Stephane Labat1 Marie-Ingrid Richard2 1 Sara Fernandez1 2 Maxime Dupraz3 Marc Verdier3 Guillaume Beutier3 Marc Gailhanou1 Jérôme Carnis1 Pascal Gentile4 Joel Eymery4 Tobias Schulli2 Olivier Thomas1

1, CNRS- Aix-Marseille Université, Marseille, , France
2, ID01-ESRF, Grenoble, , France
3, CNRS-Univ Grenoble Alpes, Grenoble, , France
4, CEA, Grenoble, , France

Semiconductor nanowires (NWs) are promising nanostructures to achieved better photonic and electronic properties for later nanotechnologies applied in e.g. catalysis, microelectronics (nanosensors and nanotransistors), photonics and optical devices. Nevertheless defects and diffuse interfaces influence their properties.
As a first step, the defects as Inversion Domain Boundaries (IDBs) are investigated for GaN NWs with coherent X-ray diffraction in Bragg conditions. Several Bragg reflections have been measured at different heights of the wires using a nano-focused beam. Combined with phase retrieval algorithms, coherent X-ray diffraction yields non-destructive displacement field mapping with a spatial resolution better than 10 nm and a displacement accuracy of a few picometer.1 The absolute polarity of the domains was unambiguously revealed. A rigid relative displacements of the domains and the absence of microscopic strain away from the IDBs were evidenced. Moreover, both, the IDBs configuration and the displacement field evolve along the wire. Additionally, the influence of the Si content will be discussed.
As a second step, the results on interdiffusion in Ge-Si Core-Shell NWs will be presented. Both, surface and interfacial structures are considered as the influencing factors on the enhanced emission efficiency of core-shell heterostructures at the nanoscale.2 Notably, the short diffusion distances make nano-sized objects very susceptible to degradation. To follow atomic diffusion in individual Ge-Si core-shell NWs, In situ Bragg Coherent Diffraction Imaging was performed at certain stages to probe the evolution of the strain and compositional gradients in the interior of the NWs as a function of temperature up to 850°C. The occurrence of intermixing will be discussed considering the initial shape of the core.

1 S. Labat, et al., ACS Nano 9, 9210 (2015).
2 L. J. Lauhon, et al., Nature 420, 57 (2002).