Macroscopic networks of nanowires: fabrication and properties

Juan J. Vilatela

IMDEA Materials, Madrid, Spain

Juanjose.vilatela@imdea.org

The talk provides an overview of the synthesis of high aspect ratio nanowires/nanotubes, their assembly as macroscopic networks and the relation between network structure and bulk properties (mechanical, electrochemical, optical).

Through floating catalyst chemical vapour deposition (FCCVD) in a flow-through process, nanowires (or nanotubes) can be grown at orders-of-magnitude higher faster rate than conventional substrate-based processes. The resulting nanowire high aspect ratio > 100 and relatively high throughput (100s mg/h) enable assembly as macrosocopic network materials in formats such as electrodes, membranes and ordered arrays of interest for bulk studies and applications. The method, originally applied to growth macroscopic network materials of CNTs, BNNTs, has been more recently applied by our group to synthesise SiNWs,¹ SiCNWs,² and MOx NWs,³ respectively.

We study the macrokinetics of the FCCVD process applied to SiNW growth from gold catalyst as a model system to identify the factors controlling nanowire aspect ratio and process efficiency. We find that catalyst efficiency is close to 100 % and that silane-to-silicon conversion scales with the total surface of catalyst in the gas phase. Kinetic parameters are obtained for catalysed SiNW growth and for homogeneous Si nanoparticle formation in the absence of catalyst, as well as for wall deposition. Avenues for throughput increase are through a larger total catalyst surface and higher effective precursor concentration by preventing wall deposition through reactor re-design.

Next, the talk presents our efforts to study nanowire aggregation in the gas phase, and the formation of macroscopic network materials. We study the agglomeration of Si nanowires by scanning electron microscopy of samples taken from the gas downstream of the reaction zone, and through simulations with a Brownian collision algorithm to form agglomerate models. In the experimental analysis no individualized NWs are found, only agglomerates, which is consistent with the fast binary collision rates of 0.24 s estimated.  The agglomerates show “fractal” scaling, with a fractional dimension Df of 1.8 and agglomerate size increasing with the number of nanowires to the power of 1/Df, consistent with a diffusion limited cluster aggregation process. Formation of a nanowire aerogel involves percolation of agglomerates, therefore occurring at much lower volume fraction than for individualized particles considering excluded volume theory.(5)

Finally, we show that networks of entangled nanowires can be visualized as nanotextiles both in terms of their structure and their bulk mechanical properties. They are flexible in bending, sustain large strains, have inherent damage-tolerance and are dominated by inter-, rather than intra-particle features, particularly their orientation distribution function.

Two properties of nanowire networks are also briefly discussed: their electrochemical properties as high-capacity electrodes in either Li-ion(6) or Na-ion batteries, free of binder or conductive additives; and their optical properties as aligned arrays produced from liquid crystal dispersions.  

(1) Schäufele, R. S.; Vazquez-Pufleau, M.; Vilatela, J. J. Tough Sheets of Nanowires Produced Floating in the Gas Phase. Mater. Horizons 2020, 7 (11), 2978–2984.

(2) Gómez-Palos, I.; Vazquez-Pufleau, M.; Valilla, J.; Ridruejo, Á.; Tourret, D.; Vilatela, J. J. Ultrafast Synthesis of SiC Nanowire Webs by Floating Catalysts Rationalised through In-Situ Measurements and Thermodynamic Calculations; Nanoscale, 2022.

(3) Gómez-Palos, I.; Vazquez-Pufleau, M.; Schaeufele, R. S.; Mikhalchan, A.; Pendashteh, A.; Ridruejo, A.; Vilatela, J. J. Gas-to-Nanotextile: High-Performance Materials from Floating 1D Nanoparticles. Nanoscale 2023.

(4) Isabel Gómez-Palos, Álvaro Ridruejo  and  Juan J. Vilatela. Sequential control of catalyst alloying and oxygen-mediated nucleation for continuous synthesis of SnO nanowires floating in the gas phase. Nanoscale, 2025, https://doi.org/10.1039/D5NR01257K

(5) Nabil Abomailek, Isabel Gómez‐Palos, Cristian Carnicero, María Murillo, Richard Schäufele, Rulan Qiao, Adam Boies & Juan J. Vilatela - Fractal Scaling in the Gas‐Phase Agglomeration of Nanowires. Small 2409673, 2025. DOI: 10.1002/smll.202409673

(6) Afshin Pendashteh, Rafael Tomey and Juan J. Vilatela - Nanotextile 100% Si anodes for thenext generation energy-dense Li-ion batteries. Advanced Energy Materials , 2304018, 2024. DOI: 10.1002/aenm.202304018