The Geode Process: Hollow Silica Microcapsules as a High Surface Area Substrate for Semiconductor Nanowire Growth

We introduce and demonstrate critical steps toward the Geode process for the bottom-up synthesis of semiconductor nanowires. Central to the process is the design and fabrication of an unconventional, high surface area substrate: the interior surface of hollow silica microcapsules, assembled from silica particles via emulsion templating, and featuring porous walls to enable efficient gas transport. The interior surface of these hollow silica microcapsules is decorated with gold nanoparticles that seed nanowire growth via the vapor–liquid–solid (VLS) mechanism. We demonstrate the production of the necessary microcapsules and show how microcapsule structure and stability upon drying are influenced by the type of silica particles and use of a particle cross-linking agent. Finally, we demonstrate the synthesis of crystalline Si nanowires in the microcapsule interior.