Münster 1997 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
O: Oberflächenphysik
O 40: Methodisches (Theorie)
O 40.2: Vortrag
Freitag, 21. März 1997, 11:30–11:45, BOT
Correlation function measurements in surface overlayers at equilibrium — •M.I. Larsson1, M.C. Tringides2, H. Pfn"ur1, H. Frischat1, K. Budde1, and M. Henzler1 — 1Institut f"ur Festk"orperphysik, Universit"at Hannover, Appelstr.2, D-30167 Hannover — 2Department of Physics, Iowa State University, Ames IA 50011, USA
The study of dynamic phenomena in surface overlayers (i.e. surface diffusion, dynamic critical phenomena) can be carried out with diffraction by measuring intensity fluctuations. The signal corresponding to the physical process of interest is usually mixed with statistical noise. We examine the role of the gatetime τ (in digital mode acquisition typical of diffractometers) and the length collection time necessary to recover a weak signal out of statistical noise. For a given gaussian distribution G(t), which describes the time interval between counts, we generate a signal train of counts by sampling the distribution either randomly (to generate statistical noise) or within a narrow neighbourhood δ (to generate a correlated signal). By varying the relative probability of sampling (either random or bias) we generate signal trains of different signal-to-noise (S/N) ratios. We show that there is an optimal choice of τ, otherwise a higher decay constant is measured by the autocorrelation function. More importantly, we find the relationship T α (S/N)−1.7 for the aquisition time T needed to recover the same quality correlation function for different S/N ratios.