Shape-controlled nanopores in single crystals

Abstract

Nanometer length-scale holes (nanopores) are often formed in amorphous materials forfundamental studies of molecular mass transport. In the current study, electron beamirradiation in the transmission electron microscope was used to form nanopores in acrystalline material (Si). Analysis of the nanopores showed that they are formed byknock-on of atoms by the high energy incident electron beam, and surface diffusion ispartially responsible for the hour-glass shapes that are found for some nanopores.Energetically favorable three-dimensional shapes of nanopores were simulated, and thenanopores simulated in the model crystalline material were found to be more stable thanthe nanopores simulated in the amorphous material. The nanopore shape was also found todepend on the nanopore diameter-to-length ratio. Based on the above, we demonstrate theadvantage in using a crystalline material for nanopore formation and show that control ofthe three-dimensional shape of nanopores formed by electron beam irradiation is possible.