Insights into the Arsenic Shell Decapping Mechanisms in As/GaAs Nanowires by X-ray and Electron Microscopy

Nanowire heterostructures of the oxide (shell)-semiconducting (core) type are of interest for various applications in energy harvesting, such as electrodes for photocatalysis and in sensors. Their complete synthesis often requires the deposition of the shell and the core in two separate reactors, with the risk of exposing the core to oxidation from atmospheric conditions during transfer. Here, we study the desorption mechanisms and protection efficiency of an arsenic shell, which was purposely deposited on the GaAs core for protection against undesirable oxidation. Using in situ heating in transmission electron microscopy and synchrotron radiation scanning photoelectron microscopy, we explore the morphology, structure, and surface chemistry of GaAs nanowires capped with an arsenic shell, from room temperature to 500 degrees C. A phase transformation from amorphous to polycrystalline arsenic is evidenced at a temperature of about 300 degrees C, alongside the disappearance of the surface oxidation observed at room temperature. At higher temperatures, the arsenic shell desorbs with an activation energy of 2.32 eV, leading to clean facets. These results are helpful to determine pathways toward improving the efficiency of oxidation-protective layers on III-V semiconducting nanostructures.