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O: Oberflächenphysik

O 12: Methods

O 12.7: Vortrag

Montag, 27. März 2006, 16:30–16:45, WIL B321

The influence of sample properties and finite resolution on the results of surface-XPCS measurements — •Robert Fendt¹, Christian Gutt², Aymeric Robert³, Anders Madsen³, and Metin Tolan¹ — ¹Exp. Physik 1a, Univ. Dortmund — ²HASYLAB, Hamburg — ³ESRF, Grenoble, France

Surface-sensitive XPCS is a powerful technique for in-situ measurements on a fluctuating surface. However, recent experimental results clearly show that assuming the Fraunhofer limit (which holds in the case of PCS) is an over-simplification in the case of XPCS, yielding the need for a new theoretical treatment [1, 2]. In the case of low-viscosity liquids, which is considered here, one expects an oscillating behaviour (due to capillary waves) of the correlation function, i. e. for a homodyne setup, G_hom(q^→,τ)= 1+Ccos²(ω(q^→)τ)exp(−2Γ(q^→)τ) with the contrast 0<C≤ 1. However, under special circumstances, a “heterodyne” function G_het(q^→,τ)= 1+Ccos(ω(q^→)τ)exp(−Γ(q^→)τ) is observed [3, 4]. This behaviour can be understood as a resolution effect, i. e., a finite experimental resolution dq>0 enables the specular reflection from the surface to function as a static reference signal [2]. Surprisingly, recent experiments [3] suggest a possible dependence of dq on the sample material. This would essentially mean that the usual separation of specular and off-specular scattering might not be valid in the case of SXPCS.

[1] M. Sprung et al.: ESRF 2004, unpub.

[2] T. Gadheri: PHD thesis, to be publ.

[3] R. Fendt et al.: ESRF 2005, unpub.

[4] C. Gutt et al.: PRL 91, 076104 (2003)