***NOTE: CHANGE IN DATE AND TIME***

***TUESDAY, November 17, 2009***

The dynamics of atoms and molecules adsorbed on surfaces play a crucial role in many fundamentally and technologically important processes. Surprisingly, rather little is currently known about the mechanism of such motion, since a full description requires information on both nanometre lengthscales and picosecond timescales - an extremely challenging combination. I will describe several recent measurements which reveal novel mechanisms of surface diffusion. Alkali metals on Cu(001) provide a simple geometry where we have explored the balance between adsorbate-substrate and adsorbate-adsorbate forces and the subsequent effect on motion. The data has been used to construct empirical potentials representing the alkali-surface interaction and as a test of interaction force models. We also observe an entirely unexpected form of three dimensional motion at higher coverages. While large alkali atoms are well described using classical "over-barrier" models, in the contrasting case of hydrogen we observe a transition to a thru-barrier tunnelling mechanism at low temperatures. We compare the experimental data with recent proton-bandstructure calculations and thru-barrier tunnelling rate models, and relate the experimental features to the coherence of such quantum transport processes.
Refreshments at 12:00 pm
Courtesy of IAMDN

Host: Jane Hinch