Laboratoire de Physique des Interfaces et des Couches Minces

CNRS - École polytechnique - Institut Polytechnique de Paris

In-situ ETEM Studies of Fe Catalyst NPs Formation under Molecular or Radicals/Activated Hydrogen Environments for the Growth of SWCNTs

Written by : José Barroit

Contributors: Ileana Florea (LPICM), Mariam Ezzedine (LPICM), Mihai-Robert Zamfir (LPICM), Loan Truong (LPICM), Eleonor Caristan (LPICM) and Costel – Sorin Cojocaru (LPICM)

The present study is focused on the realization of in situ TEM observations of Fe catalyst film dewetting and catalytic nanoparticles (NPs) formation under molecular and/or radical/ activated hydrogen environments. The formed NPs exhibit different sizes depending on the temperature and type of reactive gas. The experiments are performed within a modified environmental transmission electron microscope-ETEM equipped with a Cs image aberration-corrector; a special sample holder and customized CVD gas sources that allow sending collimated beams of molecules/radicals with different partial pressure.From the experimental point of view the analysis of the recorded images at different temperatures and exposure times allowed us to observe that the Fe film dewetting is strongly related to both the nature of the hydrogen environment and the temperature conditions. Thus, through the in-situ TEM heating process under 3sccm (1.4 10-4 mbar) of molecular H2 environment, we notice that the Fe film dewetting starts at 400°C leading to the formation of big crystalline Fe nanoparticle (Figure 1). We have observed that the Fe NPs size increases, 20nm size, as the temperature increases while keeping the same H2 flow. On the contrary, under 6sccm (2.5 10-3mbar) activated hydrogen environment the Fe film dewetting initiate only at a higher temperature, around 500°C with the formation of smaller crystalline Fe Nps with sizes ranging from 1nm up to 5nm(Figure 2). The formation of such small nanoparticles is related to the presence of hydrogen radicals which tend to block the metal atoms surface diffusion by creating small defects within the support which pin the forming nanoparticle and prevent their agglomeration.

This work is funded by the French state managed by the National Research Agency under the GIANT  project ANR-18-CE09-0014 and Investments for the Future program under the references ANR-10-EQPX-50 pole NanoMax.

I. Florea et al.  Microscopy and MicroanalysisVolume 27Supplement S2: Proceedings of CISCEM 2021 – the 5th Conference on In-Situ and Correlative Electron Microscopy, November 2021, pp. 85 – 86; DOI:



Figure 1. In situ TEM analysis of Fe film dewetting through a heating process under 3sccm molecular H2 environment illustrating the formation of Fe NPs.




Figure 2. In situ TEM analysis of Fe film dewetting through a heating process under 6sccm activated H2 environment illustrating the formation of small Fe metallic NPs.