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Journal of the Electrochemical Society 170(2), 022506 (2023). doi:10.1149/1945-7111/acbba4, Published by IOP Publishing, Bristol

Inorganic pyrophosphate (PPi) is an important biological functional anion and plays crucial roles in life science, environmental science, medicine, and chemical process. Quantification of PPi in water has far-reaching significance for life exploration, disease diagnosis, and water pollution control. The label-free quantitative detection of PPi anions with a nanofluidic sensing device based on a conical single nanochannel is demonstrated. The channel surface is functionalized with a synthetic PPi receptor, triazol-methanaminium-functionalized pillar[5]arene (TAMAP5), using carbodiimide coupling chemistry. Due to the specific binding between TAMAP5 and PPi, the functionalized nanochannel can discriminate PPi from other inorganic anions with high selectivity through ionic current recording, even in the presence of various interfering anions. The current response exhibits a linear correlation with PPi concentration in the range from 1 × 10

In situ small angle X-ray scattering (SAXS) measurements of ion track etching in polycarbonate foils are used to directly monitor the selective dissolution of ion tracks with high precision, including the early stages of etching. Detailed information about the track etching kinetics and size, shape, and size distribution of an ensemble of nanopores is obtained. Time resolved measurements as a function of temperature and etchant concentration show that the pore radius increases almost linearly with time for all conditions and the etching process can be described by an Arrhenius law. The radial etching shows a power law dependency on the etchant concentration. An increase in the etch rate with increasing temperature or concentration of the etchant reduces the penetration of the etchant into the polymer but does not affect the pore size distribution. The in situ measurements provide an estimate for the track etch rate, which is found to be approximately three orders of magnitude higher than the radial etch rate. The measurement methodology enables new experiments studying membrane fabrication and performance in liquid environments.

The performance of free-standing parallel-aligned nanowire arrays and interconnected networks of single-crystalline cuprous oxide (Cu2O) coated with titanium oxide (TiO2) as photocathodes for solar energy harvesting was analyzed. The nanostructures were synthesized by electrodeposition in polymer membranes prepared by ion-track technology. To enhance the photoelectrochemical stability of the nanowires in aqueous solution, they were conformally coated with a 10 nm thick TiO2 layer by atomic layer deposition. The diameter, size, geometry and number density of the parallel nanowires were systematically varied. The generated photocurrents show a clear increase as a function of wire diameter and wire number. In turn, the photocurrent does not get larger with increasing wire length. Highly interconnected networks of nanowires under 45° from various directions enabled further increase of wire density number and exhibited higher photocurrent densities compared to parallel arrays.

Advanced functional materials 32(6), 2108556 (2022). doi:10.1002/adfm.202108556, Titanium dioxide (TiO$_2$) is an excellent candidate material for semiconductor metal oxide-based substrates for surface-enhanced Raman scattering (SERS). Biotemplated fabrication of TiO$_2$ thin films with a 3D network is a promising route for effectively transferring the morphology and ordering of the template into the TiO$_2$ layer. The control over the crystallinity of TiO$_2$ remains a challenge due to the low thermal stability of biopolymers. Here is reported a novel strategy of the cellulose nanofibril (CNF)-directed assembly of TiO$_2$/CNF thin films with tailored morphology and crystallinity as SERS substrates. Polymorphous TiO$_2$/CNF thin films with well-defined morphology are obtained by combining atomic layer deposition and thermal annealing. A high enhancement factor of 1.79 × 10$^6$ in terms of semiconductor metal oxide nanomaterial (SMON)-based SERS substrates is obtained from the annealed TiO$_2$/CNF thin films with a TiO$_2$ layer thickness of 10 nm fabricated on indium tin oxide (ITO), when probed by 4-mercaptobenzoic acid molecules. Common SERS probes down to 10 nm can be detected on these TiO$_2$/CNF substrates, indicating superior sensitivity of TiO$_2$/CNF thin films among SMON SERS substrates. This improvement in SERS sensitivity is realized through a cooperative modulation of the template morphology of the CNF network and the crystalline state of TiO$_2$., Published by Wiley-VCH, Weinheim

The use of track-etched membranes allows further fine-tuning of transport regimes and thus enables their use in (bio)sensing and energy-harvesting applications, among others. Recently, metal-organic frameworks (MOFs) have been combined with such membranes to further increase their potential. Herein, the creation of a single track-etched nanochannel modified with the UiO-66 MOF is proposed. By the interfacial growth method, UiO-66-confined synthesis fills the nanochannel completely and smoothly, yet its constructional porosity renders a heterostructure along the axial coordinate of the channel. The MOF heterostructure confers notorious changes in the transport regime of the nanofluidic device. In particular, the tortuosity provided by the micro- and mesostructure of UiO-66 added to its charged state leads to iontronic outputs characterized by an asymmetric ion current saturation for transmembrane voltages exceeding 0.3 V. Remarkably, this behavior can be easily and reversibly modulated by changing the pH of the media and it can also be maintained for a wide range of KCl concentrations. In addition, it is found that the modified-nanochannel functionality cannot be explained by considering just the intrinsic microporosity of UiO-66, but rather the constructional porosity that arises during the MOF growth process plays a central and dominant role.

Description, Novel sensors can not only detect SARS-CoV-2 or other viruses in real-world samples but also determine if they are infectious., Viral infections are a major global health issue, but no current method allows rapid, direct, and ultrasensitive quantification of intact viruses with the ability to inform infectivity, causing misdiagnoses and spread of the viruses. Here, we report a method for direct detection and differentiation of infectious from noninfectious human adenovirus and SARS-CoV-2, as well as from other virus types, without any sample pretreatment. DNA aptamers are selected from a DNA library to bind intact infectious, but not noninfectious, virus and then incorporated into a solid-state nanopore, which allows strong confinement of the virus to enhance sensitivity down to 1 pfu/ml for human adenovirus and 1 × 104 copies/ml for SARS-CoV-2. Applications of the aptamer-nanopore sensors in different types of water samples, saliva, and serum are demonstrated for both enveloped and nonenveloped viruses, making the sensor generally applicable for detecting these and other emerging viruses of environmental and public health concern.

During the last few years, much scientific effort has been devoted to the control of ionic transport properties of solid state nanochannels and the rational integration of chemical systems to induce changes in the ionic transport by interaction with selected target molecules for (bio)sensing purposes. In this work, we present the construction and functional evaluation of a highly sensitive dopamine-responsive iontronic device by functionalization of bullet-shaped track-etched single nanochannels in PET membranes with poly(3-aminobenzylamine) (PABA). The variety of basic groups in this amino-appended polyaniline derivative allows programming of the ion selectivity of the channel by setting the pH conditions. On the other hand, the amino-pendant groups of PABA become suitable binding sites for the selective chemical reaction with dopamine, leading to a change in the nanochannel surface charge. Thus, the exposure of the PABA-modified nanochannel to dopamine solutions selectively produces changes in the iontronic response. By rationally selecting the conditions for both the dopamine binding step and the iontronic reading, we obtained a correlation between the rectification efficiency and dopamine concentration down to the nanomolar range, which was also successfully interpreted in terms of a simple binding model.

In this talk we will first present the synthesis of free-standing, stable gold nanowire network with controlled morphology and geometry by ion-track technology and electrodeposition. Etched ion-track membranes with interconnected nanochannels are produced by sequential GeV heavy ion irradiation of polymer foils from four directions, and subsequent etching and enlargment of the created ion-tracks. Au nanowire networks with three different nanowire diameters are synthesized by potentiostatic electrodeposition in the templates. Nanowire growth rate and homogeneity are tuned by varying the deposition potential. The electrochemical surface area was determined for each sample by CV analysis of surface oxide reduction reaction charge transfer. We will also discuss the catalytic performance of these Au nanowire networks towards methanol electro-oxidation, acting as an electrode in a half-cell setup. High current density and high catalytic activity were recorded. The Au nanowire networks provided up to 200 times higher peak current density than a flat Au electrode, along with excellent long term cyclability, which the current density drops only 5% over 200 CV cycles. SEM studies of the morphology and crystallinity of the nanowires before and after the methanol oxidation reaction will also be presented in the talk. Figure 1. (a) SEM image of Au nanowire network, (b) Cyclic Voltammograms recorded for a of Au nanowire network in 0.1 M KOH with (solid line) and without (dash line) 1 M MeOH. Figure 1

During the last decades, researchers have demonstrated in many inspiring and creative ways that electrodeposition is an essential and versatile technology to fabricate tailored nanostructures relevant to many different applications. The combination of excellent know-how on how electrodeposition parameters influence and control the composition, morphology and structure of the resulting materials, as well as applying inventive approaches using tailored and complex substrates, templates, and new methodologies, have resulted in a plethora of three-, two-, one- and zero-dimensional materials and coatings of many different compositions and combinations. This talk will provide an overview of remarkable advances achieved in designing and synthesizing nanostructured materials by electrodeposition, especially for energy applications, such as electrodes for batteries, photo- and electrocatalysis, and thermoelectrics, and discuss the upcoming perspectives and challenges in the field.

Bismuth nanowires are excellent model systems to investigate the interplay of various size-dependent transport phenomena relevant for applications in thermoelectrics, spintronics or catalytics. Due to the large Fermi wavelength (lFermi~40 nm) and mean free paths of charge carriers (le and lph ~100 nm) in bismuth at room temperature, the influence of size-effects on the transport properties can be observed on nanowires of rather large diameters. Furthermore, these properties are also influenced by the fact that bismuth belongs to the class of topological insulator materials that exhibit special charge carrier transport on the material surface linked to topological states. To better understand the transport behavior, it is of utmost importance to control the nanowire properties like surface-to-volume ratio, wire diameter and wire morphology, crystal structure, material composition and, in case of nanowire assemblies, their relative alignment to one another. We present the synthesis of parallel and interconnected assemblies of bismuth nanowires with both cylindrical and conical geometry, and sizes ranging between 50 and 3500 nm. The wires are produced by electrodeposition in polymeric etched ion-track templates applying pulsed plating and an aqueous electrolyte of bismuth chloride. The electrodeposition process as well temperature-dependent Seebeck coefficient and electrical resistance measurements as a function of nanowire size and geometry will be discussed. Figure 1

Metal-organic frameworks (MOFs) are a novel type of nanoporous materials that have attracted widespread attention over the past two decades [1]. Cu-based metal-organic frameworks such as Cu3(BTC)2 (also known as HKUST-1) are one of the most famous MOF representatives, which exhibit a huge open porosity and thus a remarkably capacity to store and uptake different gases [2, 3]. Recently, increasing efforts are devoted toward finding synthetic routes that enable downsizing MOF crystals to the nanoscale. Achieving control over the size and shape of nanoMOFs and finding ways to assemble them is essential for their exploitation in integrated devices such as sensors, gas separation membranes or photoelectrodes. In this study we explore the conversion of free-standing arrays Cu nanowires with controlled diameter and length synthesized by electrodeposition in etched ion-track membranes into HKUST-1. In a first process step, free-standing Cu wires are produced by dissolving the ion-track polymer template. In a second step, the wires are converted into HKUST-1 structures by electrochemical oxidation. Applying 2.5 V versus a Cu counter electrode, the Cu nanowires are oxidatively dissolved and the MOF is built up as the as-formed Cu2+ ions bind to the BTC3− ligands in the electrolyte solution. The morphology and crystallinity of the samples at different transformation stages is investigated by scanning electron microscopy (Fig. 1) and transmission electron microscopy, respectively. X-ray diffraction spectra measured at different conversion times reveal the appearance of the characteristic reflections of HKUST-1. These results will be compared with previous studies of the transformation of Cu nanowires to HKUST-1 nanowires inside the polymer membrane [4]. Figure 1: SEM images of cylindrical Cu nanowires (a) before and (b) during the electrochemical conversion process, and (c) of a representative octahedral particle after complete conversion to HKUST-1. References [1] Freund R, Canossa S, Cohen SM, Yan W, Deng et al. Angewandte Chemie International Edition. (2021) 2: 23946-23974 [2] Chui SS-Y, Lo SM-F, Charmant JP, Orpen AG, Williams ID. Science. (1999) 283:1148-50. [3] Li H, Li L, Lin R-B, Zhou W, Zhang Z, Xiang S, et al. EnergyChem. (2019) 1:100006. [4] Caddeo F, Vogt R, Weil D, Sigle W, Toimil-Molares ME, Maijenburg AW. ACS applied materials & interfaces . (2019)11:25378-87. Figure 1

Enantiomers of various drug molecules have a specific effect on living organisms. Accordingly, developing a sample method for the efficient and rapid recognition of chiral drug enantiomers is of great industrial value and physiological significance. Here, inspired by the structure of ion channels in living organisms, we developed a chiral nanosensor based on an artificial tip-modified nanochannel system that allows efficient selective recognition of chiral drugs. In this system, l-alanine-pillar[5]arenes as selective receptors were introduced on the tip side of conical nanochannels to form an enantioselective "gate". The selective coefficient of our system toward R-propranolol is 4.96, which is higher than the traditional fully modified nanochannels in this work.

Advanced electronic materials 0, 2001069 (2021). doi:10.1002/aelm.202001069, Published by Wiley-VCH Verlag GmbH & Co. KG, Weinheim

The increase of energy demand added to the concern for environmental pollution linked to energy generation based on the combustion of fossil fuels has motivated the study and development of new sustainable ways for energy harvesting. Among the different alternatives, the opportunity to generate energy by exploiting the osmotic pressure difference between water sources of different salinities has attracted considerable attention. It is well-known that this objective can be accomplished by employing ion-selective dense membranes. However, so far, the current state of this technology has shown limited performance which hinders its real application. In this context, advanced nanostructured membranes (nanoporous membranes) with high ion flux and selectivity enabling the enhancement of the output power are perceived as a promising strategy to overcome the existing barriers in this technology. While the utilization of nanoporous membranes for osmotic power generation is a relatively new field and therefore, its application for large-scale production is still uncertain, there have been major developments at the laboratory scale in recent years that demonstrate its huge potential. In this review, we introduce a comprehensive analysis of the main fundamental concepts behind osmotic energy generation and how the utilization of nanoporous membranes with tailored ion transport can be a key to the development of high-efficiency blue energy harvesting systems. Also, the document discusses experimental issues related to the different ways to fabricate this new generation of membranes and the different experimental set-ups for the energy-conversion measurements. We highlight the importance of optimizing the experimental variables through the detailed analysis of the influence on the energy capability of geometrical features related to the nanoporous membranes, surface charge density, concentration gradient, temperature, building block integration, and others. Finally, we summarize some representative studies in up-scaled membranes and discuss the main challenges and perspectives of this emerging field., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Tryptophan enantiomers (d/l-Trp) were introduced into artificial nanochannels to regulate the chiral selective transport of Aβ proteins. The l-Trp channel performs effectively selectivity for the transport of Aβ protein, which would provide a new perspective for the pathological studies of Alzheimer's disease.

Nanofluidic field-effect transistors (nFETs) have attracted attention from the scientific community due to their remarkable level of control over ionic transport. Particularly, the combination of nanofluidic systems and electroactive polymers has demonstrated to be an interesting approach to achieve an electrochemically addressable device. In this work, the development of nFETs based on the integration of electropolymerized poly-o-aminophenol (POAP) films into track-etched nanochannels is proposed. The electropolymerization of POAP on the tip side of Au-sputtered asymmetric PET nanochannels not only allowed having a programmable tip diameter but also offered a precise and very rapid control of ionic transport by switching an external bias voltage. Moreover, the system exhibited a reversible behaviour between non-selective and anion-selective states. We believe that this work provides new tools and concepts to design and build high-performance nanofluidic field-effect transistors working under electrochemically controlled conditions., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

We present a systematic study of the evolution of chemically etched ion tracks formed in thermally grown a-SiO2 after irradiation with 1.1 GeV and 185 MeV Au ions. The irradiated material was subsequently etched with 2.5% hydrofluoric acid (HF) for different times yielding hollow conical shaped structures of various sizes. The characterisation of these structures was carried out by synchrotron-based small-angle X-ray scattering (SAXS) measurements, enabling the determination of the geometry and dimensions of the etched conical structures with sub-nanometre precision. The results indicate that the track etching behavior is influenced by the ion energy, and that at short etching times the latent track damage in the radial direction becomes significant.

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.

Molecular design of biosensors based on enzymatic processes taking place in nanofluidic elements is receiving increasing attention by the scientific community. In this work, we describe the construction of novel ultrasensitive enzymatic nanopore biosensors employing "reactive signal amplifiers" as key elements coupled to the transduction mechanism. The proposed framework offers innovative design concepts not only to amplify the detected ionic signal and develop ultrasensitive nanopore-based sensors but also to construct nanofluidic diodes displaying specific chemo-reversible rectification properties. The integrated approach is demonstrated by electrostatically assembling poly(allylamine) on the anionic pore walls followed by the assembly of urease. We show that the cationic weak polyelectrolyte acts as a "reactive signal amplifier" in the presence of local pH changes induced by the enzymatic reaction. These bioinduced variations in proton concentration ultimately alter the protonation degree of the polyamine resulting in amplifiable, controlled, and reproducible changes in the surface charge of the pore walls, and consequently on the generated ionic signals. The "iontronic" response of the as-obtained devices is fully reversible, and nanopores are reused and assayed with different urea concentrations, thus ensuring reliable design. The limit of detection (LOD) was 1 nM. To the best of our knowledge, this value is the lowest LOD reported to date for enzymatic urea detection. In this context, we envision that this approach based on the use of "reactive signal amplifiers" into solid-state nanochannels will provide new alternatives for the molecular design of highly sensitive nanopore biosensors as well as (bio)chemically addressable nanofluidic elements. Fil: Perez Mitta, Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Peinetti, Ana Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Cortez, María Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Toimil Molares, María Eugenia. Gsi Helmholtzzentrum Für Schwerionenforschung; Alemania Fil: Trautmann, Christina. Gsi Helmholtzzentrum Für Schwerionenforschung; Alemania Fil: Azzaroni, Omar. Universitat Technische Darmstadt; Alemania

Surface enhanced solid-state NMR by dynamic nuclear polarization (DNP SENS) enables the characterization of the inner-pore surface functionalization of porous etched ion-track membranes exhibiting low specific surface areas compared to typical SBA- or MCM-type mesoporous silica materials. The membranes were conformally coated with a 5 nm thin SiO2 layer by atomic layer deposition. This layer was subsequently modified by aminopropyl silane linkers that allow further functionalization via the terminal amine group. The results evidence that in principle DNP SENS is a capable tool to analyze more complex porous systems, e.g. bioinspired functional etched ion-track membranes down to the molecular level. These results are relevant also for single nanopore systems, for which a direct analysis of the channel surface functionalization is not feasible by classical characterization methods. The applicability of DNP SENS to complex porous systems requires the optimization of the sample preparation and measurement parameters.

Biomimetic solid-state nanochannels enable new modalities for biosensing. In the last decade, these nanofluidic architectures have been widely studied due to their rapid and sensitive detection capabilities. Developing nanofluidic sensors with great ability to sense ions, small biomolecules, and biological macromolecules requires the combination of versatile surface modification strategies with reliable nanofabrication techniques. Solid-state nanochannels display unique ion transport properties and appealing effects arise when their inner surfaces are charged and the confinement length scale is comparable to the range of the electrostatic interactions in solution. In this context, the integration of molecular recognition elements into the nanochannels yields novel nanofluidic elements with tailored sensoric functions. This review describes recent advances in solid-state nanochannel-based (bio)chemical sensors. The topics covered in this work include sensing principles, nanofabrication techniques and strategies adopted for detecting specific targets, such as ions, small molecules, proteins or nucleic acids, among others. The review highlights several exceptionally promising research directions and discusses how the interplay between the interface chemistry, governed by the bio-receptors, and the remarkable ion transport properties of nanochannels plays a critical role in the analytical performance of the developed devices. In the end, we also offer our vision of the future prospects of this field of research.

International audience; We report on ultrafast vibrational response of single Au-Ag alloy and Au porous nanowires obtained by the template method. The oscillations of the sample reflectivity are correlated to eigenmodes (EM) confined in the nanowire. Taking advantage of a free standing geometry , we are able to detect few harmonics. Coupling electron microscopy and pump-probe investigations with very high spectral resolution performed on the same wire, we demonstrate that both longitudinal and transverse sound velocity could be obtained for variable Au concentration. Additional quadrupolar mode is also observed and reproduced by finite element simulation. Finally, porous nanowires are investigated.

The design of an electrochemically addressable nanofluidic diode is proposed, which allows tunable and nanofluidic operations via redox gating under electrochemical control. The fabrication process involves the modification of an asymmetric gold-coated solid-state nanopore with a thin layer of a redox polymer, poly(vinylferrocene) (PVFc). The composite nanochannel acts as a gate electrode by changing the electrochemical state and, consequently, the conversion/switching of ferrocene into ferricenium units upon the application of different voltages. It is shown that the electrochemical input accurately controls the surface charge density of the nanochannel walls with a predictable concomitant effect on the rectification properties. PVFc-based nanofluidic devices are able to discriminate the passage of anionic species through the nanochannel in a qualitative and quantitative manner by simply switching the redox potential of the PVFc layer. Experimental data confirmed that a rapid and reversible modulation of the ionic transport regimes can be easily attained by changing the applied potential. This applied potential plays the role of the gate voltage (Vg) in field-effect transistors (FET), so these nanofluidic channels behave as ionic FETs. Depending on the Vg values, the iontronic behavior can be switched between ohmic and diode-like regimes. We believe that this system illustrates the potential of redox-active polymers integrated into nanofluidic devices as plausible, simple, and versatile platforms to create electrochemically addressable nanofluidic devices for multiple applications. Fil: Laucirica, Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Marmisollé, Waldemar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Toimil Molares, María Eugenia. GSI Helmholtzzentrum für Schwerionenforschung; Alemania Fil: Trautmann, Christina. GSI Helmholtzzentrum für Schwerionenforschung; Alemania. Universitat Technische Darmstadt; Alemania Fil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Nanotechnology 32(36), 365401 (2021). doi:10.1088/1361-6528/ac04a3, Published by IOP Publ., Bristol

The Seebeck coefficient and electrical resistance of Bi1−xSbx nanowire arrays electrodeposited in etched ion-track membranes have been investigated as a function of wire diameter (40–750 nm) and composition (0 ≤ x ≤ 1). The experimental data reveal a non-monotonic dependence between thermopower and wire diameter for three different compositions. Thus, the thermopower values decrease with decreasing wire diameter, exhibiting a minimum around ∼60 nm. This non-monotonic dependence of the Seebeck coefficient is attributed to the interplay of surface and bulk states. On the one hand, the metallic properties of the surface states can contribute to decreasing the thermopower of the nanostructure with increasing surface-to-volume ratio. On the other hand, for wires thinner than ∼60 nm, the relative increase of the thermopower can be tentatively attributed to the presence of quantum-size effects on both surface and bulk states. These measurements contribute to a better understanding of the interplay between bulk and surface states in nanostructures, and indicate that the decrease of Seebeck coefficient with decreasing diameter caused by the presence of surfaces states can possibly be overcome for even thinner nanowires.

Because of its extended surface area porous gold is of potential interest for surface-enhanced spectroscopy methods. Optical properties of porous and smooth gold nanowires of similar diameter are analyzed with infrared spectroscopy and modeled with finite-difference time-domain simulations. By electrochemical deposition in ion-track etched polymer smooth gold and gold–silver alloy nanowires are synthesized. Porous gold nanowires are subsequently obtained by dealloying. The porosity clearly affects important plasmonic characteristics, resulting in a strong redshift of the resonant wavelength, and significant line broadening, which can be convincingly explained by effective Drude parameters related to a lowered average electron density and a higher electron scattering in the porous gold, respectively. Finally, the sensing performance of porous wires is tested by surface-enhanced infrared absorption. The measurements show a similar vibrational signal contrast for smooth and porous wires. This is explained by simulations which reveal that the nanowire near-field modeled with bulk gold data is higher and thus accordingly the vibrational signal is enhanced compared to nanowires modeled with the effective Drude parameters of porous gold. This means that the advantages offered by the larger surface of porous wires are counterbalanced by lower near-field strength.

Asymmetric membranes and asymmetric pores are broad classes of objects, the role of which is steadily growing in academia and industry. During the last two decades, asymmetric (often called “conical”) track-etched nanopores have attracted increasing attention from the scientific community due to their great potential for accomplishing useful functions in nanofluidic devices. A great body of knowledge has been gained on the electrical and electroosmotic properties of track-etched asymmetric nanopores in electrolyte solutions. Less attention has been paid to the pore geometry, and practically no attempts have been made to explore their osmotic and hydraulic properties. The present study fills this gap by examining the interrelations between the electrical, osmotic, hydraulic and structural characteristics of an asymmetrically etched ion-track nanopore. Several consecutive phases of pore evolution are identified. In the last phase, the highly asymmetric membrane resembles a porous 2D material. The temporal dependences of the two counter-fluxes – the diffusional flux of the etchant and the volume flux of stopping media - are elucidated and analyzed in light of their effect on the nanopore configuration. The osmotic reflection coefficients of highly asymmetric pores are estimated under etching conditions and in diluted electrolyte solutions. Our results allow a new level of understanding of the phenomena underlying the development of an ion-track nanopore and pave the way for the controlled fabrication of a variety of nanopores of different shapes using one and the same principle of an asymmetric chemical treatment.

The implementation of metal and semiconductor nanostructures in devices for catalysis, sensing, and energy conversion requires an excellent control on geometry, crystallinity and composition of the individual nanostructures, as well as its successful assembly into 2-D and 3-D architectures. In particular, nanowire ensembles offer important advantages compared to planar films including e.g. larger surface area and surface to volume ratio, and better crystalline quality. Ion-track nanotechnology is a powerful technique to create templates for the controlled synthesis of such 3-D nanowire architectures. Etched ion-track membranes are fabricated in two separate process steps: (i) sequential irradiation of polymer foils from one or various directions with swift heavy ions resulting in the creation of tracks; (ii) converting the ion tracks into nanochannels by selective chemical etching. Channel density and orientation, as well as diameter and geometry are adjusted by the irradiation and etching conditions, respectively. Afterwards, by electrodeposition in the nanochannels and subsequent removal of the polymer template 3-D assemblies of nanowires are synthesized. Since the nanowires adopt the exact shape of the host channel, their diameter can be adjusted between ~15 nm and a few µm, and their length between ~1 and several tens of µm. In this talk, we will discuss the electrochemical deposition of Au1-xAgx, Cu, and Cu2O in interconnected nanochannel networks, the characterization of the resulting 3-D nanowire assemblies, and the investigation of their photoelectrochemical and catalytical properties.

Nanofluidic reverse electrodialysis systems based on track-etched nanochannels are promising devices for new eco-friendly ways of sustainable energy generation. In recent years, several works have been focused on the influence of parameters such as pH, ionic strength, and chemical nature of the electrolyte on the device performance. However, despite the relevance of the geometry on the channel properties, the influence of the nanochannel shape on the performance of energy conversion remains almost unexplored. In this work, we present an experimental study – complemented with Poisson–Nernst–Planck simulations – that describes how the shape of the nanochannels strongly affects the energy conversion performance of single bullet-shaped nanochannels created on PET foils by the ion-track-etching method. To test optimal parameters for energy conversion and selectivity, the performance was investigated by varying the channel effective diameter as well as the pH and the electrolyte gradient. With a maximum output power of 80 pW, this system reveals the best value reported for a bare single track-etched nanochannel. Therefore, this work experimentally demonstrates that it is possible to obtain high power output by means of a careful choice of channel geometry and etching conditions, in addition to other experimental parameters such as pH and electrolyte gradient. We believe that these results offer a promising framework to explore new design concepts in nanofluidic osmotic power generators., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

The size of ion tracks and hillocks produced during heavy ion irradiation of Y3Fe5O12 is analyzed by transmission electron microscopy. The cross sections of hillocks and ion tracks produced by ions with electronic stopping power Se in the range of 20–35 keV/nm are found to be comparable. In this range, the characteristic dimensions of the hillocks (both cross section and height) increase as a function of Se. The data show that there is a correlation between hillock height and hillock cross section, which is linked to the relation between lifetime of the melt along the ion trajectory and the maximum molten area. In addition, the results clearly show that the size of the hillocks produced by low velocity ions is larger than those produced by high velocity ions of the same Se, due to the so-called velocity effect.

International audience; We report on the magneto-transport properties of individual Bi2Te3 nanowires with diameters ranging from 25 nm to 120 nm fabricated by electrodeposition in etched ion-track membranes. The metallic behavior of all nanowires is typical for highly-degenerate semiconductors and the weak temperature dependence of the resistivity suggests a weak electron-phonon coupling, as expected for topological surface states with quantum confinement. The diameter dependence of the resistivity further confirms the quasi-ballistic nature of charge carriers, in agreement with the reduction of the number of surface conductance channels in disordered quantum wires with a stronger quantum confinement. Although the bulk conductance is not negligible, both the transport length of bulk carriers and their electrostatic screening length remain shorter than the nanowire diameter, probably leading to a small contribution to the resistivity change. Quantum transport measurements give further evidence of finite-size effects, as shown by the weak anti-localization correction to the conductance, below 15K, and reveal the coexistence of surface Aharonov-Bohm oscillations and bulk universal conductance fluctuations, below 5K.

Three-dimensional (3D) assemblies of nanostructures are gaining more and more attention during the recent years as promising systems to increase the integration density in microelectronic devices. Here we present the fabrication of large areas of 3D nanowire networks (NWNWs) of antimony for thermoelectric applications by electrodeposition in etched ion-track membranes. The synthesis parameters have been investigated and optimized to achieve mechanically stable and free-standing NWNWs without a supporting matrix. A cross-plane method for the complete steady state thermoelectric characterization of an embedded nanowire assembly (NWA) is also introduced, which enables the measurements of Seebeck-coefficient, cross-plane thermal conductivity, and electrical resistance of the NWA, and can also be applied to thin films. First results of the thermoelectric properties of Sb NWA are presented.

Metal nanostructures with conical shape, vertical alignment, large ratio of cone height and curvature radius at the apex, controlled cone angle, and single-crystal structure are ideal candidates for enhancing field electron-emission efficiency with additional merits, such as good mechanical and thermal stability. However, fabrication of such nanostructures possessing all these features is challenging. Here, we report on the controlled fabrication of large scale, vertically aligned, and mechanically self-supported single-crystal Cu nanocones with controlled cone angle and enhanced field emission. The Cu nanocones were fabricated by ion-track templates in combination with electrochemical deposition. Their cone angle is controlled in the range from 0.3° to 6.2° by asymmetrically selective etching of the ion tracks and the minimum tip curvature diameter reaches down to 6 nm. The field emission measurements show that the turn-on electric field of the Cu nanocone field emitters can be as low as 1.9 V/μm at current density of 10 μA/cm(2) (a record low value for Cu nanostructures, to the best of our knowledge). The maximum field enhancement factor we measured was as large as 6068, indicating that the Cu nanocones are promising candidates for field emission applications.

Arrays of Bi 1− x Sb x nanowire with various compositions (0 ⩽ x ⩽ 1) are grown in etched ion-track membranes by pulsed electrochemical deposition. Nanowires of diameter from 130 nm down to 18 nm are characterized by means of X-ray diffraction and high-resolution electron microscopy combined with electron diffraction and energy dispersive X-ray analysis. Compared to potentiostatic deposition, the pulsed synthesis method leads to a more uniform growth and higher filling rate of the wires across the entire template. By tuning the deposition parameters, we demonstrate excellent control over the wire composition and crystallographic orientation. The deposition process presented facilitates the development of future nanowire-based thermoelectric sensors, which are expected to exhibit a higher sensitivity and a faster response compared to thin film sensors.

To investigate the physical properties of Bi nanowires and to explore their possible implementation in thermoelectric devices, it is essential to understand their chemical and thermal stability in air both at room and moderate temperatures. In this work, we study the influence of low temperature annealing processes on the morphology and composition of the wires by scanning and transmission electron microscopy and by Raman spectroscopy, revealing the formation of a metal oxide phase. This oxidation process initiates an increase of the nanowires surface roughness at low annealing temperatures, while clear protuberances are formed at 250 °C. Difficulties to electrically contact single Bi nanowires, as well as the high resistance values measured and reported by other groups, are attributed to this oxidation process, which constitutes a clear challenge for the reliable characterization of Bi nanowires and the investigation of their performance.

The fabrication of nanowires by electrodeposition of Au−Ag alloy into the pores of etched ion track polymer membrane is presented. The crystallinity, morphology, and composition of wires with diameters of 85, 45, and 30 nm are investigated by means of X-ray diffraction, high-resolution scanning transmission electron microscopy, and energy-dispersive X-ray analysis. Energy-dispersive X-ray analysis with very high spatial resolution (below 1 nm) reveals the presence of surface enrichment. A Ag-rich layer in Au40Ag60 wires and a Au-rich layer in Au60Ag40 wires with thicknesses between 1 and 4 nm are observed. After dealloying in nitric acid, Ag-rich wires exhibit porous morphologies whereas Au-rich wires remain solid cylinders. The results clearly indicate that the analyzed AuAg alloy nanowires do not consist of homogeneous solid solution, but surface effects before and during the dealloying play an important role for the final morphology of dealloyed nanowires.

Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were performed on these individual nanowires. The influence of a bottom gate was investigated and it was found that surface passivation leads to improved transport properties.

Polycarbonate etched ion-track membranes with about 30 µm long and 50 nm wide cylindrical channels were conformally coated with SiO2 by atomic layer deposition (ALD). The process was performed at 50 °C to avoid thermal damage to the polymer membrane. Analysis of the coated membranes by small angle X-ray scattering (SAXS) reveals a homogeneous, conformal layer of SiO2 in the channels at a deposition rate of 1.7–1.8 Å per ALD cycle. Characterization by infrared and X-ray photoelectron spectroscopy (XPS) confirms the stoichiometric composition of the SiO2 films. Detailed XPS analysis reveals that the mechanism of SiO2 formation is based on subsurface crystal growth. By dissolving the polymer, the silica nanotubes are released from the ion-track membrane. The thickness of the tube wall is well controlled by the ALD process. Because the track-etched channels exhibited diameters in the range of nanometres and lengths in the range of micrometres, cylindrical tubes with an aspect ratio as large as 3000 have been produced.