Plasmonic Modes in Au and AuAg Nanowires and Nanowire Dimers Studied by Electron Energy Loss Spectroscopy

In this chapter, we review our recent work on the investigation of surface plasmon modes in metallic nanowires and nanowire dimers by means of electron energy loss spectroscopy combined with scanning transmission electron microscopy (STEM-EELS). Due to the very high spatial resolution, STEM-EELS is a powerful technique to visualize multipole order surface plasmon modes in nanowires and study the dependency of their resonance energies on different parameters such as nanowire dimensions or nanowire porosity. In addition, we investigate surface plasmon hybridization in nanowires separated by gaps of less than 10 nm or connected by small metallic bridges. In such structures new modes arise, which depend strongly on gap or bridge sizes. Experimental results are supported by finite element simulations. The investigated nanowires and dimers are fabricated by electrodeposition in etched ion-track templates, combined with a selective dissolution processes. The synthesis techniques and their advantages for the fabrication of plasmonic nanostructures are also discussed

Host-guest supramolecular chemistry in solid-state nanopores: potassium-driven modulation of ionic transport in nanofluidic diodes

We describe the use of asymmetric nanopores decorated with crown ethers for constructing robust signal-responsive chemical devices. The modification of single conical nanopores with 18-crown-6 units led to a nanodevice whose electronic readout, derived from the transmembrane ion current, can be finely tuned over a wide range of K+ concentrations. The electrostatic characteristics of the nanopore environment arising from host-guest ion-recognition processes taking place on the pore walls are responsible for tuning the transmembrane ionic transport and the rectification properties of the pore. This work illustrates the potential and versatility of host-guest chemistry, in combination with nanofluidic elements, as a key enabler to achieve addressable chemical nanodevices mimicking the ion transport properties and gating functions of specific biological channels.Fil: Perez Mitta, Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Albesa, Alberto Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Knoll, Wolfang. Austrian Institute of Technology; AustriaFil: Trautmann, Christina. GSI Helmholtzzentrum für Schwerionenforschung; AlemaniaFil: Toimil Molares, Maria Eugenia. GSI Helmholtzzentrum für Schwerionenforschung; AlemaniaFil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentin

Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire

International audienceThe monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 µm silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced

Etched ion-track membranes as tailored separators in Li–S batteries

Lithium–sulfur (Li–S) batteries are considered a promising next generation alternative to lithium-ion batteries for energy storage systems due to its high energy density. However, several challenges, such as the polysulfide redox shuttle causing self-discharge of the battery, remain unresolved. In this paper, we explore the use of polymer etched ion-track membranes as separators in Li–S batteries to mitigate the redox shuttle effect. Compared to commercial separators, their unique advantages lie in their very narrow pore size distribution, and the possibility to tailor and optimize the density, geometry, and diameter of the nanopores in an independent manner. Various polyethylene terephthalate membranes with diameters between 22 and 198 nm and different porosities were successfully integrated into Li–S coin cells. The reported coulombic efficiency of up to 97% with minor reduction in capacity opens a pathway to potentially address the polysulfide redox shuttle in Li–S batteries using tailored membranes

Conical Nanotubes Synthesized by Atomic Layer Deposition of Al₂O₃, TiO₂, and SiO₂ in Etched Ion-Track Nanochannels

Etched ion-track polycarbonate membranes with conical nanochannels of aspect ratios of ~3000 are coated with Al₂O₃, TiO₂, and SiO₂ thin films of thicknesses between 10 and 20 nm by atomic layer deposition (ALD). By combining ion-track technology and ALD, the fabrication of two kinds of functional structures with customized surfaces is presented: (i) arrays of free-standing conical nanotubes with controlled geometry and wall thickness, interesting for, e.g., drug delivery and surface wettability regulation, and (ii) single nanochannel membranes with inorganic surfaces and adjustable isoelectric points for nanofluidic applications

Nanoscale Structuring in Confined Geometries using Atomic Layer Deposition: Conformal Coating and Nanocavity Formation

Nanoscale structuring in confined geometries using atomic layer deposition (ALD) is demonstrated for surfaces of nanochannels in track-etched polymer membranes and in mesoporous silica (SBA-15). Suitable process conditions for conformal ALD coating of polymer membranes and SBA-15 with inorganic oxides (SiO₂, TiO₂, Al₂O₃) were developed. On the basis of the oxide-coated layers, nanochannels were further structured by a molecular-templated ALD approach, where calixarene macromolecules are covalently attached to the surface and then embedded into an Al₂O₃ layer. The removal of calixarene by ozone treatment results in 1–2 nm wide surface nanocavities. Surfaces exposed to different process steps are analyzed by small angle X-ray scattering (SAXS) as well as by X-ray photoelectron and infrared spectroscopy. The proposed nanostructuring process increases the overall surface area, allows controlling the hydrophilicity of the channel surface, and is of interest for studying water and ion transport in confinement

Effects of Size Reduction on the Electrical Transport Properties of 3D Bi Nanowire Networks

3D nanowire networks are fascinating systems for future microelectronic devices. They can be handled like macroscopic objects, while exhibiting properties of nanoscale materials. Here, the fabrication of free‐standing 3D bismuth nanowire networks with well‐controlled and systematically adjusted wire diameter and interconnectivity is presented. The samples are fabricated by pulse electroplating of bismuth into the pores of ion track‐etched membranes using an aqueous electrolyte. By optimizing the growth parameters, homogeneously grown, mechanically self‐supporting and free‐standing networks without a supporting matrix are achieved. Cross‐plane Seebeck coefficient and electrical resistance values are investigated as a function of nanowire diameter and temperature. The unique characteristics of these highly interconnected and mechanically self‐supported Bi 3D nanowire networks offer exciting perspectives for their implementation in, e.g., infrared detection based on thermoelectric effects, sensing, and THz applications

ZnO Nanowire Networks as Photoanode Model Systems for Photoelectrochemical Applications

In this work, the fabrication of zinc oxide (ZnO) nanowire networks is presented. By combining ion-track technology, electrochemical deposition, and atomic layer deposition, hierarchical and self-supporting three-dimensional (3D) networks of pure ZnO- and TiO₂-coated ZnO nanowires were synthesized. Analysis by means of high-resolution transmission electron microscopy revealed a highly crystalline structure of the electrodeposited ZnO wires and the anatase phase of the TiO₂ coating. In photoelectrochemical measurements, the ZnO and ZnO/TiO₂ nanowire networks, used as anodes, generated higher photocurrents compared to those produced by their film counterparts. The ZnO/TiO₂ nanowire network exhibited the highest photocurrents. However, the protection by the TiO₂ coatings against chemical corrosion still needs improvement. The one-dimensionality of the nanowires and the large electrolyte-accessible area make these 3D networks promising photoelectrodes, due to the improved transport properties of photogenerated charge carriers and faster redox reactions at the surface. Moreover, they can find further applications in e.g., sensing, catalytical, and piezoelectric devices