We present a versatile method to fabricate conical nanopores of different materials and shapes on silicon/silicon nitride chips for various nanoscale applications. We drilled silicon nitride membranes coated with photoresist with Focused Ion Beam (FIB) calibrated to the desired shape, followed by atomic layer deposition of a dielectric oxide and subsequent photoresist removal and annealing. We obtained conical nanopores made of SiO2 and Al2O3 on a silicon nitride membrane. We characterized the samples electrically, with Scanning Electron Microscopy (SEM), cross sections and Energy-Dispersive X-ray spectroscopy (EDX). We studied concave, straight, and convex nanopore shapes and measured their ionic current rectification effects, which vary with the nanopore geometry. We supported our experimental findings with numerical simulations based on the Poisson-Nernst-Planck model. With the addition of a metallic layer, we conducted enhanced Raman spectroscopy experiments to confirm the capacity of our structures to perform as tailored plasmonic antennas. Our results confirm the robustness and tunability of this fabrication method to produce conical nanopores of dielectric oxides for a wide range of applications and the potential of controlling the nanopore geometry.
Due to their superior properties in single-molecule detection, plasmonic and nanopore-based sensors have attracted research interest. In recent times, they have been combined in a single device, resulting in plasmonic nanopores-based sensors. These solid-state devices featured unprecedented enhancements in single-molecule and nanoparticle detection, optical spectroscopies and trapping, control of local temperature. In this context, we have investigated two kinds of nanostructures: plasmonic nanopores and plasmonic nanoantennas, both of which were fabricated on free-standing Si3N4 membranes. As regards the nanopores, we were able to prove that their plasmonic coating enhanced their conductance when illuminated at 631 nm. On the other side, antenna-shaped nanopores (i.e., nanoantennas) were fabricated via plasmonic photochemical deposition. At this regard, we demonstrated that it was possible to fabricate nanoantennas with different internal diameters by different time of plasmon-induced photochemical deposition of metal precursors at the free tip of the nanoantenna. In conclusion, we proved that it was possible to use each nanoantenna (i.e., each decreasing internal diameter) to detect the translocation of nanoparticles with correspondingly decreasing diameters or of DNA.
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