Retrieving chemical and structural properties of nanomaterials through synchrotron x-ray diffraction techniques

Abstract

This thesis presents a study about crystalline semiconductor nanostructures using x-ray diffraction techniques, mainly resonant (anomalous) x-ray diffraction, in order to determine structural and chemical properties of these structures. Our first experimental result is a study about In(Mn)As islands grown under controlled Mn flux on the top of GaAs(001) substrates. Adding distinct amounts of Mn on the growth process makes the In(Mn)As islands allocate the metallic atoms in different sites, which can be substitutional or interstitial. Performing x-ray diffraction measurements on these nanostructures, using photons with energy near the Mn-K absorption edge, it is possible to verify quantitatively their chemical concentration, and also which site is being occupied. Each possible site has its own signature on different reflections and, with the right choice of reflections, one can determine, unambiguously, the percentage of occupied sites. The second study applies resonant x-ray diffraction on nanostructures of Ge grown on Si (substrate) with different miscut angles with respect to the (001) direction. It is well known from the literature that Ge can grown on Si as domes or superdomes, depending on the amount of Ge content. It is also known that a miscut angle can affect the growth dynamics, as it changes the internal composition of the structures. The quantitative study of the domes/superdomes composition carried out there connects its chemical properties with the effects observed by x-ray diffraction due to the miscut. Finally, we also present a study of InGaAs islands on top of an ultrathin GaAs(001) membrane. Nano-focused x-ray diffraction measurements allows the determination of the strain status on isolated islands, helping to understand the structural changes on the membrane after releasing it from the substrate where it was originally grown.