  Nanoprobe X-ray diffraction (nXRD) using focused synchrotron radiation is a
powerful technique to study the structural properties of individual
semiconductor nanowires. However, when performing the experiment under ambient
conditions, the required high X-ray dose and prolonged exposure times can lead
to radiation damage. To unveil the origin of radiation damage, we compare nXRD
experiments carried out on individual semiconductor nanowires in their as grown
geometry both under ambient conditions and under He atmosphere at the
microfocus station of the P08 beamline at the 3rd generation source PETRA III.
Using an incident X-ray beam energy of 9 keV and photon flux of
10$^{10}$s$^{-1}$, the axial lattice parameter and tilt of individual
GaAs/In$_{0.2}$Ga$_{0.8}$As/GaAs core-shell nanowires were monitored by
continuously recording reciprocal space maps of the 111 Bragg reflection at a
fixed spatial position over several hours. In addition, the emission properties
of the (In,Ga)As quantum well, the atomic composition of the exposed nanowires
and the nanowire morphology are studied by cathodoluminescence spectroscopy,
energy dispersive X-ray spectroscopy and scanning electron microscopy,
respectively, both prior to and after nXRD exposure. Nanowires exposed under
ambient conditions show severe optical and morphological damage, which was
reduced for nanowires exposed under He atmosphere. The observed damage can be
largely attributed to an oxidation process from X-ray induced ozone reactions
in air. Due to the lower heat transfer coefficient compared to GaAs, this oxide
shell limits the heat transfer through the nanowire side facets, which is
considered as the main channel of heat dissipation for nanowires in the
as-grown geometry.
