Seminars

Coherent x-ray imaging of self-assembled nanoislands and other applications of synchrotron x-ray diffraction and scattering

by Alexey Zozulya (Synchrotron SOLEIL, Gif-sur-Yvette, France)

Wednesday, January 12, 2011 from to (Europe/Berlin)
at Bldg. 25b, room 109
Description
The coherent x-ray scattering (CXS) is the efficient nondestructive method of characterization of nanostuctures. In our recent studies the CXS technique has been applied to image SiGe nanoislands grown by liquid phase epitaxy on Si(001) substrate. Using highly intense and coherent x-ray beam at third-generation synchrotron, a significantly enhanced diffraction pattern can be obtained under grazing incidence conditions (GISAXS geometry) from an average island. The coherent scattering pattern represents a sum of coherent scattering signals from individual nanoislands which have narrow size distribution, identical shape, and orientation. We used iterative phase retrieval algorithms for the reconstruction of projected electron density of an island with typical dimensions in the 100 nm range. The obtained spatial resolution of less than 20 nm for such islands is not achievable by other x-ray imaging methods. 
The second part concerns the small angle X-ray scattering (SAXS) method for the study of biological macromolecules in solution. Solution SAXS provide important structural insight to a protein macromolecule under native physiological conditions (radius of gyration, molecular weight, maximum size and excluded volume) and allows for ab initio reconstruction of a shape of individual macromolecules as well as modeling of macromolecular complexes. At the X33 beamline of EMBL Hamburg at DESY the SAXS data collection system is fully automated and includes in-vacuum liquid sample cell, sample changing robot and 2D pixel detector (Pilatus 1M) as key components. Examples of structural biology studies performed using solution SAXS at the X33 beamline will be presented. 
The final part of the talk deals with the performance and applications of the DiffAbs beamline of synchrotron SOLEIL. The DiffAbs bending magnet beamline operates in 3 - 23 keV photon energy range and is dedicated to structural studies of a variety of materials by combining x-ray diffraction, x-ray fluorescence and x-ray absorption spectroscopies, with the possibility of using either standard or microfocused x-ray beam as a probe. The standard setup uses prefocusing of the x-ray beam by bendable monochromator crystal and mirrors which provides 300x300 m2 beam size at the sample position and the flux of 1011 - 1012 cps, depending on selected energy. The microbeam mode using either x-ray Fresnel zone plates or KB mirrors provides less than 10x10 m2 spot size in the 3-18 keV energy range. Scientific scope covers wide range of materials science applications such as structural characterization of thin films and nanostructures, strain and stress distribution under external load, behavior of materials at high temperatures and others.