AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA8
Adsorption of N on Fe(100): Diffusion and Adatom-Adatom Interactions Studied with Scanning Tunneling Microscopy

Thursday, November 5, 1998, 4:20 pm, Room 308

Session: Surface Diffusion
Presenter: M.O. Pedersen, University of Aarhus, Denmark
Authors: M.O. Pedersen, University of Aarhus, Denmark
L. Österlund, University of Aarhus, Denmark
E. Laegsgaard, University of Aarhus, Denmark
I. Stensgaard, University of Aarhus, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
The dynamics and adsorbate-adsorbate interactions of N adatoms on a Fe(100) surface have been studied using variable temperature Scanning Tunneling Microscopy (STM). By recording a sequence of STM images as a film, we can track the individual N atoms at low coverage, and study their mobility. From these STM films, the diffusion constant of the N atoms can be derived, and by varying the sample temperature from 299 K to 323 K, a diffusion barrier of 0.92 eV ± 0.04 eV and a prefactor of D@sub 0@ = 2.4 10@super -3@ cm@super 2@/s are found. This value of the diffusion barrier is in good agreement with the diffusion barrier calculated using Density Functional Theory.@footnote 1@ From the STM images, the N adatom pair correlation function can also be deduced, from which an ensemble interaction potential can be found. Measuring the ensemble interaction potential at two different coverages (0.034 ML and 0.10 ML), allows us to quantify the entropic contributions and thus find the direct pair interaction potential between the N atoms. As expected, the nearest neighbour interaction is found to be strongly repulsive, whereas the next nearest neighbour interaction is attractive. From the STM images, the N atoms are found to adsorb in the four-fold hollow site, confirming previous LEED experiments. Due to the attractive interactions between the N adatoms, island nucleation is observed, even at sub-monolayer coverage. @FootnoteText@ @footnote 1@J.J. Mortensen, L.B. Hansen and J.K. Norskov, private communication