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

Abstract

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.

Gas-to-nanotextile: high-performance materials from floating 1D nanoparticles

“…Synthesis of SiNWs in laboratory-scale fluidised bed reactors with a scalable process based on silica nanoparticles resembling geodes has been recently demonstrated. 73 Specifically concerning FCCVD, the oldest scaled-up example is VGCF production. Industrial-grade VGCFs have been available for decades at relatively large industrial facilities with a reported capacity of tens of tons per site as early as 2001.…”

Programming Semiconductor Nanowire Composition with Sub-100 nm Resolution via the Geode Process

“…“Microgeode” powders are formed upon VLS growth of semiconductor nanowires on the microcapsule interiors. To date, the synthesis of microcapsule and Si nanowire microgeode powders has been demonstrated …”

“…The Geode process 28 offers a route to increase manufacturing throughput by leveraging the high surface area of silica microcapsule powders while also maintaining the ability to program nanowire composition via the VLS mechanism. Silica microcapsules exhibit porous walls to facilitate gaseous precursor transport and are lined on their interior with the metal nanoparticles that catalyze VLS growth.…”

“…To date, the synthesis of microcapsule and Si nanowire microgeode powders has been demonstrated. 28 Synthesizing nanowires with precise structural and compositional encoding via the Geode process depends on the rate of heat and mass transport through the microcapsule wall. Mass transport is governed by microcapsule wall thickness and porosity, whereas heat transport is governed by the thermal conductance of the microcapsule wall, which depends on its composition (i.e., silica) as well as thickness and porosity.…”

Bottom-up nanoscale patterning and selective deposition on silicon nanowires

“…Moreover, the bottom-up nature of all process steps-VLS nanowire growth, SCALES, and selective deposition-also ensures compatibility with the 3D nature of the nanowires themselves as well as any scalable nanowire manufacturing technique with which they may be produced (e.g. Geode Process [31], Aerotaxy [32]).…”