The use of ETEM in oxidation studies of carbon nanostructures such as CB has revealed new, and confirmed previously suggested, oxidation mechanisms. However, the influence of the electron beam on the dynamic oxidation processes must be well understood in order to connect the results to the real world. To date, there are few studies reporting any quantification of the effect1,2. To better understand the origin of the beam effect, we note that CB will react with oxygen primarily at so called active sites, which can be generated through atomic displacements from the primary electrons (PE) or by reaction with oxygen ionized by PE2,3 or secondary electrons (SE)4. These three mechanisms for electron beam induced oxidation are distinct and will respond differently to varying reaction and imaging conditions.

In our study, we have observed the oxidation of CB at varying electron dose rates, electron energies, sample temperatures, and gas pressure, in two ETEM setups. Data were collected using electron energy loss spectroscopy time-series for averaging over large agglomerates of particles to gain more precise oxidation rate measurements, and high-resolution image series to investigate the local effect on individual particles for mechanistic determination.

Our experiments show that in situ beam-enhanced CB oxidation is localized to the irradiated area, that the oxidation rate is not significantly affected by changes in electron energy, and that the in situ beam-enhancement in oxidation rate is saturated at higher dose rates. Additionally, the oxidation only occurs in the presence of an oxidizing gas, not in inert gases like N2. These findings contradict the common claim that oxygen ionization by PE is the driving force behind the increased oxidation rate in TEM. The saturation effect also precludes ionization by SE as an important process unless the sample is located over a SiNx support, in which case there are so many more SEs that they have a noticeable but minor impact. Atomic displacement induced active sites can explain our observations well.

Therefore, we have shown that CB oxidation is mainly affected by elastic high-energy electron-sample interactions, with a smaller contribution from inelastic electron-gas processes from secondary electrons emitted from the sample and sample support. While this process suggests that there are no safe conditions, the beam effect can be made vanishingly small compared to the intrinsic oxidation. We show how EELS can link processes seen at individual particles to whole agglomerates.

1. S. B. Simonsen, University of Copenhagen, 2008.
2. A. L. Koh and R. Sinclair, Ultramicroscopy, 2017, 176, 132–138.
3. A. D. Sediako, C. Soong, J. Y. Howe, M. R. Kholghy and M. J. Thomson, Proceedings of the Combustion Institute, 2017, 36, 841–851.
4. H. Yoshida, Y. Tomita, K. Soma and S. Takeda, Nanotechnology, 2017, 28, 195301.
StatusUnpublished - 2023 maj 1
EvenemangEuropean Materials Research Society 2023 Spring Meeting - Strasbourg, Frankrike
Varaktighet: 2023 maj 292023 juni 2


KonferensEuropean Materials Research Society 2023 Spring Meeting
Förkortad titelE-MRS 2023

Ämnesklassifikation (UKÄ)

  • Nanoteknik
  • Materialkemi


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