Modeling the Reaction/Transport Behavior of the Geode Process for Semiconductor Nanowire Synthesis

The bottom-up vapor-liquid-solid (VLS) mechanism enables the growth of semiconductor nanowires with nanoscale-controlled compositions and structures. The nanowires produced using this method have shown promise, for example, as electronic devices. While nanowires are usually grown on planar substrates, for large scales of production, this is unlikely to be feasible. The Geode Process solves the issue of scalability by growing nanowires on the internal surface of hollow silica microcapsules. The goal of this study is to model the reaction /transport behavior of the Geode process, to explore the impact of key process parameters and better understand its limits. Governing equations for this process, including mass transport through the microcapsule wall and reactive consumption of precursors at the nanowire growth catalyst, are solved in MATLAB. The model shows that relatively large variations in microcapsule diameter and wall thickness have a negligible impact on nanowire growth rate. However, variations in reactor conditions, particularly temperature, can result in more substantial variations in growth rate. These findings inform the future reactor design necessary to minimize variation when scaling up the Geode process.