Solid-state nanopore membranes have been investigated for over two decades due to their interesting applications for chemical- and bio- sensing, nano-electronics, nano-fluidics, and ultra-filtration. To realize these applications, excellent control over the shape and size of the pores in the membranes is required. This seminar will discuss the fabrication, characterization, and application of versatile nanopores in silicon dioxide and silicon nitride membranes. These materials provide a chemically and mechanically robust platform for solid-state nanopores and allow easy integration into silicon-based microelectronics.
Silicon dioxide and silicon nitride free-standing membranes were fabricated by depositing thin films of these materials on Si wafers and selectively removing the substrate using standard micro-electro-mechanical systems processing. Both track-etch technology and controlled dielectric breakdown (CDB) have been studied to fabricate nanopores in these membranes. For the former, the membranes were irradiated with swift heavy ions at the 14UD accelerator, ANU (Australia), at DC-60 Cyclotron (Kazakhstan), and at the UNILAC linear accelerator, GSI Helmholzzentrum für Schwerionenforschung (Germany). The irradiation leads to the formation of ion tracks which are subsequently etched using appropriate etchants in a custom-built etching cell to form conical or hourglass-shaped nanopores. Using the CDB technique, single nanopores are fabricated in 6 nm, 10 nm, and 25 nm thick Si3N4 membranes. Additionally, the fabrication of single nanopores in thick (100 nm and 200 nm) Si3N4 membranes using a combination of swift heavy ion irradiation and CDB was investigated. The characterization of nanopores in these membranes has been performed using scanning electron microscopy, atomic force microscopy, small-angle X-ray scattering as well as conductometry measurements.
We have achieved unprecedented control over the nanopore shape and size through the proper characterization of these nanopore membranes. Nanopores of different sizes (length can be varied from 6 nm to 2000 nm) and shapes (half cone angles can be varied from ~7° to ~54°) can now readily be fabricated according to the requirement of the applications. We are currently evaluating these nanopore membranes for different applications. First promising results studying the charge and size separation of charged dyes as well as gas sensing by coating the nanopore surface using chitosan will be presented. Furthermore, experiments using single nanopores fabricated using the CDB technique to detect single molecules of different biomarkers will be shown. The annealing behavior of the ion tracks in silicon dioxide thin films and its influence on nanopore shape will also be discussed during the seminar as well as future prospects for the nanopore membranes.
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