AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA9
Metastable States of Nitrogen Atoms Adsorbed on Ru(0001)

Monday, October 25, 1999, 4:40 pm, Room 607

Session: Reactions on Metals
Presenter: L. Diekhöner, Odense University, Denmark
Authors: L. Diekhöner, Odense University, Denmark
H. Mortensen, Odense University, Denmark
A. Baurichter, Odense University, Denmark
A.C. Luntz, Odense University, Denmark
Correspondent: Click to Email
There has been a tremendous amount of work in recent years in the study of nitrogen interacting with ruthenium, in part because of its possible role as an alternative ammonia catalyst. There is still considerable disagreement as to the maximum coverage of adsorbed N allowed on Ru surfaces. We report here a novel way to produce high coverage states of nitrogen atoms adsorbed on Ru(0001) using an atomic N atom beam for dosing. Low doses produces the well known low coverage overlayers. At higher atom beam doses, we find sequential fillings of several previously unknown higher coverage states on the surface, ultimately forming a maximum coverage of 1 ML N/Ru atom. A large decrease in Ru-N bond strength with N coverage is apparent in our results and is in good agreement with recent density functional calculations. A combination of these calculations and our experiments indicates that the higher coverage states are in fact metastable relative to associative desorption, stabilized only by an increase in the barrier between the gas phase and the adsorbed state with coverage as well. Independent confirmation of the higher barriers for the high coverage states was also obtained via laser induced thermal desorption (LITD). In these experiments the kinetic energy distribution of the N@sub 2@ formed in associative desorption was measured by time of flight (TOF) techniques. We find N@sub 2@ desorbing with high translational energy distributions, much higher than seen in earlier desorption experiments from low coverages. Preliminary analysis indicates barriers that are at least in excess of 1.5 eV.