Nanopore fabrication by low flux FIB is primarily driven by sputter erosion. On average, each ion impact from a focused ion beam sputters between two and three target atoms from a typical silicon specimen, eventually thinning the target membrane and forming a through-thickness nanopore. At low flux, the formation rate is thus proportional to the ion flux. However, detailed simulation results suggest that multiple ions, if delivered at a fast enough rate, can significantly accelerate hole formation via a new mechanism.

At slightly higher fluxes than typically employed in experiments, the target material heats up faster than it cools via thermal conduction. This leads to local melting and explosive boiling of the target material. Mass is rapidly rearranged via bubble growth and coalescence, leading to material removal that is orders of magnitude faster than that occurring by sputter erosion. The high flux beam thus provides a shortcut to overcoming the energy barrier associated with nanopore formation.

By this new mechanism, sputtering no longer limits nanopore formation rate, something that could provide a way of greatly accelerating this process. The necessary beam fluxes can be produced using modern FIB systems, and we hope that experiments will be performed soon to study this new mechanism.

The researchers published their work in the journal Nanotechnology 25 035303

Further reading

Simple pulling process creates nanopore for single-molecule sensing (Apr 2011)
Bio-functionalization resizes FIB fabricated nanopores (May 2010)
FIB patterning controls position and dimensions of quantum dots (Apr 2012)
FIB mills single-nanowire plasmonic gratings (Jun 2012)