Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 19: Semiconductor Substrates: Structure, Adsorption and Growth

O 19.5: Poster

Montag, 7. März 2016, 17:00–19:30, Poster A

Real-space investigation of the reaction channels of acetylene on Si(001) — Patrick Kirsten, •Christian Länger, and Michael Dürr — Institut für Angewandte Physik, Justus-Liebig-Universität Giessen, 35392 Giessen

Ethylene and acetylene adsorption on Si(001) are benchmark systems for the understanding of adsorbate reactions on semiconductor surfaces. In the case of ethylene, the [2+2] cycloaddition proceeds via a mobile precursor state; in the final state the ethylene molecule is adsorbed either on top of one dimer or bridging two neighbored dimers of one dimer row. Due to different conversion barriers from the precursor into the final state, the on-top configuration is favored by a factor of ten at room temperature [1]. Early experiments on acetylene adsorption also report a precursor-mediated reaction channel [2]. On the other hand, DFT calculations suggest the existence of a direct reaction pathway for C₂H₂ on Si(001) [3].

In order to resolve this contradiction, we performed STM measurements after adsorption of acetylene at different surface temperatures. The ratio of on-top to end-bridge configurations is found to depend on surface temperature. From the temperature dependence, a precursor-mediated reaction is concluded and the barrier difference for the two reaction channels is calculated.

[1] Mette, et al., Chem. Phys. Lett. 483, 209 (2009).

[2] Clemen, et al., Surf. Sci. 268, 205 (1992).

[3] Cho and Kleinmann, Phys. Rev. B 69, 075303 (2004).