Voltage-Gated Ion Transport through Semiconducting Conical Nanopores Formed by Metal Nanoparticle-Assisted Plasma Etching

Teena James†, Yevgeniy V. Kalinin†, Chih-ChiehChan†, Jatinder S. Randhawa†, Mikhail Gaevski§, andDavid H. Gracias*†‡

^†Department of Chemical and Biomolecular Engineering and ^‡Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States

^§ Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl300673r

Publication Date (Web): June 22, 2012

Copyright © 2012 American Chemical Society

Nanopores with conical geometries have been found to rectify ionic current in electrolytes. While nanopores in semiconducting membranes are known to modulate ionic transport through gated modification of pore surface charge, the fabrication of conical nanopores in silicon (Si) has proven challenging. Here, we report the discovery that gold (Au) nanoparticle (NP)-assisted plasma etching results in the formation of conical etch profiles in Si. These conical profiles result due to enhanced Si etch rates in the vicinity of the Au NPs. We show that this process provides a convenient and versatile means to fabricate conical nanopores in Si membranes and crystals with variable pore-diameters and cone-angles. We investigated ionic transport through these pores and observed that rectification ratios could be enhanced by a factor of over 100 by voltage gating alone, and that these pores could function as ionic switches with high on–off ratios of approximately 260. Further, we demonstrate voltage gated control over protein transport, which is of importance in lab-on-a-chip devices and biomolecular separations.