Formation of Nanopore-Arrays by Plasma-based Thin FilmDeposition Page: 2 of 11
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Currently methods of producing nanoscale pores in membranes have important
limitations. One method of fabricating holes with dimension of tens of nanometers is to
use electron-beam lithography, followed by reactive-ion etching. But achieving smaller
feature sizes is difficult, and because the process includes resist exposure and etching it is
slow. Holes directly milled by focused ion beam (FIB) are limited in dimension to the
beam diameter, which is about 10 nm, and arrays of apertures must be drilled one
aperture at a time. Molecular-scale nanopores in silicon nitride (Si3N4) films have been
reported using the technique of ion-beam scuplting2: apertures with an initial diameter of
100 nm were fabricated in a free-standing Si3N4 membrane supported on a silicon frame.
Irradiating the holes with a 3-keV argon ion (Ar+) beam caused them to close rather than
open up, resulting in nanopores 2 to 3 nm in diameter, as controlled by a feedback
monitoring circuit. However, this technique can only be applied to insulating membrane,
such as Si3N4 and silicon dioxide (SiO2), and multiple simultaneous nanopores have not
been reported using ion-beam sculpting. Another method of fabricating nanopores is to
use a dual beam system employing an FIB and a scanning electron microscope (SEM)4.
Apertures ranging from 50 nm to 600 nm in diameter are premachined using an FIB,
followed by gas-assisted deposition using an FIB/SEM dual beam. Depositing a film of
metal like platinum around the edges of the aperture makes them smaller and smaller.
Like the ion-beam sculpting technique, forming multiple nanopore arrays with FIB/SEM
is very slow.
In this letter, we describe a simple method of forming nanopore arrays by simultaneously
shrinking apertures of micrometer dimensions using plasma-based thin-film deposition.
As shown in Figure 1, a metallic thin film such as copper or nickel is deposited on a
substrate placed in a plasma. Over time, the size of an aperture in the substrate gradually
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Ji, Qing; Chen, Y.; Jiang, Ximan; Ji, Lili & Leung, K. N. Formation of Nanopore-Arrays by Plasma-based Thin FilmDeposition, report, March 18, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc902676/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.