Condensed-Matter Physics & Materials Science Seminar

X-ray diffraction is a versatile tool to determine the structural properties of nanostructures such as size, shape, spatial distribution, chemical composition and strain. No sample preparation is needed and buried as well as uncapped objects can be studied. So far, in most x-ray studies, ensembles of nanostructures have been investigated. Consequently, the obtained parameters are those of an average structure, thus meaningful only if the ensemble has a small size dispersion.

In the first part of the lecture I will describe the techniques (mainly grazing incidence diffraction (GID) and GISAXS and report on ex-situ and in-situ studies of Ge islands grown on Si (001). I will then present a novel X-ray method to study the core of defects evolving during the island growth. Around bulk forbidden (200) reflections, the diffuse scattering from the defect induced distortions of the Si matrix is fairly suppressed, which makes it possible to study directly the diffuse scattering induced by the atomic structure of the defect cores [1].

The second part of the talk is devoted to local probe x-ray diffraction experiments on inhomogeneous nanostructured systems: a focused x-ray beam is used to localize nanostructures and analyze their strain and composition, identifying and probing individual objects one by one. In a scanning mode, an image of the sample surface is recorded, which allows the reproducible alignment of a specific nanostructure for analysis.

Two examples will be shown. i) SiGe islands on Si(001): The structural properties of specific islands are measured in diffraction and compared to the results of scanning electron microscopy on precisely the very same object [2]. 2) Rolled Up NanoTubes: I will show microdiffraction results on a single particular tube on a macroscopic sample. The lattice parameter distribution and strain were measured and modeled using elastic theory [3].

By addressing shape, strain and composition at the nanoscale, the spatial