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Controlling the nanopore fabrication using high energy electron beam exposure

Recently there has been tremendous interest about the dynamical sequence of fabrication of the solid state nanopore due to its capability of the nanosize solid state biosensor as a single molecule sensor. Depending upon the instruments such as transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM), the dynamics of nanopore formation present different physical mechanisms. In this report, formation of the nanopores was examined. Metallic nanopores with ~ 50 nm diameter on top of the oxide pyramid were fabricated using conventional Si microfabrication techniques followed by wet isotropic etching of the oxide; sputter metal deposition followed by the focused ion beam (FIB) techniques. No shrinking phenomena were observed for the nanopore diameter greater than 50 nm under electron beam irradiation using TEM. However, for high scanning electron beam irradiation using FESEM, shrinking of the Au nanopore was always observed. We do believe that these phenomena can be attributed to the liquid phase surface modification for TEM electron beam and adiabatic solid state phase surface modification for high scanning FESEM. For a huge amount of energy input from high scan rate and the poor thermal conduction to its surrounding area, the energy spike inside the electron penetration area would occur. However, a TEM electron beam irradiation without repetitive scan can provide the liquid phase surface modification.