Tunnel current measurement of MgO and MgO/Fe/MgO nanoregions during TEM observation

Conductance measurements of nanostructures with simultaneous transmission electron microscopy (TEM) were performed on thin insulating MgO films (2–3 nm thick) and MgO/Fe/MgO tri-layer films (2 nm/1 nm/2 nm) deposited on tip-shaped Au electrodes. A movable counter electrode was used to choose nanoscale regions with contact areas smaller than 10 nm2 for investigation. Systematic measurements on MgO films taken by keeping contact with the counter electrode provided a tunnelling barrier height of about 1.4 eV. The conductance of an MgO/Fe/MgO double junction composed of Fe nanoparticles showed the Coulomb-blockade-like characteristics at room temperature. The threshold voltage breaking the Coulomb blockade corresponded to the value estimated from the geometry observed by TEM.