Abstract

The dynamics of Xenon on Platinum (111) have been measured using the 3He spin-echo (3HeSE) spectrometer, recently developed in our group [1, 2]. 3HeSE has given a significant improvement in energy resolution for the measurement of surface dynamics. In this study we take advantage of this development to fully characterise the system of Xe on Pt(111) which has previously been only partially accessible, leaving perplexing questions. A previous time of flight, quasielastic helium atom scattering (QHAS) study presented evidence for a fully mobile two-dimensional gas at low coverage [3]. In the present work, we perform a detailed, lineshape analysis of the quasielastic scattering to reveal evidence for two dynamic processes of isolated Xe species. Diffusion as a two dimensional gas is apparent, which supports the previous study. However, we also find evidence of an activated jump diffusion process. The signature for jump diffusion is demonstrated by a second, and significantly narrower, broadening in the energy spectrum. The jump diffusion component can be resolved in the present work due to the improved resolution of 3HeSE over QHAS . Using the low friction previously predicted [4], we suggest that Xe settles into preferred sites with finite lifetime and when activated travels relatively large distances across the potential energy surface.

[1] A.P. Jardine, S. Dworski, P. Fouquet, G. Alexandrowicz, D. J. Riley, G. Y. H. Lee, J. Ellis, W. Allison, Science 304, 1790-1793 (2004). [2] P. Fouquet, A.P. Jardine, S. Dworski, G. Alexandrowicz, W. Allison, and J. Ellis, Rev. Sci. Instrum. 76, 053109 (2005). [3] J.Ellis, A.P. Graham, J.P.Tonnies, Phys. Rev. Lett. 82, 5072-5075 (1999). [4] B.N.J. Persson and A. Nitzan, Surf. Sci. 367, 261 (1996)