Sputtering and the formation of nanometre voids and holes in aluminium in a scanning transmission electron microscope

Abstract

Abstract Nanometre voids and holes have been produced in aluminium films up to 220nm thick by the stationary focused 100 keV high-current-density electron probe in a dedicated scanning transmission electron microscope. The electron energy is below the threshold for bulk displacements in aluminium but is sufficient to cause sputtering of aluminium atoms from the electron-exit surface. The sputtering leads to the formation of a pit with a diameter determined by the electron probe size at the electron-exit surface. As the pit aspect ratio increases, atoms are sputtered from the pit base onto the pit side walls where they experience a much reduced electron intensity, rather than being sputtered directly out of the pit. Eventually the pit seals to leave a void, separated from the end of the small pit that remains at the electron-exit surface. By repeatedly interrupting the irradiation so as to image a projection of the irradiated volume, it is shown that the void then moves from near the electron-exit surface ...