Unusually small electrical resistance of three-dimensional nanoporous gold in external magnetic fields.
TL;DR: It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be approximately 14 nm.
Abstract: We report the electric conductivity of three-dimensional (3D) nanoporous gold at low temperatures and in strong magnetic fields. It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be approximately 14 nm. This study underscores the importance of 3D topology of a nanostructure on electronic transport properties and has implications in manipulating electron transport by tailoring 3D nanostructures.
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TL;DR: It is shown that hybrid structures made of nanoporous gold and nanocrystalline MnO(2) have enhanced conductivity, resulting in a specific capacitance of the constituent MnO (2) (~1,145 F g(-1)) that is close to the theoretical value.
Abstract: Electrochemical supercapacitors can deliver high levels of electrical power and offer long operating lifetimes, but their energy storage density is too low for many important applications. Pseudocapacitive transition-metal oxides such as MnO(2) could be used to make electrodes in such supercapacitors, because they are predicted to have a high capacitance for storing electrical charge while also being inexpensive and not harmful to the environment. However, the poor conductivity of MnO(2) (10(-5)-10(-6) S cm(-1)) limits the charge/discharge rate for high-power applications. Here, we show that hybrid structures made of nanoporous gold and nanocrystalline MnO(2) have enhanced conductivity, resulting in a specific capacitance of the constituent MnO(2) (~1,145 F g(-1)) that is close to the theoretical value. The nanoporous gold allows electron transport through the MnO(2), and facilitates fast ion diffusion between the MnO(2) and the electrolytes while also acting as a double-layer capacitor. The high specific capacitances and charge/discharge rates offered by such hybrid structures make them promising candidates as electrodes in supercapacitors, combining high-energy storage densities with high levels of power delivery.
1,894 citations
TL;DR: Nanostructuring tungsten diselenide nanoflakes enhances catalytic activity for carbon dioxide conversion to carbon monoxide in an ionic liquid medium and applies this catalyst in a light-harvesting artificial leaf platform that concurrently oxidized water in the absence of any external potential.
Abstract: Conversion of carbon dioxide (CO2) into fuels is an attractive solution to many energy and environmental challenges. However, the chemical inertness of CO2 renders many electrochemical and photochemical conversion processes inefficient. We report a transition metal dichalcogenide nanoarchitecture for catalytic electrochemical CO2 conversion to carbon monoxide (CO) in an ionic liquid. We found that tungsten diselenide nanoflakes show a current density of 18.95 milliamperes per square centimeter, CO faradaic efficiency of 24%, and CO formation turnover frequency of 0.28 per second at a low overpotential of 54 millivolts. We also applied this catalyst in a light-harvesting artificial leaf platform that concurrently oxidized water in the absence of any external potential.
703 citations
TL;DR: In this article, the microstructure, catalytic, and optical properties of nanoporous gold (NPG) have been discussed, with advanced electron microscopy, three-dimensional tomographic reconstructions of NPG have been realized that yield quantitative characterizations of key morphological parameters involved in the intricate structure.
Abstract: Nanoporous metals (NPMs) made by dealloying represent a class of functional materials with the unique structural properties of mechanical rigidity, electrical conductivity, and high corrosion resistance. They also possess a porous network structure with feature dimensions tunable within a wide range from a few nanometers to several microns. Coupled with a rich surface chemistry for further functionalization, NPMs have great potential for applications in heterogeneous catalysis, electrocatalysis, fuel cell technologies, biomolecular sensing, surface-enhanced Raman scattering (SERS), and plasmonics. This article summarizes recent advances in some of these areas and, in particular, we focus on the discussion of microstructure, catalytic, and optical properties of nanoporous gold (NPG). With advanced electron microscopy, three-dimensional tomographic reconstructions of NPG have been realized that yield quantitative characterizations of key morphological parameters involved in the intricate structure. Catalytic and electrocatalytic investigations demonstrate that bare NPG is already catalytically active for many important reactions such as CO and glucose oxidation. Surface functionalization with other metals, such as Pt, produces very efficient electrocatalysts, which have been used as promising fuel cell electrode materials with very low precious metal loading. Additionally, NPG and related materials possess outstanding optical properties in plasmonics and SERS. They hold promise to act as highly active, stable, and economically affordable substrates in high-performance instrumentation applications for chemical inspection and biomolecular diagnostics. Finally, we conclude with some perspectives that appear to warrant future investigation.
370 citations
TL;DR: The "edge-free" monolayer MoS2 films supported by 3D nanoporous gold show high catalytic activities towards hydrogen evolution reaction (HER), originating from large out-of-plane strains that are geometrically required to manage the 3D curvature of bicontinuous nanoporosity.
Abstract: The "edge-free" monolayer MoS2 films supported by 3D nanoporous gold show high catalytic activities towards hydrogen evolution reaction (HER), originating from large out-of-plane strains that are geometrically required to manage the 3D curvature of bicontinuous nanoporosity. The large lattice bending leads to local semiconductor-to-metal transition of 2H MoS2 and the formation of catalytically active sites for HER.
293 citations
TL;DR: Flexible and self-supported microelectrodes with a seamless solid/nanoporous gold/cobalt oxide hybrid structure for electrochemical nonenzymatic glucose biosensors exhibit multi-linear detection ranges with ultrahigh sensitivities at a low potential.
Abstract: Tremendous demands for electrochemical biosensors with high sensitivity and reliability, fast response and excellent selectivity have stimulated intensive research on developing versatile materials with ultrahigh electrocatalytic activity. Here we report flexible and self-supported microelectrodes with a seamless solid/nanoporous gold/cobalt oxide hybrid structure for electrochemical nonenzymatic glucose biosensors. As a result of synergistic electrocatalytic activity of the gold skeleton and cobalt oxide nanoparticles towards glucose oxidation, amperometric glucose biosensors based on the hybrid microelectrodes exhibit multi-linear detection ranges with ultrahigh sensitivities at a low potential of 0.26 V (versus Ag/AgCl). The sensitivity up to 12.5 mA mM⁻¹ cm⁻² with a short response time of less than 1 s gives rise to ultralow detection limit of 5 nM. The outstanding performance originates from a novel nanoarchitecture in which the cobalt oxide nanoparticles are incorporated into pore channels of the seamless solid/nanoporous Au microwires, providing excellent electronic/ionic conductivity and mass transport for the enhanced electrocatalysis.
267 citations
References
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TL;DR: This work ascribes this giant magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecularbeam epitaxy to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.
Abstract: We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecularbeam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with ${t}_{\mathrm{Cr}}=9$ \AA{}, at $T=4.2$ K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.
7,993 citations
TL;DR: In this paper, it was shown that the conductance of disordered electronic systems depends on their length scale in a universal manner, and asymptotic forms for the scaling function were obtained for both two-dimensional and three-dimensional systems.
Abstract: Arguments are presented that the $T=0$ conductance $G$ of a disordered electronic system depends on its length scale $L$ in a universal manner. Asymptotic forms are obtained for the scaling function $\ensuremath{\beta}(G)=\frac{d\mathrm{ln}G}{d\mathrm{ln}L}$, valid for both $G\ensuremath{\ll}{G}_{c}\ensuremath{\simeq}\frac{{e}^{2}}{\ensuremath{\hbar}}$ and $G\ensuremath{\gg}{G}_{c}$. In three dimensions, ${G}_{c}$ is an unstable fixed point. In two dimensions, there is no true metallic behavior; the conductance crosses over smoothly from logarithmic or slower to exponential decrease with $L$.
4,466 citations
TL;DR: In this article, recommended values for the electrical resistivity as a function of temperature from the cryogenic region to well beyond the melting point are given for bulk pure copper, gold, palladium, and silver.
Abstract: In this work, recommended values for the electrical resistivity as a function of temperature from the cryogenic region to well beyond the melting point are given for bulk pure copper, gold, palladium, and silver. In addition to the total electrical resistivity values for the solid state, intrinsic electrical resistivity values are presented from cryogenic temperatures to the melting point. The values are corrected for the change in geometry due to thermal expansion. The recommendations are based on theoretical considerations and on the experimental data found in the open literature. That available experimental data together with information pertaining to the specimen characterization and measurement conditions are included in this work. The methods of data evaluation and other considerations used in arriving at the recommendations are described. For the solid state, an interpolation scheme is given to aid in the determination of values between those supplied in the tables; for the liquid state, equations ...
831 citations
TL;DR: The observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time suggests the possibility of modifying superconductivity and other physical properties of a thin film by exploiting well-controlled and thickness-dependent quantum size effects.
Abstract: We have fabricated ultrathin lead films on silicon substrates with atomic-scale control of the thickness over a macroscopic area. We observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time. This oscillating behavior was shown to be a manifestation of the Fabry-Perot interference modes of electron de Broglie waves (quantum well states) in the films, which modulate the electron density of states near the Fermi level and the electron-phonon coupling, which are the two factors that control superconductivity transitions. This result suggests the possibility of modifying superconductivity and other physical properties of a thin film by exploiting well-controlled and thickness-dependent quantum size effects.
473 citations
TL;DR: In this paper, the surface re-arrangement is considered, which leads to the accumulation of gold-rich surface regions, and throws a new light on the ancient craft of depletion gilding.
Abstract: Noble metal alloys commonly undergo selective dissolution during anodic corrosion whereby the less noble component is dissolved preferentially. This is particularly interesting, as it leads to a depletion of the less noble species not only at the surface of the metal but also at an appreciable depth within it, implying that a mass transport of atoms is occurring either through the bulk of the crystal lattice or across the surface to support the continuing dissolution. Experiments in which the micromorphology of silver–gold alloys is observed during such corrosive treatment have shown that surface diffusion of gold plays an important part in this process. As surface silver atoms are dissolved the residual gold atoms reform into gold-rich islands so that fresh silver atoms are continuously exposed to the environment layer by layer. These observations will be described in detail elsewhere1. Here the mechanism of surface re-arrangement is considered, which leads to the accumulation of gold-rich surface regions, and throws a new light on the ancient craft of depletion gilding.
363 citations