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Photon‐induced field desorption of NO from Rh
Author(s) -
Drachsel W.,
Teutsch Th.
Publication year - 2007
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.2469
Subject(s) - fluence , desorption , ionization , field desorption , atomic physics , ion , chemistry , irradiation , photon energy , electric field , photon , crystal (programming language) , analytical chemistry (journal) , laser , adsorption , optics , physics , programming language , organic chemistry , quantum mechanics , chromatography , computer science , nuclear physics
The effect of an electric field on the NO photo‐desorption from Rh was investigated using a pulsed laser atom probe. Experiments were carried out at 78 K by irradiating a [111] oriented Rh field‐emitter tip and a Rh single crystal of 1.4 mm diameter at 6.4 eV and at 3.2 eV photon energy. The energies and masses of the emitted ions were evaluated from time‐of‐flight (ToF) measurements. For 6.4 eV irradiation of the Rh tip, a quadratic yield dependence on the laser fluence has been observed for NO. This is interpreted as a two‐photon ionization of field‐adsorbed NO; this is supported by the same behavior of O 2 and Xe but at a comparatively lower yield. In cases where the ionization energy of the probed species (Ar, N 2 , CO) is higher than 12.8 eV no such effect is observed. Laser irradiation with 2.3 eV photons initiates thermally assisted field desorption of the species at a comparatively higher fluence. Ion energy analysis suggests re‐neutralization of NO + in the forbidden zone, but the translational energy gained appears to be sufficient to overcome the desorption barrier and field ionizion at the critical distance becomes probable. At low laser fluence a weak linear photo‐desorption process has been detected, presumably caused by substrate‐mediated electronic excitation as a first step. In this model, the photo‐desorbed NO will subsequently be field‐ionized, and accelerated away by the field. For the Rh single crystal, NO photo‐desorption, with two‐photon ionization in a second step, is deduced as the most probable mechanism. Copyright © 2007 John Wiley & Sons, Ltd.