AVS 51st International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThA

Paper SS3-ThA1
Molecular Transport on the Nano-Second Timescale; Co/cu(001).

Thursday, November 18, 2004, 2:00 pm, Room 213B

Session: Surface Diffusion and Transport
Presenter: G. Alexandrowicz, University of Cambridge, UK
Authors: G. Alexandrowicz, University of Cambridge, UK
A.P. Jardine, University of Cambridge, UK
H. Hedgeland, University of Cambridge, UK
P. Fouquet, Institut Laue-Langevin, France
S. Dworski, University of Cambridge, UK
W. Allison, University of Cambridge, UK
J. Ellis, University of Cambridge, UK
Correspondent: Click to Email
The measurement of surface diffusion on microscopic length scales presents a considerable experimental challenge. Measurements are typically restricted to specific systems which either diffuse sufficiently slowly for real time techniques, such as STM, to be applied or fast enough to be seen using Quasielastic Helium Atom Scattering (QHAS). Here, we present the first surface diffusion measurements from the unique new Cambridge @super 3@He Spin Echo Spectrometer@footnote 1@@footnote 2@. The apparatus makes use of the @super 3@He Spin Echo technique@footnote 3@ to improve upon existing QHAS resolution by three orders of magnitude, showing new insights into previously inaccessible experimental regimes. We have studied the prototypical molecular system; CO/Cu(100). Existing QHAS measurements on this system were very limited@footnote 4@ and the intense debate over the difference between potential energy surfaces extracted from the measurements and from first principle calculations@footnote 5@ was left unresolved. Our measurements show the system is diffusing well within the previously unmeasurable regime. Quasielastic broadenings were measured as function of momentum transfer and temperature and interpreted using MD simulations. The analysis reveals a Potential Energy Surface, illustrating the success and limitations of recent first principle calculations@footnote 6@, and serves as a bench mark for further theoretical improvements. @FootnoteText@ @footnote1@ AP Jardine, P Fouquet , S Dworski, G Alexandrowicz, J Ellis, W Allison, To be published @footnote2@ S Dworski, G Alexandrowicz, P Fouquet, AP Jardine, W Allison, J Ellis. Rev. Sci. Inst. In press. 2004. @footnote3@ C Shmidt, D Scholz, U Spinola, M Dekivit, D Dubbers. Phys. Rev. Lett. 75(10):1919-1922 @footnote4@ AP Graham, JP Toennies, Surf. Sci. 427-428 (1999) @footnote5@ Q G, DA King, J. Chem. Phys. 114(2001) 1053 @footnote6@ P Fouquet, RA Olsen, EJ Baerends, J. Chem. Phys. 119(2003) 509-514.