Physical and Analytical Chemistry Seminar
Lecturer: Dr. Nadav Avidor
Location: Faculty Seminar Room
Helium Atom Scattering (HAS) offers some unique properties for studying surfaces, but is considered to lack general mechanisms for chemical contrast. In search for such a mechanism, I am exploring the idea of Motion Based Chemical Contrast (MBCC): the dynamics parameters of individual species may serve as surface-specific signature with which one can chemically analyse a multi-species system. Recent results from a computational study on bi-species system suggest that at dilute adsorbate densities, the inter-cell (“slow”) diffusion can be sufficient for resolving the partial density of adsorbate from the total line-shape, and at higher surface densities, the intra-cell motion, which is less sensitive to inter-adsorbate interactions, can reveal the partial density.
In the talk, I will introduce Helium Spin Echo spectroscopy [1,2] which enables us to measure the ultra-fast molecular dynamics at the surface. I will then present a few case-studies of single-species measurements, to demonstrate how and why the surface dynamics can be a useful fingerprint of the adsorbates. Lastly, I will discuss in more details results from my recent computational study which suggest that MBCC may indeed be feasible.
 Progress in Surface Science, 84(11-12), pp.323-379 (2009)
 Journal of Physics: Condensed Matter, 19(30), p.305001 (2007)