Transition from elastic to plastic strain release in core−shell nanowires revealed by in-plane x-ray diffraction

Abstract

We investigate the strain evolution and relaxation process as function of increasing lattice mismatch between the GaAs core and surrounding In x Ga 1−x As shell in core-shell nanowire heterostructures grown on Si(111) substrates. The dimensions of the core and shell are kept constant whereas the indium concentration inside the shell is varied. Measuring the 224 and 220 in-plane Bragg reflections normal to the nanowire side edges and side facets, we observe a transition from elastic to plastic strain release for a shell indium content x>0.5. Above the onset of plastic strain relaxation, indium rich mounds and an indium poor coherent shell grow simultaneously around the GaAs core. Mound formation was observed for indium contents x=0.5 and 0.6 by scanning electron microscopy. Considering both the measured radial reflections and the axial 111 Bragg reflection, the 3D strain variation was extracted separately for the core and the In x Ga 1−x As shell.

Bending and reverse bending during the fabrication of novel GaAs/(In,Ga)As/GaAs core–shell nanowires monitored by in situ x-ray diffraction

“…Alternatively, In situ diffraction using high brilliance monochromatic x-rays at synchrotron radiation facilities serves as an ideal technique to investigate strain and the bending evolution [22,23] of nanowires due to its high sensitivity to atomic displacement in the angstrom range [16,26], and changes in the lattice orientation that are not even visible by a scanning electron microscope [27]. Moreover, XRD provides information about bending in 3D real space, and can be performed on nanowire ensembles for meaningful statistical study since nanowires grown on a common substrate exhibit slightly different structural properties due to different local growth conditions such as competition for growth species by neighboring nanowires [28].…”