Ru Nanowires Research Articles

Local Oxidation Induced Amorphization of 1.5‐nm‐Thick Pt–Ru Nanowires Enables Superactive and CO‐Tolerant Hydrogen Oxidation in Alkaline Media

AbstractLow‐dimensional amorphous metallic nanomaterials provide great possibility for creating high‐performance electrocatalysts owing to their conspicuous reacting merits derived from the flexible coordination structures, but remain extremely challenging in synthesis. Herein, this work reports a facile synthesis of carbon‐loaded amorphous 1.5‐nm‐thick Pt–Ru nanowires (NWs) through a local oxidation induced amorphization process. During annealing premade crystalline Pt–Ru NWs/C in air, a local‐oxidation of the oxyphilic Ru generates abundant random Ru–O bonds and disturbs the order bimetallic lattices. The as‐prepared amorphous Pt53Ru47 (a‐Pt53Ru47) NWs/C exhibits an extremely high activity (13.7 A mg−1 at 25 mV overpotential) and an excellent CO‐tolerance for alkaline hydrogen oxidation reaction (HOR) electrocatalysis, drastically outperforming the crystalline counterpart and commercial benchmarks. Mechanism studies indicate the Pt–Ru bimetallic effects as well as the rich disordered “Pt–Ru–O” and/or “Pt–O–Ru” atomic heterojunctions can weaken the *H binding energy and inversely strengthen the *OH adsorption, thus promoting the alkaline HOR kinetics. More uniquely, the small interatomic spaces derived from the disordered bond nets present a H2/*H‐selected permeability, which spatially obstruct the relatively larger CO molecules to poison the internal catalytic sites during HOR. The CO‐shielded internal catalytic sites and the enriched surface *OH jointly upgrade the CO‐tolerance of the a‐Pt53Ru47 NWs/C catalysts.

Experimental and Computational Study of the Orientation Dependence of Single-Crystal Ruthenium Nanowire Stability.

Single-crystal nanowires are of broad interest for applications in nanotechnology. However, such wires are subject to both the Rayleigh-Plateau instability and an ovulation process that are expected to lead to their break up into particle arrays. Single crystal Ru nanowires were fabricated with axes lying along different crystallographic orientations. Wires bound by equilibrium facets along their length did not break up through either a Rayleigh-Plateau or ovulation process, while wires with other orientations broke up through a combination of both. Mechanistic insight is provided using a level-set simulation that accounts for strongly anisotropic surface energies, providing a framework for design of morphologically stable nanostructures.

Electrical resistivity evolution in electrodeposited Ru and Ru-Co nanowires

• Propose a strategy to reduce electrical resistivity and complexity of current interconnect structure in ICs. • Emulate a semiconductor metallization environment employing porous nano-templates. • Design nanoscale Ru and Ru-Co structures by electrodeposition. • Uncover electrical properties of Ru-based nanowires and microstructural evolution. Nanoscale ruthenium (Ru)-based materials are promising replacements for existing multilayered Cu interconnects in integrated circuits. However, it is not easy to apply the results of previously reported studies directly to the electrochemical damascene process because the previous studies have mainly focused on thin films by dry deposition. Here, we report the electrical resistivity and microstructure of electrodeposited Ru nanowires. We estimate that the resistivity value of a 10 nm diameter Ru nanowire to be 71.6 μΩ cm after analyzing the resistivity values of individual nanowires with various diameters. Furthermore, we investigate the electrical properties of Ru x Co 1- x nanowires where x is 0.04–0.99 at.% as possible replacements of the current TaN barrier structures. Over the entire composition range, the resistivity values of alloys are much lower than that of the conventional TaN. Additionally, Ru and Ru-alloy nanowires surrounded by dielectric silica are thermally stable after 450 °C heat treatment. Therefore, the nanoscale Ru and Ru-Co alloys possessing low resistivity values can be candidates for the interconnect and barrier materials, respectively.

Fabrication of junction-free Cu nanowire networks via Ru-catalyzed electroless deposition and their application to transparent conducting electrodes

Over the past few years, metal nanowire networks have attracted attention as an alternative to transparent conducting oxide materials such as indium tin oxide for transparent conducting electrode applications. Recently, electrodeposition of metal on nanoscale template is widely used for formation of metal network. In the present work, junctionless Cu nanowire networks were simply fabricated on a substrate by forming a nanostructured Ru with 80 nm width as a seed layer, followed by direct electroless deposition of Cu. By controlling the density of Ru nanowires or the electroless deposition time, we readily achieve desired transmittance and sheet resistance values ranging from ∼1 kΩ sq−1 at 99% to 9 Ω sq−1 at 89%. After being transferred to flexible substrates, the nanowire networks exhibited no obvious increase in resistance during 8000 cycles of a bending test to a radius of 2.5 mm. The durability was verified by evaluation of its heating performance. The maximum temperature was greater than 180 °C at 3 V and remained constant after three repeated cycles and for 10 min. Transmission electron microscopy and x-ray diffraction studies revealed that the adhesion between the electrolessly deposited Cu and the seed Ru nanowires strongly influenced the durability of the core–shell structured nanowire-based heaters.

Ar/H2/O2‐Controlled Growth Thermodynamics and Kinetics to Create Zero‐, One‐, and Two‐Dimensional Ruthenium Nanocrystals towards Acidic Overall Water Splitting

AbstractA gas controlled formation strategy is developed to synthesize free‐standing 0D Ru nanoparticles, 1D Ru nanowires, and 2D Ru nanosheets through in‐situ regulated growth thermodynamics and kinetics with typical inert, reductive, and oxidative gases (Ar/H2/O2). The growth process of these Ru nanoparticles, nanowires, and nanosheets follow non‐directional growth, shape‐directed nanoparticle attachment, and directional growth mechanisms, respectively. Kinetics studies approve that H2 accelerates the reduction rate of the Ru precursor, while O2 depresses the reduction. The calculation results of the Gibbs surface free energy under different gas coverage further show that small molecules’ gas can effectively regulate the surface state and growth rate. These Ru nanocrystals exhibit excellent acidic water splitting performance. This work has systematically studied the influence of the small molecule gas on the formation process of the Ru nanocrystals, and provides an effective idea for the development and research of high‐performance nanomaterials in the future.

Mechanical integrity of back-end-of-line with Ru nanowires and airgaps

In this study, the mechanical integrity of novel back-end-of-line (BEOL) with ruthenium nanowires and airgaps was investigated using a combination of nano-indentation, delamination tests and finite element modelling. The ruthenium interconnects with and without airgaps were benchmarked against standard dual damascene copper BEOLs. The impact of interconnect aspect ratio, adhesion promotion at the metal-dielectric interfaces, airgap implementation and low-k dielectric selection was investigated. The study demonstrates that ruthenium-airgap interconnects of high aspect ratio 3 with standard adhesion promoting layers at the metal-dielectric interfaces and interlevel dielectric's Young's moduli as low as 12 GPa, can provide a mechanical integrity on a par with dual damascene Cu BEOL.

Enhancing electrochemical nitrogen reduction with Ru nanowiresviathe atomic decoration of Pt

Atomic-Pt-decorated Ru nanowires improve electrocatalytic nitrogen reduction owing to the tensile strain-induced enhancement of N2adsorption and N2H* stabilization.

Surface sites assembled-strategy on Pt-Ru nanowires for accelerated methanol oxidation.

Modifying the surface active sites of Pt-based catalysts at the atomic level is of great significance to enhance the electrooxidation of methanol molecules. Herein, efficient active site assembly strategies are proposed, precisely, aimed at building high-performance electrocatalysts. Serving as proof-of-concept examples, both instances of Pt nanowires surface doping isolated Ru atoms (Ru/Pt NWs) and Ru nanoparticles supported on Pt nanowires (Ru@Pt NWs) are specially designed to optimize the catalytic performance of methanol oxidation reaction (MOR). The specific activity and mass activity of optimal Ru/Pt NWs can reach up to 3.93 mA cm-2 and 568.40 mA mg-1Pt, respectively, which is 1.53/1.94 times that of the Ru@Pt NWs and 2.03/2.59 times that of pure Pt NWs. Detailed studies on mechanism reveal that the Pt-Ru alloy can significantly improve the electron transfer kinetics of MOR, and activate more Pt atoms involved in the Langmuir-Hinshelwood (L-H) pathway compared with Ru@Pt NWs, all of which collectively accelerate the methanol oxidation. This surface engineering strategy via assembling active sites can reveal a promising method in the design of advanced Pt-based catalysts for direct methanol fuel cells.

Ru Nanoframes with an fcc Structure and Enhanced Catalytic Properties.

Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd-Ru core-frame octahedra could be easily converted to Ru octahedral nanoframes of ∼2 nm in thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. The fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.

Improved catalytic performance of encapsulated Ru nanowires for aqueous-phase Fischer–Tropsch synthesis

Ru–PVP nanowires encapsulated in ethane–silica hollow nanospheres could efficiently and steadily catalyze liquid-phase F–T synthesis with higher activity (activity: 6.35 versus 5.96 molCO mol−1Ru h−1) and selectivity towards oxygenate products (41.3 versus 21.6%) than free Ru–PVP.

Highly active Pt–Ru nanowire network catalysts for the methanol oxidation reaction

Platinum–ruthenium alloy nanowire networks (Pt–Ru NWNs) have been successfully synthesized by a surfactant assisted soft template strategy, involving the chemical reduction of platinum and ruthenium complexes using sodium borohydride. These materials are investigated as methanol oxidation reaction (MOR) catalysts for fuel cell applications and were found to display exemplary MOR activity and CO tolerance through cyclic voltammetry (CV) testing. Pt–Ru-NWNs investigated in this work are proposed as promising anode replacements to traditional Pt–Ru catalysts in direct methanol fuel cells.

Synthesis and Characterization of Well Aligned Ru Nanowires and Nanotubes

Arrays of well aligned Ru nanowires and nanotubes were prepared by electrodeposition through porous anodic aluminum oxide membranes. It is shown that Ru nanowires are formed at low cathodic deposition overpotential, while nanotubes are prepared at higher cathodic overpotential. The inner diameter of the nanotube can be controlled by the deposition potential, and it varies from 0 to 70% of the outer diameter as the deposition potential is changed from -0.30 to -0.45 V vs SCE.

Selective Wet-Chemical Etching of the Barrier Layer during Formation of Porous Anodic Aluminum Oxide Template

A porous anodic aluminum oxide (AAO) template with a TiN bottom electrode was fabricated on a substrate. The anodizing process ended up stably with the formation of pillars penetrating the barrier layer, and the pillars were selectively and uniformly removed using standard clean-1 solution . Ru nanowires were fabricated in the AAO nanochannels with an aspect ratio of 10:1 by an atomic layer deposition process using as a precursor and as a reducing agent. The contact between Ru nanowires and a TiN bottom electrode was confirmed by a transmission electron microscope. The current–voltage characteristic of each Ru nanowire through the TiN bottom electrode was resolved by a conductive atomic force microscope, which showed the uniform ohmic behavior of the contact with a resistance of as low as per single Ru nanowire. The stable wet-chemical route to the selective and uniform removal of the barrier layer of the AAO template was applied to devices that require a good electrical connection to nanowires with high aspect ratios, such as sensors, batteries, or optoelectronic devices.

Microelectromechanical system microhotplates for reliability testing of thin films and nanowires

Microelectromechanical system microhotplates fabricated using silicon-on-insulator wafers were designed and fabricated for accelerated lifetime testing of thin films and nanowires. Thin films of Cr∕Ru∕Au, Cr∕Ru, and Ru were examined as well as nanowires of Ru and RuOx. Rapid thermal cycling at a 1kHz pulse frequency was employed for testing the thin films. Nanowires were characterized using 1kHz and 500Hz pulse frequencies. A 40nm layer of sputtered Au deposited on 12nm of sputtered Ru and 8nm of sputtered Cr displayed a sheet resistance of 1.18Ω∕◻ and a lifetime of 267h before failure when cycled with a peak temperature of 692K. Ru thin films with a thickness of 12nm displayed a sheet resistance of 51Ω∕◻ and a lifetime of 10h under the same conditions. Sputtered Ru and RuOx nanowires with thicknesses of 15 and 32nm, respectively, displayed resistivities of 72×10−8 and 320×10−8Ωm. It was found that the cycling frequency did not influence the nanowire lifetimes in air or in N2. Ru nanowires tested in N2 displayed lifetimes of 450min followed by Ru nanowires tested in air with lifetimes of 340min and finally by RuOx nanowires tested in air with lifetimes of 45min. This latter behavior is attributed to a higher surface diffusion in RuOx compared to Ru. An activation energy of 0.29eV was observed for failure of Ru nanowires tested in air conditions. Biased percolating behavior with critical exponents ranging from 0.5 to 0.7 was found to describe the electrical behavior for all the nanowires.

Pt–Ru nanowire arrayed electrodes for nitrite detection

Pt–Ru nanowire arrayed electrodes were successfully synthesized by means of cathodic deposition technique using the membrane–template synthesis route. The desired there-dimensional architecture of Pt–Ru nanowire arrayed electrodes was characterized with scanning electron microscope and X-ray diffraction techniques. It was found that the co-deposition nanowires were freestanding on the substrate with an average diameter of about 30 nm, a nearly 9:1 atomic ratio of Pt to Ru and a face-centered cubic structure. The nanowire arrayed electrodes showed better catalytic ability than glass carbon electrode toward the oxidation of nitrite anions for the facility of electrolyte penetration, the ease of proton exchange/diffusion and the metallic conductivity of Pt–Ru nanowire arrayed electrodes. About 400 mV decreased overpotential and 2.7 fold enhanced voltammetric current were achieved.

Metallic contacts with individual Ru nanowires prepared by electrochemical deposition and the suppression of superconductivity in ultrasmall Ru grains

Nanowires of Ru are a promising candidate for studying the intrinsic behavior of individual one-dimensional superconducting wires. We have prepared Ru nanowires by electrochemical deposition in porous polycarbonate membranes and characterized them structurally by high-resolution transmission electron microscopy and electron diffraction. Ru wires with diameters of 50 and 100nm were found to be polycrystalline, consisting of ultrasmall Ru grains with a typical size of 2nm. Metallic contacts to arrays of Ru nanowire as well as individual wires were made. Electrical transport measurements showed that these wires were metallic, but not superconducting down to 0.3K.

Bimetallic Pt–Ru nanowire network for anode material in a direct-methanol fuel cell

Abstract A new bimetallic nanostructured Pt–Ru material is synthesized in an SBA-15 nanoreactor and compared with commercial Pt–Ru black (Johnson Matthey). Transmission electron microscopic and X-ray diffraction studies of the synthesized material show that, as with a network structure, the Pt–Ru nanowires are interconnected via smaller ones. The catalytic activity (measured in cyclic voltammetry (CV) experiments) for methanol electro-oxidation on the material is lower than that for commercial Pt–Ru black at potentials below 550 mV versus the reversible hydrogen electrode. By contrast, a direct-methanol fuel cell (DMFC) in which the nanostructured material is used as an anode material shows higher performance than with Pt–Ru black, because the network structure leads to an effective mass transfer in the membrane–electrode assembly.