Catalyst–substrate interaction and growth delay in vapor–liquid–solid nanowire growth

Abstract

Understanding of the initial stage of nanowire growth on a bulk substrate is crucial for the rational design of nanowire building blocks in future electronic and optoelectronic devices. Here, we provide in situ scanning electron microscopy and Auger microscopy analysis of the initial stage of Au-catalyzed Ge nanowire growth on different substrates. Real-time microscopy imaging and elementally resolved spectroscopy clearly show that the catalyst dissolves the underlying substrate if held above a certain temperature. If the substrate dissolution is blocked (or in the case of heteroepitaxy) the catalyst needs to be filled with nanowire material from the external supply, which significantly increases the initial growth delay. The experiments presented here reveal the important role of the substrate in metal-catalyzed nanowire growth and pave the way for different growth delay mitigation strategies.

Temperature effect on Al predose and AlN nucleation affecting the buffer layer performance for the GaN-on-Si based high-voltage devices

“…Given that the bulk diffusivity of Al in Si is low compared to the surface diffusivity of silicon, and that the solubility limit of Al in Si is very low (<0.05% at temperatures ⩽1000 °C48) ), it is plausible to expect that the liquid AlSi phase is formed via surface diffusion of both silicon and aluminum atoms and by consumption of the substrate atoms. 49) The former process is, hence, responsible for the distortion of the step edges around larger islands due to Si consumption. Formation of larger Al islands is favorable at higher temperatures (HT samples), where the surface diffusivity of aluminum atoms is larger, however, difference in temperature only cannot explain the absence of step edge distortion at LT samples.…”

Development of in situ characterization techniques in molecular beam epitaxy

“…For instance, SEM provides better performance, compared to STM with a more limited observation field, when adatom diffusion lengths become significant during high-temperature growth. Homma et al have used SEM to study the effects of changes in adatoms at the kink points of atomic steps during crystal growth [55] . SEM can also observe the growth process, including island growth, coalescence, and completion of monolayer growth.…”

A controlled nucleation and growth of Si nanowires by using a TiN diffusion barrier layer for lithium-ion batteries

“…[13][14][15][16] The unintentionally formed alloy, composed of Au and metal entities, contaminates the catalysts as nucleation sites; hence, the nucleation of Si NWs is delayed at these sites, and Si is consumed by silicide formation. 13 Template-assisted growth to minimize the formation of Si islands and aggregates requires the preparation of templates such as anodized aluminum oxide (AAO) layers on current collectors. Typical AAO-assisted growth of Si NWs involves additional steps of Al deposition, anodization, electrodeposition of Au seed layers, and etching of the sacricial AAO layers.…”

“…11 Although the formation of metal silicide layers and bulk-like Si structures can be reasonably mitigated by controlling growth conditions 10 and implementing template-assisted growth 12 especially Au nanoparticles, for VLS growth of NWs, tend to form alloys with substrate materials. [13][14][15][16] The unintentionally formed alloy, composed of Au and metal entities, contaminates the catalysts as nucleation sites; hence, the nucleation of Si NWs is delayed at these sites, and Si is consumed by silicide formation. 13 Template-assisted growth to minimize a formation of Si islands and aggregates requires preparation of templates such as anodized aluminum oxide (AAO) layers on current collectors.…”