Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)

O 14.42: Poster

Monday, March 27, 2006, 18:00–21:00, P2

Investigation of structural and vibronic properties of Tetracene phases on Ag(111) — •Serguei Soubatch, Ruslan Temirov, and Stefan Tautz — International University Bremen, Bremen, Germany

Recently, two ordered phases of Tetracene on Ag(111) surface have been registered with low energy electron diffraction [1]: The so-called α-phase forms upon deposition at room temperature (RT) and subsequent cooling, while β-phase appears upon cooling, if Tetracene molecules are deposited on the substrate kept at 230K. The β-phase transforms into α-phase upon annealing at RT and subsequent cooling.

Here we report on our microscopic and spectroscopic study of these phases and the process of phase transformation. Unit cells found for both the phases from scanning tunneling microscopy images agree with good accuracy to those of reported in [1]. An additional ordered transition phase as well as a disordered phase have been observed for annealed films of initial β-phase. The comparison of high resolution electron energy loss spectra with calculated vibrational modes of a free Tetracene molecule reveals, that the α-phase is composed of flat laying molecules, while the β-phase consists of tilted ones, in conformity with [1]. However, STM images suggest that the ordered β-phase forms on top of a disordered layer of molecules.

[1] A. Langner et al., Surf. Sci. 574 (2005) 153.