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

Journal article


Publication Details

Author(s): Ostapenko A, Klöffel T, Meyer B, Witte G
Journal: Langmuir
Publication year: 2016
Volume: 32
Journal issue: 20
Pages range: 5029-5037
ISSN: 0743-7463
eISSN: 1520-5827


Abstract

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 Authors / FAU Editors

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


Additional Organisation
Exzellenz-Cluster Engineering of Advanced Materials


External institutions with authors

Philipps-Universität Marburg


Research Fields

A3 Multiscale Modeling and Simulation
Exzellenz-Cluster Engineering of Advanced Materials


How to cite

APA:
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. https://dx.doi.org/10.1021/acs.langmuir.6b00487

MLA:
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.

BibTeX: 

Last updated on 2019-16-03 at 16:10