Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 31: Surface Chemical Reactions and Heterogeneous Catalysis I

O 31.6: Vortrag

Dienstag, 27. März 2007, 17:00–17:15, H38

Electronic energy dissipation of deuterium and hydrogen atoms on gold and platinum surfaces — Beate Mildner, Eckart Hasselbrink, and •Detlef Diesing — Fachbereich Chemie and Centre for Nanointegration (CeNIDE), Universität Duisburg-Essen, D-45117 Essen, Germany

Chemical surface reaction as adsorption and Langmuir Hinshelwood (LH) reaction may dissipate their excess energy to substrate and adsorbate vibrations or to electronic degrees of freedom. The latter ones can only be detected externally by light emission or when the dissipated energy exceeds the electronic work function Φ of the metal. Electronic surface excitations E< Φ can be monitored on the surface of thin film tunnel devices. We use tantalum–tantalum oxide–top metal tunnel junctions. As top metal 5 nm thick Pt films or 12 nm thick Au films were used. Both enable a ballistic transport of excited electrons (holes) with excess energies up to 1 eV from the surface to the oxide interface. The excited carriers are then detected in the tantalum backelectrode as a tunnel current. Bunches of H and D atoms (5·10¹⁵ atoms in 20 seconds) were emitted to the top metal. On Au surfaces the tunnel current trace can be assigned predominantly to LH reactions. H atoms cause a 4.5 times higher tunnel signal than D atoms. On Pt surfaces the tunnel current trace is dominated by the adsorption process which is reasonable due the higher binding energy. On Pt surfaces the tunnel current signals of hydrogen and deuterium are comparable. The results are compared to recent DFT calculations.