2, The European Synchrotron, Grenoble, , France
3, Paul-Drude-Instit für Festkörperelektronik, Berlin, , Germany
4, Charles University in Prague, Prague, , Czechia
Combination of coherent x-ray diffraction imaging (CXDI) and ptychograpy in Bragg geometry was used in order to determine the structural homogeneity of single core-shell-shell heterostructure nanowires (NWs) grown on (111) silicon substrate. The NWs were composed by 140nm GaAs core-10nm In0.10Ga0.90As inner shell and 30nm GaAs outer shell and are 2-3 micron in length. The experiment has been performed at beamline ID01 of the ESRF, Grenoble using coherent x-rays with the energy of 9keV and a beam size of 150x200nm2 full width at half maximum (FWHM). CXDI was applied to record 3D reciprocal space maps (RSM) of the symmetric GaAs (111) reflection at different positions along the NW growth axis for two different NWs. In case of NW1 the 3D RSMs taken along the NW growth axis are same except the bottom part, revealing a rather uniform NW structure. On the other hand for NW2 the RSMs display local nonuniformities, because they are changing as a function of NW height. In addition to CXDI measurements, the very same NWs were investigated with 2D ptychography at the GaAs (111) Bragg reflection. In agreement with the RSM analysis ptychography reconstruction also shows the homogeneous structure (reconstructed homogeneous phase) at NW1 but phase change along the growth axis at NW2.