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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P309
Static Speckle Experiments using White Synchrotron Radiation
Tushar P. Sant 1 , Tobias Panzner 1 , Wolfram Leitenberger 2 , Gudrun
Gleber 1 , Ullrich Pietsch 1
1 Institute for Physics, University of Siegen, Walter Flex Str. 3, D-57068 Siegen. –
2 Institute for Physics, University of Potsdam, Am Neuen Palais 10, D-14469 Potsdam.
We have performed static speckle experiments using white synchrotron radiation at
EDR beamline at BESSY II. Static speckle pattern gives access to spatially resolved
height function of the illuminated area at the atomic length scale [1]. It has been shown
that for coherent scattering experiments in reflection geometry the knowledge of the
illumination function incident on the sample is important for the reconstruction of the
surface morphology from speckle data[1]. The coherent reflectivity has been recorded
from the surface of technologically smooth GaAs wafer (Fig.1). Besides periodic oscillations
which are caused by the scattering from incident pinhole other features appear
in the measurement of the real surface of the sample. The illumination function calculated
by means of Lommel formalism matches well with the measured function for
the pin-hole diameter of 11.4 µm and will be used for further surface reconstruction
from speckle maps. For further examination speckle map of reflection from a laterally
periodic structure like GaAs grating is studied. Here the sample is illuminated
with coherent as well as incoherent radiation by using pinholes of different diameters.
Incoherent illumination confirms the existence of grating peaks. Under coherent illumination
the grating peaks split into speckles which correspond to fluctuations on
the sample surface. The surface morphology of the grating is reconstructed from this
coherent scattering so as to determine local height fluctuations.
[1] I. A. Vartanyants et.al., Phys. Rev. B 55 (1997) 13193.
Fig. 1: Measured coherent
reflectivity from
GaAs wafer
Fig. 2: Calculated
and measured illumination
function at
10keV