Jun 21, 2012
Conductometric measurements reconstruct nanopore profiles
Narrow nanopores with diameters down to less than 10 nm can be fabricated by selective etching of ion tracks in dielectrics. Typically, it is assumed that the pores are conical. In other words, a symmetric pore would consist of two intersecting cones with a small aperture in the centre of the membrane. Whereas an asymmetric pore would consist of a truncated cone with its tip pointing in the direction of etch attack. In a recent study, published in the journal Nanotechnology, scientists have shown that both profiles are overly simplified.
The researchers explain that much more realistic profiles can be derived by measuring the electrical current throughout the etching process, in particular during the initial stages of perforation. The reconstruction is free of geometric assumptions. It reflects a highly soluble zone close to the ion track axis that extends up to 10 nm and a radiation-hardened zone, which can be up to 100 nm. The constriction is about 1 µm long and has a diameter below 100 nm, which was supported by high-resolution scanning electron microscopy data.
The revised geometry is relevant for nanodevices. The mobility of molecules depends critically on the constriction diameter and the tapering angle of the pore. Thanks to the reconstruction algorithm suggested by the team, these critical parameters can be accurately determined. Furthermore, immobilized charges at the pore wall define the interaction of the solute, its adsorption and the molecules dwell time in the pore.
The technique has far-reaching consequences for applications in nanofluidics, molecular sensors, current rectification and chemical valves.
Full details can be found in the journal Nanotechnology.
About the author
Pavel Apel is deputy head of the Centre of Applied Physics at the Flerov Laboratory in Dubna. His work focuses on the application of micro and nanostructures based on ion tracks. Reimar Spohr is a consultant in ion track technology. In 2001, the team fabricated the first diode-like single track pore. Now they have reunited to study the relationship between geometrical and electrical properties of the nanopore. Oleg Orelovich is head of the Electron Microscopy Group at the Flerov Laboratory in Dubna. He contributed high-resolution scanning electron microscopy observations and was supported by Bozena Sartowska, lecturer at the Warsaw Institute of Nuclear Chemistry and Technology. Irina Blonskaya contributed high-resolution electroconductivity measurements of single and multiple ion tracks.