Substrate-induced growth of organic thin films: from (sub-) monolayers to multilayers

Speaker:
Prof. Dr. Peter Zeppenfeld, Institute of Experimental Physics, Johannes Kepler University Linz, Austria

Highly ordered organic thin films with specific electronic or optical properties form the basis of many applications and devices, such as organic field effect transistors (OFETs) or light emitting diodes (OLEDs). This has stimulated fundamental research on how particular molecular structures with specific physical properties can be designed.

Here we will discuss how single-crystalline surfaces can serve as templates for the growth of epitaxial layers with well-defined molecular arrangements and orientations. I will concentrate on rod-shaped molecules like oligophenylenes or acenes deposited on pristine and oxygen covered metal surfaces, which were studied by a combination of conventional surface science tools (STM, LEED, PEEM) and surface optical spectroscopy (RDS, DRS). Already during the formation of the very first monolayer different phases and molecular configurations may form, depending on the substrate crystalline orientation, molecular coverage and growth conditions [1-3]. These monolayers act as templates for the growth of subsequently deposited layers. The latter can either replicate the existing monolayer structure but often undergo structural and/or orientational phase transitions above a certain critical thickness [4, 5]. We will illustrate how these configurational changes can lead to drastic modifications of the electronic or optical properties as a function of the film thickness.

[1] L.D. Sun, J. Gall, G. Weidlinger, C.Y. Liu, M. Denk, P. Zeppenfeld, Phys. Rev. Lett. 110, 106101 (2013)

[2] Th. Wagner, M. Györök, D. Huber, P. Zeppenfeld, E.D. Glowaki, J. Phys. Chem. C 118, 10911 (2014)

[3] A. Thomas, W. Malone, Th. Leoni, A. Ranguis, Z. Chen, O. Siri, A. Kara, P. Zeppenfeld,

C. Becker, J. Phys. Chem. C 122, 10828 (2018)

[4] L.D. Sun, S. Berkebile, G. Weidlinger, M. Denk, R. Denk, M. Hohage, G. Koller, F.P. Netzer, M.G. Ramsey,

P. Zeppenfeld, Phys. Chem. Chem. Phys. 14, 13651 (2012)

[5] A. Navarro-Quezada E. Ghanbari, Th. Wagner, P. Zeppenfeld, J. Phys. Chem. C 122, 12704 (2018)