Phase Separation in Single In<sub><i>x</i></sub>Ga<sub>1–<i>x</i></sub>N Nanowires Revealed
through a Hard X‑ray Synchrotron Nanoprobe
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Abstract
In
this work, we report on the composition, short- and long-range
structural order of single molecular beam epitaxy grown In<sub><i>x</i></sub>Ga<sub>1–<i>x</i></sub>N nanowires
using a hard X-ray synchrotron nanoprobe. Nano-X-ray fluorescence
mapping reveals an axial and radial heterogeneous elemental distribution
in the single wires with Ga accumulation at their bottom and outer
regions. Polarization-dependent nano-X-ray absorption near edge structure
demonstrates that despite the elemental modulation, the tetrahedral
order around the Ga atoms remains along the nanowires. Nano-X-ray
diffraction mapping on single nanowires shows the existence of at
least three different phases at their bottom: an In-poor shell and
two In-rich phases. The alloy homogenizes toward the top of the wires,
where a single In-rich phase is observed. No signatures of In-metallic
precipitates are observed in the diffraction spectra. The In-content
along the single nanowires estimated from X-ray fluorescence and diffraction
data are in good agreement. A rough picture of these phenomena is
briefly presented. We anticipate that this methodology will contribute
to a greater understanding of the underlying growth concepts not only
of nanowires but also of many nanostructures in materials science