al. "Formation and Stability of Phenylphosphonic Acid Monolayers on ZnO: Comparison of In Situ and Ex Situ SAM Preparation." Langmuir 32.20 (2016): 5029-5037.


Zuletzt aktualisiert 2019-16-03 um 16:10