J. of Phys. Chem. B106, 8161 (2002)
F. E. Olsson(1), M. Persson(1), N. Lorente(2),,L.
J. Lauhon(3), and W. Ho(4)
(1)Department of Applied Physics, Chalmers/Göteborg
University, S-412 96 Göteborg, Sweden
(2)Laboratoire
Collisions, Agregats, Reactivite, UMR 5589, Universite Paul Sabatier, 31062
Toulouse, cedex France
(3)Department of Chemistry and Chemical
Biology, Harvard University, Cambridge, MA 02138-2902, USA
(4)Department
of Physics and Astronomy and Department of Chemistry,University of California,
Irvine, CA 92697-4575, USA
We present a combined theoretical and experimental study of chemisorption parameters and STM images for the C2H2, C2H and C2 on Cu(001). The geometric and electronic structure, vibrational energies and STM images were obtained from density functional calculations. The calculated STM images were obtained from Kohn-Sham wave-functions using the Tersoff and Hamann approximation. The STM images and the chemisorption bonds are discussed in terms of the surface electronic structure. The experimental STM images were obtained using two different types of tips, a normal tip and a sharp tip obtained by irreversible dissociation of H$_2$S. The latter tip is shown to give an enhanced resolution. The comparison between the experimental and calculated images give a near-quantitative agreement for both types of tip at appropriate tip-surface distances. An analysis shows that protrusions that appear in all images derive from adsorbate-induced resonances at the Fermi energy. All images also exhibit a wide depression that we attribute to the screening of the electronegative adsorbates by the metal conduction electrons.