Berlin 2005 – scientific programme
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O: Oberflächenphysik
O 42: Oberfl
ächenreaktionen II
O 42.1: Talk
Tuesday, March 8, 2005, 10:45–11:00, TU EB407
Chemically induced electronic excitations during scattering and Eley Rideal reaction of hydrogen on gold surfaces — •Beate Mildner1, Yanka Yeliazova1, Eckart Hasselbrink1, and Detlef Diesing2 — 1Institute of Physical and Theoretical Chemistry, University of Duisburg-Essen, Campus Essen — 2Institut für Schichten und Grenzflächen 3, Forschungszentrum Jülich
It is well known that highly exothermic reactions on metal surfaces can cause electron emission, if an electron is ejected with an energy exceeding the metal workfunction. Electrons with low excitation energy can be detected using thin film Schottky or tunnel diodes with barrier energies EB < Φmetal. At first, we studied the scattering of H-atoms at room temperature. On the gold surface of a Ta/Ta2O5/Au tunnel junction we observed a H-atom induced tunnel current at 0 V bias voltage. Exposure to H2 does not cause any detectable currents. When the sample temperature is lowered to 170 K (≈ desorption temperature of atomic hydrogen) the hydrogen induced tunnel current increases by a factor of 6. Moreover, the shape of the transient current caused by the adsoption of hydrogen from a pulsed atom beam changes from a simple square form to a shape with an initial overshoot followed by a slow decay. We assign the overshoot and the increase of the tunnel current to an Eley Rideal reaction (Hgas + Had → H2). Applying a bias voltage to the tunnel junction, we compared the energetic structure of the electronic excitation during ER reaction with the one from a scattering process. The bias dependence reveals that electrons with increased energy are produced during the ER-reaction .