Examining Dynamic Behaviors in Carbon Nanotube Growth

In situ TEM enables the direct evaluation of catalytic processes at appropriate temperature and pressure conditions.

Artist impression showing growth of carbon nanotubes via an iron-catalyzed process.

Artist impression showing growth of carbon nanotubes via an iron-catalyzed process.

Application of Carbon Nanotubes

Carbon nanotubes (CNTs) hold significant potential, for example, in biomedical devices, photovoltaics, high-performance catalysis, and energy storage.

While CNTs are now produced on an industrial scale, it is still challenging to control the chirality, diameter, and length of CNTs.

This is mainly because of the lack of understanding of growth mechanisms at a molecular level and the absence of atomic information on growth dynamics of CNTs.

Huang et al. from FHI Berlin and ETH Zürich have recently carried out an in situ TEM study of CNT growth. The growth and termination dynamics of CNTs have been disclosed in atomic detail under appropriate conditions.

DENSsolutions Nano-Reactor for Atomic-Scale Observation

Real-time observation at an atomic-scale was enabled by the stability of the DENSsolutions Nano-Reactor and the ability to introduce stimuli such as heating and gas:

In Situ TEM video made using the DENSsolutions Climate system, showing Fe-catalyzed multiwalled carbon nanotube growth. Temperature: 800 °C, pressure: 178.65 mbar, diluted H2 + C2H4.

The researchers were able to disclose the effect of temperature and pressure on the growth of CNTs utilizing in situ TEM gas and heating. Studies in the past were conflicted regarding the active state of the catalyst.

With live investigations of CNT growth at appropriate conditions, researchers could show not only the active phase of the catalyst but also the complex structural dynamics of the catalyst throughout the process of CNT growth.

In this study, the Nano-Reactor, the core of the DENSsolutions Climate In Situ TEM system, was employed as a carrier for the Fe2O3 sample (precursor material for CNT growth). As a pre-treatment, this was then heated in a diluted hydrogen gas flow.

The in situ experiment began at 150 °C and was followed by a gradual increase up to 800 °C in a gas mixture of H2, C2H4 and He.

To make catalyst research more efficient, the DENSsolutions Climate system can be provided with an exclusive Gas Supply system that allows instant switching between gases and accurate control over the gas mixture ratio.

Between 450 °C and 650 °C, the reduction of Fe2O3 to Fe3O4 was accompanied by a collapse of larger particles into smaller ones.

Between 450 °C and 650 °C, the reduction of Fe2O3 to Fe3O4 was accompanied by a collapse of larger particles into smaller ones.

Thanks to the development of the MEMS-based gas flow Nano-Reactor, we are allowed to perform in situ experiments inside the chamber of the TEM at relevant conditions. Using the Climate system from DENSsolutions, we have recently carried out a detailed In Situ study on the growth behaviors of CNTs at realistic conditions. On the basis of the real-time observations, we are able to reveal the active structure of the working catalyst and its dynamic re-shaping during the course of CNT growth. Extended observations further reveal three different scenarios for the growth termination of CNTs at the atomic-scale. The presented work provides important insights into understanding the growth and termination mechanisms of CNTs and may serve as an experimental basis for rational design and controlled synthesis of CNTs.

Dr. Xing Huang, First and Corresponding author, ETH Zürich

Acknowledgments

Produced from materials originally authored by Xing Huang, Ramzi Farra, Robert Schlögl and Marc-Georg Willinger from FHI Berlin and ETH Zürich.

This information has been sourced, reviewed and adapted from materials provided by DENSsolutions.

For more information on this source, please visit DENSsolutions.

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