Diffraction at GaAs/Fe$_{3}$Si core/shell nanowires: the formation of nanofacets

TL;DR

This study investigates the formation of nanofacets on Fe$_3$Si shells of GaAs/Fe$_3$Si nanowires, revealing their structure, energetics, and effects on x-ray scattering, with implications for nanowire surface engineering.

Contribution

The paper combines experimental x-ray diffraction and DFT calculations to elucidate nanofacet formation and surface energetics in GaAs/Fe$_3$Si core/shell nanowires.

Findings

Fe$_3$Si$\{111\}$ nanofacets are confirmed by x-ray and TEM.

Nanofacets cause characteristic streaks in reciprocal space maps.

Chemical reactions occur at higher growth temperatures, affecting nanowire interfaces.

Abstract

GaAs/Fe$_{3}$Si core/shell nanowire structures were fabricated by molecular-beam epitaxy on oxidized Si(111) substrates and investigated by synchrotron x-ray diffraction. The surfaces of the Fe$_3$Si shells exhibit nanofacets. These facets consist of well pronounced Fe$_3$Si{111} planes. Density functional theory reveals that the Si-terminated Fe$_3$Si{111} surface has the lowest energy in agreement with the experimental findings. We can analyze the x-ray diffuse scattering and diffraction of the ensemble of nanowires avoiding the signal of the substrate and poly-crystalline films located between the wires. Fe$_3$Si nanofacets cause streaks in the x-ray reciprocal space map rotated by an azimuthal angle of 30{\deg} compared with those of bare GaAs nanowires. In the corresponding TEM micrograph the facets are revealed only if the incident electron beam is oriented along [1$\overline{1}$0] in accordance with the x-ray results. Additional maxima in the x-ray scans indicate the onset of chemical reactions between Fe$_{3}$Si shells and GaAs cores occurring at increased growth temperatures.