Direct observations of plasma-nanomaterial interaction enabled by in situ Transmission Electron Microscopy*

Microplasma, known for its stability and high reactivity at atmospheric pressure, offers a promising alternative to conventional technologies. Therefore, it has been utilized in various fields such as material synthesis, etching, deposition, and redox processes. However, the direct observation and understanding of these processes have been limited by challenges in developing in situ diagnostic tools. Our recent efforts established an in situ plasma TEM (Transmission electron microscope) capability with a spatial resolution of less than 1 nm. By incorporating micron-sized electrodes in a gas environmental TEM cell, we generated a stable atmospheric microplasma within the TEM. This overcomes the vacuum requirements of the TEM and the microscale and high-voltage needs of NTP in the cell. Our spatial resolution is about 100 times smaller than a similar study performed a decade ago to observe gold sputtering by argon plasma.

We demonstrate the new capability through real-time observation of morphological changes in Fe₃O₄ nanoparticles under DC hydrogen microplasma (He/H₂, 0.5%) with a temporal resolution of ~1 s. The changes are likely due to a reduction process caused by reactive species, particularly hydrogen atoms. This technique has the potential to enhance our understanding of plasma-material interactions and broaden the potential for in situ TEM studies in the NTP field.