Abstract
Thermal programmed desorption spectra for the CO/K/Ni(110) system are analyzed through Monte Carlo simulation. Results support a picture for the coadsorbate phase based on different sites for the adsorption of K (four-fold coordinated sites) and CO (on-top sites) with a direct, short ranged, attractive K-CO interaction whose intensity is estimated to be -0.25 eV.
| Original language | English |
|---|---|
| Pages (from-to) | L636-L639 |
| Journal | Surface Science |
| Volume | 275 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Sep 1 1992 |
Funding
of TPD spectrag iven in figs. 2b and 2c must be simultaneouslyfi tted. The first thing we found out from several attemptst o simulatet he desorptionp rocessw as that different adsorptions ites should exist for K and CO on the Nit1 10)s urface.I n fact, if this was not so, then a third peak at approximately7 00 K was alwaysp resent.T his third peak arises from configurationso f the kind K-CO-K (wherea CO has two NN K), due to a stronga ttractiveK -CO interaction necessary to generate the double-peakede xperimentasl pectra. To avoid this difficulty, dual lattices,w ith different sites for K and CO adsorption,s hould be considered. By looking at the unreconstructed Ni(ll0) surface,f ig. 4a, we propose a dual lattice like that of fig. 4b, where filled circles represent K adsorption sites, which are four-fold coordi-natedt o Ni atoms,a nd open circlesr epresentC O adsorption sites correspondingt o on-top positions with respectt o Ni atoms.T his choice is in coincidence with LCAO calculations for the coadsorptiono f CO and K on FeflOO) 1141H. ow-ever, due to the fact that K ionic diameter is about 2.66 A and the Ni-Ni nearest neighbor separation is 2.49 A, the maximump ossible K coveragea llowed by the model is 0.5, i.e., only every second site along [110] direction can be occupiedb y a K atom.D ue to the samea rgument CO must adsorbi n a tilted or perpendicularf orm on top of a Ni atom if it has an adsorbedK in a nearest-neighbopr osition. This possibilityi s supported by experimentale vidence through XPD