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Center for Nonlinear Studies |
The controlled formation of carbon nanostructures is key to the reliable production of carbon-based device components in, e.g., electronics, filtration, and composite materials. The conditions for synthesis, including how the catalytically active region evolves over time, determines structure, yield, and purity of the final products. In chemical vapor deposition – the most common mode of synthesis of carbon structures – elongation and contraction of catalytic nanoparticles occurs, as was first reported more than a decade ago. Here, we demonstrate using in situ, real-time imaging and modeling that catalytic nanoparticles are driven through a thermodynamic cycle of elongation and contraction. As a tubular structure grows, the particle elongates due to a favorable metal-carbon interaction that overrides the increased surface energy of the metal. The formation of subsequent nested tubes, however, drives up the surface energy relative to the interaction energy until the overall free energy balance becomes unfavorable, and then the particle exits the tube and the cycle repeats. Since the particle reshaping is universal for different metals, particle sizes, carbon structures, etc., our quantitative approach – including predictive expressions – helps unravel the different observations and brings us closer to practical optimization of these processes for desired end products.
Host: Kirill A Velizhanin