Nanometre hole formation in MgO using electron beams

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Abstract
Square cross-sectional holes with widths of about 1 nm can be formed in MgO crystals using circular cross-section high-current-density electron probes which are focused and oriented close to . High-resolution scanning transmission electron microscopy has been used to reveal, on a unit cell scale, the three-dimensional geometry of the hole structures as they grow. The holes develop from the electron exit face of the crystal, have a profile which is clearly related to that of the electron probe, and can be generated with incident electron energies as low as 40keV. Unlike other inorganic materials, there appears to be no lower current density threshold for hole formation and there is no excess Mg or 0 present in the MgO crystal after hole formation, suggesting that the MgO is desorbed as molecules or clusters. A model for the hole formation process is proposed.