Münster 1997 – wissenschaftliches Programm
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O: Oberflächenphysik
O 40: Methodisches (Theorie)
O 40.7: Vortrag
Freitag, 21. März 1997, 12:45–13:00, BOT
Time-dependent phenomena on surfaces measured from diffraction intensity equilibrium fluctuations? — •M.I. Larsson2, M.C. Tringides1, H. Pfn"ur2, H. Frischat2, K. Budde2, and M. Henzler2 — 1Department of Physics, Iowa State University, Ames IA 50011, USA — 2Institut f"ur Festk"orperphysik, Universit"at Hannover, Appelstr.2, D-30167 Hannover
Time-dependent equilibrium phenomena in surface overlayres can be studied by measuring the time autocorrelation of thermally generated equilibrium fluctuations. Surface diffusion at equilibrium and dynamic critical phenomena can be analyzed in such experiments. The potential use of diffraction intensity fluctuations is examined by considering the role of incoherent summation over the finite beam size, statistical noise and signal collection time. In diffraction experiments, where the incident current probe density is kept constant, the fluctuations related to the physical process and statistical noise increase as N1/2, where N=(Lb/Lc)2 is the number of incoherent regions (Lb is the beam size and Lc is the coherence length of the diffractometer). In deciding the optimal beam size Lb a compromise should be reached between maximizing relative fluctuations but without increasing statistical fluctuations so that no impractically long collection times are needed. Different surface diffraction techniques (SPA-LEED, He-scattering, and X-ray glancing angle scattering) will be compared. These considerations will be illustrated with Monte Carlo simulations modelling thermal fluctuations