Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers

Rumpel A, Novak M, Walter J, Braunschweig B, Halik M, Peukert W (2011)

Publication Language: English

Publication Type: Journal article, Original article

Publication year: 2011

Journal

Book Volume: 27

Pages Range: 15016 - 15023

Volume: 27

Issue: 24

Journal Issue: 24

URI: http://pubs.acs.org/doi/abs/10.1021/la203916h?prevSearch=%255BAllField%253A%2B%255BAllField%253A%2BTuning%2Bthe%2BMolecular%2BOrder%2Bof%2BC60%2BFunctionalized%2BPhosphonic%2BAcid%2BMonolayers%255D%255D&searchHistoryKey=

DOI: 10.1021/la203916h

Abstract

Mixed self-assembled monolayers (SAM) of alkyl phosphonic acids and C60 functionalized octadecyl phosphonic acids (C60C18–PA) are deposited on alumina substrates from solution and are shown to form wellordered structures with an insulating layer of alkyl chains and a semiconducting layer that comprises mainly C60. Such an ordered structure is a necessity for the application of SAMs in organic transistors but is difficult to obtain since C60C18–PA without additional support do self-assemble in dense packaging but not in a well-ordered fashion. To avoid disordering of the SAM and to gain a better control of the interfacial properties we have investigated the stabilizing effects of fluorinated dodecyl phosphonic acids (FC12–PA) on the C60C18–PA monolayer. Vibrational sum-frequency (SFG) spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and electrical measurements were applied to study the mixed monolayers. Here, we make use of the differently labeled PA to determine surface coverages and molecular properties of the two species independently. Adsorption of FC12–PA gives rise to vibrational bands at 1344 cm-1 and 1376 cm-1 in SFG spectra, while a pronounced vibrational band centered at 1465 cm-1 is attributable to C60 vibrations. The coexistence of the bands is indicative for the presence of a mixed monolayer that is composed of both molecular species. Furthermore, a pronounced maximum in SFG intensity of the C60 band is observed for SAMs, which are deposited from solutions with  75\% C60C18–PA and  25\% FC12–PA. The intensity maximum originates from successful stabilization of C60 modified C60C18–PA by FC12–PA and a significantly improved molecular order. Conclusions from SFG spectra are corroborated by electric measurements that show best performance at these concentrations. Our results provide new information on the morphology and composition of C60 modified SAMs and establish a route to fabricate well-defined layers for molecular scale organic electronics.

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APA:

Rumpel, A., Novak, M., Walter, J., Braunschweig, B., Halik, M., & Peukert, W. (2011). Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers. Langmuir, 27(24), 15016 - 15023. https://doi.org/10.1021/la203916h

MLA:

Rumpel, Armin, et al. "Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers." Langmuir 27.24 (2011): 15016 - 15023.

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