AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM2
CO Adsorption on Mn Films on Cu(100)

Friday, October 29, 1999, 8:40 am, Room 607

Session: Adsorption on Metals and Silicon
Presenter: M. Grüne, Universität Bonn, Germany
Authors: M. Grüne, Universität Bonn, Germany
G. Boishin, Bulgarian Academy of Sciences, Bulgaria
R.-J. Linden, Universität Bonn, Germany
T. Pelster, Universität Bonn, Germany
J. Breitbach, Universität Bonn, Germany
A. Frey, Universität Bonn, Germany
C. Becker, Universität Bonn, Germany
K. Wandelt, Universität Bonn, Germany
Correspondent: Click to Email
The adsorption of carbon monoxide on Mn films on Cu(100) at 100 K was studied by means of UPS, HREELS, LEED, TDS, and work function change measurements. On the c(8x2) Mn monolayer, two stages of adsorption can be separated. The first type of molecularly adsorbed CO increases the work function by 0.9 eV. HREEL spectra resolve at least 4 different adsorption states, which cannot be separated by dosing or annealing. We assign these to side-on CO, step sites, and different kinds of bridge-bonded sites. The substrate superstructure remains intact in this low-coverage range. No adsorbate-induced LEED spots can be observed. Further CO adsorption beyond a critical exposure leads to a destruction of the Mn film order accompanied by a change of the CO-metal interaction as revealed by UPS and a decrease of the work function by 0.16 eV. In HREELS an additional CO state can be identified, presumably ontop-CO. At submonolayer Mn coverages, CO adsorbs simultaneously on both Cu and Mn patches. A thick polycrystalline Mn film exhibits molecular adsorption preferably in the side-on geometry. Annealing of CO-covered monolayer films leads to a restructuring of the surface around 220 K, subsequent dissociation of CO around 300 K, accompanied by desorption with a maximum at 350 K. It is not possible to re-establish the ordered film structure by annealing. At submonolayer Mn coverages, an additional desorption maximum at 420 K can be attributed to CO desorption from the Mn island edges. If the surface has not been saturated with CO, molecules change from Cu to Mn sites upon annealing to 160 K. Annealing a CO-covered thick polycrystalline Mn film leads to complete CO dissociation around 210 K.