Fig. 2.

Validation of the proposed operation principle. a TEM image of the MgO crystal flakers synthesized by hydrothermal method. b The MgO flakers did not change after being exposed to a 300 keV, 0.1 A/cm² e-beam irradiation for 14 min. c The introduction of 2 Pa CO₂ atmosphere leads the reaction, i.e. MgO + CO₂→MgCO₃, occurred violently. The final product is that the MgO flakers were transformed into a piece of amorphous product with many bubbles in it. d After being heated to 400 °C in vacuum for 2 min, the amorphous product was crystallized. The inset selected area electron diffraction (SAED) pattern shows that it is nanocrystalline MgCO₃. e–h Surface evolution of a FIB-fabricated Mg pillar during the exposure in 2 Pa CO₂ and e-beam irradiation. TEM images showing transformation process of the native oxide layer to the compact nanocrystalline MgCO₃&MgO layer. Scale bars: d 200 nm, h 10 nm