Microstructural evolution in self-catalyzed GaAs nanowires during in-situ TEM study

Abstract

The microstructural evolutions in self-catalyzed GaAs nanowires (NWs) were investigated by using in situ heating transmission electron microscopy (TEM). The morphological changes of the self-catalyst metal gallium (Ga) droplet, the GaAs NWs, and the atomic behavior at the interface between the self-catalyst metal gallium and GaAs NWs were carefully studied by analysis of high-resolution TEM images. The microstructural change of the Ga-droplet/GaAs-NWs started at a low temperature of ∼200 °C. Formation and destruction of atomic layers were observed at the Ga/GaAs interface and slow depletion of the Ga droplet was detected in the temperature range investigated. Above 300 °C, the evolution process dramatically changed with time: The Ga droplet depleted rapidly and fast growth of zinc-blende (ZB) GaAs structures were observed in the droplet. The Ga droplet was completely removed with time and temperature. When the temperature reached ∼600 °C, the decomposition of GaAs was detected. This process began in the wurtzite (WZ) structure and propagated to the ZB structure. The morphological and atomistic behaviors in self-catalyzed GaAs NWs were demonstrated based on thermodynamic considerations, in addition to the effect of the incident electron beam in TEM. Finally, GaAs decomposition was demonstrated in terms of congruent vaporization.

Real-time thermal decomposition kinetics of GaAs nanowires and their crystal polytypes on the atomic scale

“…22,23,28–31 And, secondly, conventional growth of NWs combined with subsequent transfer for ex situ decomposition and analysis, mostly by heating NWs inside a TEM. 32–35 The first approach enables best quality of the NWs because contamination and oxidation of the surfaces is prevented. It also enables studies of the influence of growth parameters, not only of temperature but also of pressure, e.g.…”

“…Specifically, an amorphous shell of native oxide can form on the NWs during transfer, which is more stable against thermal decomposition than the studied material itself and can locally even prevent decomposition. 33,35,39,40 In addition, in such experiments, the NW is lying on the support film and has a different heat contact to the substrate, which can lead to non-uniform decomposition, 33–35,41 unlike decomposition inside conventional growth environments. 22,23 Moreover, several thermal decomposition studies performed on NWs using in situ TEM were influenced by other extrinsic features, such as the inherent Au-catalyst droplet often used for the growth.…”

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

“…Beyond this temperature, the arsenic shell desorbs with an activation energy of ∼2.32 eV, leading to clean facets of the NW core, which supports the success of this approach to promote the subsequent epitaxial growth of an oxide shell. This work demonstrates that the capping/decapping process is efficient to obtain clean GaAs nanowire surfaces (stable until 600 °C) and could be suitable for other arsenide NWs such as InAs (stable until 380 °C). The proposed method allows us to obtain clean facets in the high vacuum of a TEM column and UHV setups equipped with a heater, thus opening the way to surface science studies on arsenide NWs.…”

Microscopic Understanding of the Growth and Structural Evolution of Narrow Bandgap III–V Nanostructures

“…When temperature was increased above 300 °C, the volume of the Ga droplet decreased rapidly, and thr fast growth of ZB GaAs structures can be observed in the droplet. Finally, the decomposition of GaAs began at the WZ region and propagated to the ZB region at ~600 °C [ 79 ].…”