Search

We use synthesis, electrochemistry, and DFT calculations to show the presence or absence of Cl− modulates binding of PVP to (100) facets, leading to the formation of nanocubes with Cl−, or truncated octahedra without it.

The purpose of this work was to characterize and improve the ability of fused filament fabrication to create anthropomorphic physical phantoms for CT research. Specifically, we sought to develop the ability to create multiple levels of X-ray attenuation with a single material.CT images of 3D printed cylinders with different infill angles and printing patterns were assessed by comparing their 2D noise power spectra to determine the conditions that produced minimal and uniform noise. A backfilling approach in which additional polymer was extruded into an existing 3D printed background layer was developed to create multiple levels of image contrast.A print with nine infill angles and a rectilinear infill pattern was found to have the best uniformity, but the printed objects were not as uniform as a commercial phantom. An HU dynamic range of 600 was achieved by changing the infill percentage from 40% to 100%. The backfilling technique enabled control of up to eight levels of contrast within one object across a range of 200 HU, similar to the range of soft tissue. A contrast detail phantom with six levels of contrast and an anthropomorphic liver phantom with four levels of contrast were printed with a single material.This work improves the uniformity and levels of contrast that can be achieved with fused filament fabrication, thereby enabling researchers to easily create more detailed physical phantoms, including realistic, anthropomorphic textures.

The worldwide proliferation of COVID-19 poses the urgent need for sterilizable and transparent air filters to inhibit virus transmission while retaining ease of communication. Here, we introduce copper nanowires to fabricate transparent and self-sterilizable air filters. Copper nanowire air filter (CNAF) allowed visible light penetration, thereby can exhibit facial expressions, helpful for better communication. CNAF effectively captured particulate matter (PM) by mechanical and electrostatic filtration mechanisms. The temperature of CNAF could be controlled by Joule-heating up to 100 °C with thermal stability. CNAF successfully inhibited the growth of E. coli because of the oligodynamic effect of copper. With heat sterilization, the antibacterial efficiency against G. anodireducens was greatly improved up to 99.3% within 10 min. CNAF showed high reusability with stable filtration efficiency and thermal antibacterial efficacy after five repeated uses. Our result suggests an alternative form of active antimicrobial air filter in preparation for the current and future pandemic situations.

This article describes the synthesis of nanocomposites for the fabrication of printable filaments of interest for additive manufacturing. Boron nitride nanotubes (BNNTs) stand out from several nano...

In this feature article, we provide an account of the Langmuir Lecture delivered by Kristen Fichthorn at the Fall 2020 Virtual Meeting of the American Chemical Society. We discuss how multiscale theory and simulations based on first-principles DFT were useful in uncovering the intertwined influences of kinetics and thermodynamics on the shapes of Ag and Cu cubes and nanowires grown in solution. We discuss how Ag nanocubes can form through PVP-modified deposition kinetics and how the addition of chloride to the synthesis can promote thermodynamic cubic shapes for both Ag and Cu. We discuss kinetic factors contributing to nanowire growth: in the case of Ag, we show that high-aspect-ratio nanowires can form as a consequence of Ag atom surface diffusion on the strained surfaces of Marks-like decahedral seeds. On the other hand, solution-phase chloride enhances Cu nanowire growth due to a synergistic interaction between adsorbed chloride and hexadecylamine (HDA), which leaves the {111} nanowire ends virtually bare while the {100} sides are fully covered with HDA. For each of these topics, a synergy between theory and experiment led to significant progress.

Identical location scanning electron microscopy (IL–SEM) has become an important tool for electrocatalysis research in the past few years. The method allows for the observation of the same site of an electrode, often down to the same nanoparticle, before and after electrochemical treatment. It is presumed that by IL–SEM, alterations in the surface morphology (the growth, shrinkage, or the disappearance of nanosized features) can be detected, and the thus visualized degradation can be linked to changes of the catalytic performance, observed during prolonged electrolyses. In the rare cases where no degradation is seen, IL–SEM may provide comfort that the studied catalyst is ready for up-scaling and can be moved towards industrial applications. However, although it is usually considered a non-invasive technique, the interpretation of IL–SEM measurements may get more complicated. When, for example, IL–SEM is used to study the degradation of surfactant-capped Ag nanocubes employed as electrocatalysts of CO2 electroreduction, nanoparticles subjected to the electron beam during pre-electrolysis imaging may lose some of their catalytic activity due to the under-beam formation of a passive organic contamination layer. Although the entirety of the catalyst obviously degrades, the spot mapped by IL–SEM reflects no or little changes during electrolysis. The aim of this paper is to shed light on an important limitation of IL–SEM: extreme care is necessary when applying this method for catalyst degradation studies, especially in case of nanoparticles with surface-adsorbed capping agents.

Control over the shape of a metal nanostructure grants control over its properties, but the processes that cause solution-phase anisotropic growth of metal nanostructures are not fully understood. ...

Among the electrolyzers under development for CO2 electroreduction at practical reaction rates, gas-fed approaches that use gas diffusion electrodes (GDEs) as cathodes are the most promising. Howev...

The aspect ratio-dependent properties of gold nanorods are used in a variety of applications, but the cause of anisotropic nanorod growth remains unclear. Measurements utilizing single-crystal elec...

Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance.

Room-temperature printing of conductive traces has the potential to facilitate the direct writing of electronic tattoos and other medical devices onto biological tissue, such as human skin. However, in order to achieve sufficient electrical performance, the vast majority of conductive inks require biologically harmful post-processing techniques. In addition, most printed conductive traces will degrade with bending stresses that occur from everyday movement. In this work, water-based inks consisting of high aspect ratio silver nanowires are shown to enable the printing of conductive traces at low temperatures and without harmful post-processing. Moreover, the traces produced from these inks retain high electrical performance, even while undergoing up to 50% bending strain and cyclic bending strain over a thousand bending cycles. This ink has a rapid dry time of less than 2 minutes, which is imperative for applications requiring the direct writing of electronics on sensitive surfaces. Demonstrations of conductive traces printed onto soft, nonplanar materials, including an apple and a human finger, highlight the utility of these new silver nanowire inks. These mechanically robust films are ideally suited for printing directly on biological substrates and may find potential applications in the direct-write printing of electronic tattoos and other biomedical devices.

Metallic nanoparticles of different shape can be used as efficient electrocatalysts for many technologically and environmentally relevant processes, like the electroreduction of CO₂. Intense research is thus targeted at finding the morphology of nanosized features that best suits catalytic needs. In order to control the shape and size distribution of the designed nanoobjects, and to prevent their aggregation, synthesis routes often rely on the use of organic capping agents (surfactants). It is known, however, that these agents tend to remain adsorbed on the surface of the synthesized nanoparticles and may significantly impair their catalytic performance, both in terms of overall yield and of product selectivity. It thus became a standard procedure to apply certain methods (

This article demonstrates a two-step method to 3D print double network hydrogels at room temperature with a low-cost ($300) 3D printer. A first network precursor solution was made 3D printable via extrusion from a nozzle by adding a layered silicate to make it shear-thinning. After printing and UV-curing, objects were soaked in a second network precursor solution and UV-cured again to create interpenetrating networks of poly(2-acrylamido-2-methylpropanesulfonate) and polyacrylamide. By varying the ratio of polyacrylamide to cross-linker, the trade-off between stiffness and maximum elongation of the gel can be tuned to yield a compression strength and elastic modulus of 61.9 and 0.44 MPa, respectively, values that are greater than those reported for bovine cartilage. The maximum compressive (93.5 MPa) and tensile (1.4 MPa) strengths of the gel are twice that of previous 3D printed gels, and the gel does not deform after it is soaked in water. By 3D printing a synthetic meniscus from an X-ray computed tomography image of an anatomical model, we demonstrate the potential to customize hydrogel implants based on 3D images of a patient's anatomy.

Printable electronics has the potential to drastically reduce the environmental and economic costs associated with the production of electronic devices, as well as enable rapid prototyping of circuits and their printing on demand, similar to what 3D printing has done for structural objects. A major barrier to the realization of printable computers that can run programs is the lack of a solution-coatable non-volatile memory with performance metrics comparable to silicon-based devices. Here we demonstrate a non-volatile memory based on Cu-SiO

Physical phantoms with realistic anatomical texture and composition (including contrast media) are of high value and relevance in evaluating the performance of clinical computed tomography (CT) imaging systems. They can offer assessments of image quality in a manner that is more relevant than existing phantoms. The goal of this project was to fabricate anatomically structured 3-D liver texture with added contrast-enhancement. The study used an inkjet printer and customized ink. Patient-informed liver texture with contrast details was first defined computationally and the needed material for each tissue type was estimated for each voxel to produce attenuations from -200 to +300 HU, with subtle 5-20 HU lesions. Volumetric data were printed, one sheet of paper at a time, using “soft tissue” ink based on 200mg/cc sodium bromide (NaBr), and “enhanced tissue” ink based on Isovue-300. The phantom was scanned on a commercial CT system (Siemens SOMATOM Definition Flash) using a clinical protocol. The results show targeted heterogeneity and enhancement as designed with subtle artifacts associated with uneven air contamination. In ongoing work, we plan to use this method to create anatomically and morphologically accurate liver and lung lesions with texture for use in dual energy CT.

This article shows how the chain length of alkylamine capping agents and the corresponding stability of their self-assembled monolayers on a Cu surface determines the growth rate, yield, and dimensions of Cu nanowires produced in a solution-phase synthesis. Of the 10 linear alkylamines that were tested, only those with 12 or more carbon atoms induced growth of nanowires. The length, yield, and growth rate of nanowires were larger for shorter alkylamines. As the Cu nanowire growth rates were up to 1050 times smaller than the calculated diffusion-limited growth rates—and the alkylamine chain length had no significant effect on the in situ generation of the reducing agent—we conclude the rate of alkylamine-mediated Cu nanowire growth is limited by charge transfer. Electrochemical measurements indicate longer alkylamines form more effective passivation layers that greatly decrease the rate at which Cu–alkylamine complexes are reduced onto a Cu surface. Molecular dynamics simulations show that the energy requi...

Interest in flexible, stretchable, and wearable electronics has motivated the development of additive printing to fabricate customizable devices and systems directly onto virtually any surface. However, progress has been limited by the relatively high temperatures (>200 °C) required to sinter metallic inks and time-consuming process steps, many of which require removal of the substrate from the printer for coating, washing, or sintering. In this work, we addressed these challenges and demonstrate carbon nanotube thin-film transistors (CNT-TFTs) that are fabricated by aerosol jet printing with the substrate never leaving the printer. The full in-place printing approach, from first step to last, used a maximum process temperature of only 80 °C on the printer platen. Silver nanowire (Ag NW) ink was found to be most viable for low-temperature, in-place sintering while still yielding good electrical interfaces to the CNT thin-film channels. These aerosol-jet printed Ag NW films were conductive immediately afte...

Materials that retain a high conductivity under strain are essential for wearable electronics. This article describes a conductive, stretchable composite consisting of a Cu–Ag core–shell nanowire felt infiltrated with a silicone elastomer. This composite exhibits a retention of conductivity under strain that is superior to any composite with a conductivity greater than 1000 S cm–1. This work also shows how the mechanical properties, conductivity, and deformation mechanism of the composite changes as a function of the stiffness of the silicone matrix. The retention of conductivity under strain was found to decrease as the Young’s modulus of the matrix increased. This was attributed to void formation as a result of debonding between the nanowire felt and the elastomer. The nanowire composite was also patterned to create serpentine circuits with a stretchability of 300%.

This work examines the use of dual-material fused filament fabrication for 3D printing electronic components and circuits with conductive thermoplastic filaments. The resistivity of traces printed from conductive thermoplastic filaments made with carbon-black, graphene, and copper as conductive fillers was found to be 12, 0.78, and 0.014 Ω cm, respectively, enabling the creation of resistors with values spanning 3 orders of magnitude. The carbon black and graphene filaments were brittle and fractured easily, but the copper-based filament could be bent at least 500 times with little change in its resistance. Impedance measurements made on the thermoplastic filaments demonstrate that the copper-based filament had an impedance similar to a copper PCB trace at frequencies greater than 1 MHz. Dual material 3D printing was used to fabricate a variety of inductors and capacitors with properties that could be predictably tuned by modifying either the geometry of the components, or the materials used to fabricate the components. These resistors, capacitors, and inductors were combined to create a fully 3D printed high-pass filter with properties comparable to its conventional counterparts. The relatively low impedance of the copper-based filament enabled its use for 3D printing of a receiver coil for wireless power transfer. We also demonstrate the ability to embed and connect surface mounted components in 3D printed objects with a low-cost ($1000 in parts), open source dual-material 3D printer. This work thus demonstrates the potential for FFF 3D printing to create complex, three-dimensional circuits composed of either embedded or fully-printed electronic components.

A frequency-diverse computational imaging system synthesized using three-dimensional (3D) printed frequency-diverse metasurface antennas is demonstrated. The 3D fabrication of the antennas is achieved using a combination of PolyLactic Acid (PLA) polymer material and conductive polymer material (Electrifi), circumventing the requirement for expensive and time-consuming conventional fabrication techniques, such as machine milling, photolithography and laser-etching. Using the 3D printed frequency- diverse metasurface antennas, a composite aperture is designed and simulated for imaging in the K-band frequency regime (17.5-26.5 GHz). The frequency-diverse system is capable of imaging by means of a simple frequency-sweep in an-all electronic manner, avoiding mechanical scanning and active circuit components. Using the synthesized system, microwave imaging of objects is achieved at the diffraction limit. It is also demonstrated that the conductivity of the Electrifi polymer material significantly affects the performance of the 3D printed antennas and therefore is a critical factor governing the fidelity of the reconstructed images., Original manuscript as submitted to IET Microwaves, Antennas & Propagation (2017). 17 pages, 8 figures

This article describes a fully printed memory in which a composite of Cu–SiO2 nanowires dispersed in ethylcellulose acts as a resistive switch between printed Cu and Au electrodes. A 16-cell crossbar array of these memristors was printed with an aerosol jet. The memristors exhibited moderate operating voltages (∼3 V), no degradation over 104 switching cycles, write speeds of 3 μs, and extrapolated retention times of 10 years. The low operating voltage enabled the programming of a fully printed 4-bit memristor array with an Arduino. The excellent performance of these fully printed memristors could help enable the creation of fully printed RFID tags and sensors with integrated data storage.

The relatively high temperatures (>200 °C) required to sinter silver nanoparticle inks have limited the development of printed electronic devices on low-cost, heat-sensitive paper and plastic substrates. This article explores the change in morphology and resistivity that occurs upon heating thick films of silver nanowires (of two different lengths; Ag NWs), nanoparticles (Ag NPs), and microflakes (Ag MFs) at temperatures between 70 and 400 °C. After heating at 70 °C, films of long Ag NWs exhibited a resistivity of 1.8 × 10–5 Ω cm, 4000 times more conductive than films made from Ag NPs. This result indicates the resistivity of thick films of silver nanostructures is dominated by the contact resistance between particles before sintering. After sintering at 300 °C, the resistivity of short Ag NWs, long Ag NWs, and Ag NPs converge to a value of (2–3) × 10–5 Ω cm, while films of Ag MFs remain ∼10× less conductive (4.06 × 10–4 Ω cm). Thus, films of long Ag NW films heated at 70 °C are more conductive than Ag NP...

Anthropomorphic phantoms can serve as anatomically structured tools for assessing clinical computed tomography (CT) imaging systems. The aim of this project is to create highly customized 3D inkjet-printed, contrast-enhanced physical liver phantoms for use in improving CT imaging system analysis. The capability of using voxelized print to create physical phantoms with texture was previously presented by our lab. Building on that technology, we show the feasibility of producing iodine enhanced liver phantoms with varying textures, at resolutions higher than clinical CT using inkjetprinting. We use a desktop inkjet-printer, with custom inks to print these paper phantoms. Sodium bromide (NaBr) ink is used to represent unenhanced tissue, and potassium iodide (KI) represents contrast-enhanced tissue. We have shown the feasibility of using 3D inkjet-printing to create unique, contrast-enhanced liver phantoms for use in CT. In the future, we plan to expand our methods and tools to create tissue-equivalent physical phantoms for other anatomical structures in the abdominal region.

Flow-through electrodes such as carbon paper are used in redox flow batteries, water purification, and electroorganic syntheses. This work examines the extent to which reducing the size of the fibers to the nanoscale in a flow-through electrode can increase the productivity of electrochemical processes. A Cu nanowire felt, made from nanowires 45 times smaller than the 10 μm wide fibers in carbon paper, can achieve a productivity 278 times higher than carbon paper for mass-transport-limited reduction of Cu ions. Higher increases in productivity were predicted for the Cu nanowire felt based on the mass-transport-limited current, but Cu ion reduction became charge transfer-limited on Cu nanowire felt at high concentrations and flow rates when the mass-transport-limited current became comparable to the charge transfer-limited current. In comparison, the reaction rate on carbon paper was mass-transport-limited under all concentrations and flow rates because its mass-transport-limited current was much lower than its charge transfer-limited current. Higher volumetric productivities were obtained for the Cu nanowire felt by switching from Cu ion reduction to Alizarin Red S (ARS) reduction, which has a higher reaction rate constant. An electroorganic intramolecular cyclization reaction with Cu nanowire felt achieved a productivity 4.2 times higher than that of carbon paper, although this reaction was also affected by charge transfer kinetics. This work demonstrates that large gains in productivity can be achieved with nanostructured flow-through electrodes, but the potential gains can be limited by the charge transfer kinetics of a reaction.

This Review offers a comprehensive review of the colloidal synthesis, mechanistic understanding, physicochemical properties, and applications of one-dimensional (1D) metal nanostructures. After a brief introduction to the different types of 1D nanostructures, we discuss major concepts and methods typically involved in a colloidal synthesis of 1D metal nanostructures, as well as the current mechanistic understanding of how the nanostructures are formed. We then highlight how experimental studies and computational simulations have expanded our knowledge of how and why 1D metal nanostructures grow. Following specific examples of syntheses for monometallic, multimetallic, and heterostructured systems, we showcase how the unique structure-property relationships of 1D metal nanostructures have enabled a broad spectrum of applications, including sensing, imaging, plasmonics, photonics, display, thermal management, and catalysis. Throughout our discussion, we also offer perspectives with regard to the future directions of development for this class of nanomaterials.

Custom 3D printed physical phantoms are desired for testing the limits of medical imaging, and for providing patientspecific information. This work focuses on the development of low-cost, open source fused filament fabrication for printing of physical phantoms with the structure and contrast of human anatomy in computed tomography (CT) images. Specifically, this paper introduces the concept of using a porous 3D printed layer as a background into which additional material can be printed to control the position-dependent contrast. By using this method, eight levels of contrast were printed with a single material.

The low productivity of organic electrosynthesis limits the adoption of this green methodology for production of organic chemicals. This work examines to what extent reducing the size of the fibers in a flow-through electrode to the nanoscale can increase the productivity of electrosynthesis. A Cu nanowire felt, made from nanowires 45 times smaller than the 10-μm-wide fibers in carbon paper, achieved a productivity 278 times higher than carbon paper for mass transport-limited reduction of Cu ions. For an intramolecular cyclization reaction that was limited by both mass and charge transfer kinetics, the Cu nanowire felt achieved a productivity 4.2 times higher than carbon paper. This work demonstrates large gains in productivity can be achieved with nanostructured flow-through electrodes, but that potential gains can be limited by charge transfer kinetics.

Shape-control is used to tune the properties of metal nanostructures in applications ranging from catalysts to touch screens, but the origins of anisotropic growth of metal nanocrystals in solution are unknown. We show single-crystal electrochemistry can test hypotheses for why nanostructures form and predict conditions for anisotropic growth by quantifying the degree to which different species cause facet-selective metal deposition. Electrochemical measurements show disruption of alkylamine monolayers by chloride ions causes facet-selective Cu deposition. An intermediate range of chloride concentrations maximizes facet-selective Cu deposition on single crystals and produces the highest aspect ratio nanowires in a solution-phase synthesis. DFT calculations similarly show an intermediate monolayer coverage of chloride displaces the alkylamine capping agent from the ends but not the sides of a nanowire, facilitating anisotropic growth.

The ability to 3D print lithium ion batteries (LIBs) in an arbitrary geometry would not only allow the battery form factor to be customized to fit a given product design but also facilitate the use of the battery as a structural component. A major hurdle to achieving this goal is the low ionic conductivity of the polymers used for 3D printing. This article reports the development of anode, cathode, and separator materials that enable 3D printing of complete lithium ion batteries with low cost and widely available fused filament fabrication (FFF) 3D printers. Poly(lactic acid) (PLA) was infused with a mixture of ethyl methyl carbonate, propylene carbonate, and LiClO4 to obtain an ionic conductivity of 0.085 mS cm–1, a value comparable to that of polymer and hybrid electrolytes. Different electrically conductive (Super P, graphene, multiwall carbon nanotubes) and active (lithium titanate, lithium manganese oxide) materials were blended into PLA to determine the relationships among filler loading, conductivi...

Metallic nanoparticles of different shape can be used as efficient electrocatalysts for many technologically and environmentally relevant processes, like the electroreduction of CO2. Intense research is thus targeted at finding the morphology of nanosized features that best suits catalytic needs. In order to control the shape and size distribution of the designed nanoobjects, and to prevent their aggregation, synthesis routes often rely on the use of organic capping agents (surfactants). It is known, however, that these agents tend to remain adsorbed on the surface of the synthesized nanoparticles and may significantly impair their catalytic performance, both in terms of overall yield and of product selectivity. It thus became a standard procedure to apply certain methods (e.g. involving UV-ozone or plasma treatments) for the removal of capping agents from the surface of nanoparticles, before they are used as catalysts. Proper design of the operating procedure of the electrocatalysis process may, however, render such cleaning steps unnecessary. In this paper we use poly-vinylpyrrolidone (PVP) capped Ag nanocubes to demonstrate a mere electrochemical, operando activation method. The proposed method is based on an observed hysteresis of the catalytic yield of CO (the desired product of CO2 electroreduction) as a function of the applied potential. When as-synthesized nanocubes were directly used for CO2 electroreduction, the CO yield was rather low at moderate overpotentials. However, following a potential excursion to more negative potentials, most of the (blocking) PVP was irreversibly removed from the catalyst surface, allowing a significantly higher catalytic yield even under less harsh operating conditions. The described hysteresis of the product distribution is shown to be of transient nature, and following operando activation by a single 'break-in' cycle, a truly efficient catalyst was obtained that retained its stability during long hours of operation.

Fused filament fabrication (FFF) is the most widely available 3D printing technology. Recently, a variety of conductive thermoplastic filaments have become commercially available, allowing printing of electronic structures using the technology. However, the contact interface and conductivity of these filaments after printing remains relatively poor, the latter of which is typically at least four orders of magnitude lower than bulk metal conductors. While several post-processing approaches exist to enhance conductivity, they are either user-intensive, time consuming, or cannot easily be integrated in-line with the rest of the printing process. In this work, we demonstrate that exposing conductive composite thermoplastic films (3D printed or solution-cast) to high-intensity pulsed light increases their conductance by up to two orders of magnitude in a manner that is fast, non-contact, and potentially in-line. This process, referred to as flash ablation metallization (FAM), is found to vaporize the thermoplastic matrix on the top surface of a composite film, leaving behind a metal-dense surface layer. The technique was found to be effective for a variety of commercial and custom-made conductive thermoplastic composites, with the largest response found in Electrifi, a commercial filament consisting of copper particle loading in a biodegradable polyester. 3D-printed circuit boards were constructed with and without FAM exposure, with exposed circuits exhibiting reduced operating voltages as well as improvements in reliability.

With the anticipated effects of global climate change upon us, induced by egregious CO2 emissions, it is imperative to implement technologies to close the carbon cycle. One potential technique to do this is storing the energy from intermittent sources (e.g. solar, wind, hydro) in the form of chemical bonds, such as the electrochemical reduction of CO2. By reducing CO2 to energetically and chemically useful products of CO2 (i.e. CO and C2H4) we can both reduce reliance on fossil fuels and mitigate atmospheric CO2 levels. However, controlling the selectivity towards which particular product is formed and preventing the parasitic hydrogen evolution reaction (HER) is a crucial challenge that must be overcome.1 Exploring fundamental mechanisms and new catalyst materials to overcome this challenge, can be skewed due to the low diffusivity (≈2x10-9 m2/s)2 of CO2 in the liquid phase causing inefficient utilization of catalyst active sites. Unlike the oxygen reduction reaction, use of a rotating disc electrode does not resolve the issue due to the competitive HER reaction. Therefore, it becomes imperative to study physical structure-function relations (e.g. catalyst layer thickness) in a cell that provides ample flux of solely CO2, such as a gas-diffusion electrolyzer (GDE) which greatly increases the diffusivity of CO2 and gas products by enabling transport through gas channels (≈1.6x10-5 m2/s). By filtering nanowires through a gas-diffusion electrode (Figure 1 a-b) we fabricated electrodes of varying thicknesses that were then applied as catalysts in a gas-diffusion electrolyzer (Figure 1c). Results show that even under high CO2 flux conditions there is an interplay between selectivity (Figure 1d), activity (Figure 1e) and catalyst layer thickness. Further exploration of this interplay in commercially relevant electrolyzers can expedite optimized implementation of catalysts in the industrial sector and hopefully aid in solving the global climate crisis at hand. (1) Verma, S.; Kim, B.; Jhong, H.-R. “Molly”; Ma, S.; Kenis, P. J. A. A Gross-Margin Model for Defining Technoeconomic Benchmarks in the Electroreduction of CO2. ChemSusChem 2016, 9 (15), 1972–1979. https://doi.org/10.1002/cssc.201600394. (2) Raciti, D.; Mao, M.; Ha Park, J.; Wang, C. Mass Transfer Effects in CO 2 Reduction on Cu Nanowire Electrocatalysts. Catalysis Science & Technology 2018, 8 (9), 2364–2369. https://doi.org/10.1039/C8CY00372F. Figure 1: Electron microscopy images of Ag nanowires (a) top-down and (b) cross-section, on a gas-diffusion electrode. This electrode is than applied as a CO2 reduction catalyst in a (c) gas-diffusion electrolyzer. The thickness of the Ag nanowire catalyst layer influences both the (d) selectivity and (e) mass activity of the reaction. Figure 1

In this work, silver (Ag) nanocubes with different sizes were rapidly synthesized with a modified HCl-based polyol approach by employing carbamide (CO(NH2)2) as the additive or promoter, which could shorten the reaction time from about 25 h to less than 4 h and the method could be confirmed as facile and robust. In the reaction system, the NH3 molecules play the role of aggregating Ag+ and [Ag(NH3)2]+ could gradually release Ag+, which in turn results in formation of a more homogeneous product in a short time (50 min–4 h). Some factors affecting the synthesis including the concentration, reaction time and agitator speed have also been investigated, which could be adjusted to control the size, morphology, purity and uniformity of the Ag nanocubes. A mechanism for the rapid synthesis of the Ag nanocubes was proposed. To overcome the lower repeatability of reported methods, we have supplied a robust method to synthesize Ag nanocubes and this procedure may provide a useful guide for the future synthesis of Ag or other metal nanoparticles. The transmittance properties of the different Ag nanocubes have also been detected, which demonstrated that the transmittance of the Au film coupled with the Ag nanocubes is very sensitive to not only the size of the Ag nanocubes but also the thickness of the polyelectrolyte molecular spacer layers.

Printable electronics has the potential to drastically reduce the environmental and economic costs associated with the production of electronic devices, as well as enable rapid prototyping of circuits and their printing on demand, similar to what 3D printing has done for structural objects. A major barrier to the realization of printable computers that can run programs is the lack of a solution-coatable non-volatile memory with performance metrics comparable to silicon-based devices. Here we demonstrate a non-volatile memory based on Cu-SiO2 core-shell nanowires that can be printed from solution and exhibits on-off ratios of 106, switching speeds of 50 ns, a low operating voltage of 2 V, and operates for at least 104 cycles without failure. Each of these metrics is similar to or better than Flash memory (the write speed is 20 times faster than Flash). Memory architectures based on the individual memory cells demonstrated here could enable the printing of the more complex, embedded computing devices that are expected to make up an internet of things.

This article describes a room-temperature solution-phase process for the synthesis of copper–silver (Cu–Ag), copper–gold (Cu–Au), and copper–platinum (Cu–Pt) core–shell nanowires (NWs) in which ascorbic acid removes the passivating copper oxide coating from the Cu NWs and reduces noble metal ions onto the Cu NWs while preventing galvanic replacement. Cu–Ag NWs are conductive as printed, and the resulting NW films exhibit optoelectronic properties equivalent to films of Ag NWs with a similar aspect ratio. Unlike Cu NWs, Cu–Ag NWs were resistant to oxidation in dry air at 160 °C and under humid conditions (85% RH) at 85 °C for 24 h.

The repair of a cartilage lesion with a hydrogel requires a method for long-term fixation of the hydrogel in the defect site. Attachment of a hydrogel to a base that allows for integration with bone can enable long-term fixation of the hydrogel, but current methods of forming bonds to hydrogels have less than a tenth of the shear strength of the osteochondral junction. This communication describes a new method, nanofiber-enhanced sticking (NEST), for bonding a hydrogel to a base with an adhesive shear strength three times larger than the state-of-the-art. An example of NEST is described in which a nanofibrous bacterial cellulose sheet is bonded to a porous base with a hydroxyapatite-forming cement followed by infiltration of the nanofibrous sheet with hydrogel-forming polymeric materials. This approach creates a mineralized nanofiber bond that mimics the structure of the osteochondral junction, in which collagen nanofibers extend from cartilage into a mineralized region that anchors cartilage to bone.

Flexible transparent conductors made from networks of metallic nanowires are a potential replacement for conventional, non-flexible, and transparent conducting materials such as indium tin oxide. Cu nanowires are particularly interesting as cost-effective alternatives to Ag nanowires—the most investigated metallic nanowire to date. To optimize the conductivity of Cu nanowire networks, the resistance contributions from the material and nanowire junctions must be independently known. In this paper, we report the resistivity values (ρ) of individual solution-grown Cu nanowires ⟨ρ⟩ = 20.1 ± 1.3 nΩ m and the junction resistance (Rjxn) between two overlapping Cu nanowires ⟨Rjxn⟩ = 205.7 ± 57.7 Ω. These electrical data are incorporated into an electro-optical model that generates analogs for Cu nanowire networks, which accurately predict without the use of fitting factors the optical transmittance and sheet resistance of the transparent electrode. The model's predictions are validated using experimental data from the literature of Cu nanowire networks composed of a wide range of aspect ratios (nanowire length/diameter). The separation of the material resistance and the junction resistance allows the effectiveness of post-deposition processing methods to be evaluated, aiding research and industry groups in adopting a materials-by-design approach.

Since about 20 years ago, researchers have developed a variety of syntheses to control the morphology of metal nanostructures grown in solution.1 Control over nanostructure morphology has enabled the optimization of their properties for applications including electrocatalysis, solution-coatable transparent conducting films, conductive composites and plasmonic biosensors.1 To explain how anisotropic nanostructures can grow from metals with symmetric cubic crystal structures, researchers have often invoked the capping agent hypothesis, which proposes that the organic additives added to nanostructure syntheses are facet-selective in that they block atomic addition to certain facets but not others. However, direct evidence of such facet-selective blocking by organic additives has been lacking. This talk will discuss efforts to use electrochemical measurements on single crystals to test the capping agent hypothesis. For a copper nanowire synthesis in which ethylenediamine was thought to act as a capping agent for {100} facets, single crystal measurements showed it in fact acted as a facet-selective promoter of Cu nanowire growth by keeping the {111} facets on the ends of a nanowire relatively free of surface oxidation.2 In another synthesis in which hexadecylamine is thought to serve as a capping agent for {100} facets, single crystal measurements showed that in fact hexadecylamine passivates both Cu(111) and Cu(100) equally.3 The presence of chloride ions in the synthesis selectively disrupts the alkylamine monolayer on the {111} facets on the ends of the nanowires, enabling anisotropic growth. Addition of iodide ions to the same copper nanowire synthesis results in the formation of Cu microplates instead of nanowires. Single-crystal electrochemistry confirmed that a 75 micromolar concentration of iodide resulted in passivation of {111} facets on the top and bottom surface of microplates due to the displacement of chloride by iodide. At the same time, iodide activated the {100} facets on the sides of the microplates by disrupting the hexadecylamine monolayer on those facets. Results from density functional theory calculations indicate the stronger binding affinity of iodide causes it to displace both chloride and the hexadecylamine monolayer from copper surfaces. The binding of iodide to copper leads to a lower surface energy for {111} facets than {100} facets, resulting in the preferential atomic addition of Cu to the {100} facets on the sides of microplates. These examples illustrate that organic additives do not always act as facet-selective capping agents, and that halide ions can play a dominant in driving the anisotropic growth of copper nanostructures. 1. Huo, D.; Kim, M.J.; Lyu, Z.; Shi, Y.; Wiley, B.J.; Xia, Y. One-Dimensional Metal Nanostructures: From Colloidal Syntheses to Applications. Chem. Rev., 2019, 119, 8972-9073. 2. Kim, M.J.; Flowers, P.F.; Stewart, I.E.; Ye, S.; Baek, S.; Kim, J.J.; Wiley, B.J. Ethylenediamine Promotes Cu Nanowire Growth by Inhibiting Oxidation of Cu (111). J. Am. Chem. Soc. 2017, 39, 277-284. 3. Kim, M.J.; Alvarez, S.; Chen, Z.; Fichthorn, K.A.; Wiley, B.J. Single-Crystal Electrochemistry Reveals Why Metal Nanowires Grow. J. Am. Chem. Soc., 2018, 140, 14740-14746.

Anthropomorphic breast phantoms mimic patient anatomy in order to evaluate clinical mammography and digital breast tomosynthesis system performance. Our goal is to create a modular phantom with an anthropomorphic region to allow for improved lesion and calcification detection as well as a uniform region to evaluate standard quality control (QC) metrics. Previous versions of this phantom used commercial photopolymer inkjet three-dimensional printers to recreate breast anatomy using four surfaces that were fabricated with commercial materials spanning only a limited breast density range of 36% to 64%. We use modified printers to create voxelized, dithered breast phantoms with continuous gradations between glandular and adipose tissues. Moreover, the new phantom replicates the low-end density (representing adipose tissue) using third party material, Jf Flexible, and increases the high-end density to the density of glandular tissue and beyond by either doping Jf Flexible with salts and nanoparticles or using a new commercial resin, VeroPureWhite. An insert design is utilized to add masses, calcifications, and iodinated objects into the phantom for increased utility. The uniform chest wall region provides a space for traditional QC objects such as line pair patterns for measuring resolution and scale bars for measuring printer linearity. Incorporating these distinct design modules enables us to create an improved, complete breast phantom to better evaluate clinical mammography systems for lesion and calcification detection and standard QC performance evaluation.