Chirality Transfer in Galvanic Replacement Reactions.

Demand for the transfer of chirality from a pre-engineered nanoparticle to any other metal is of fundamental importance for developing a wide range of chirality-related applications. Herein, we show that binary alloy chiral nanoparticles (CNPs) with an engineerable composition can be formed from metallic CNPs with intrinsic structural chirality serving as sacrificial templates (STs), via a galvanic replacement reaction (GRR). This GRR-mediated chirality transfer is a general phenomenon and results in the formation of Cu-Ag CNPs with solid morphology and mesoporous CNPs made of Ag-Au, Ag-Pt, and Ag-Pd. Our study imposes a new component, i.e., structural chirality, on the GRR. The insights from our study improve our fundamental understanding of the GRR principle and devise a versatile method to generate mesoporous alloy CNPs for developing prominent chirality-related applications in asymmetric catalysis, enantiodifferentiation, enantioseparation, biodetection, and bioimaging.

Modulated Triple-Material Nano-Heterostructures: Where Gold Influenced the Chemical Activity of Silver in Nanocrystals.

For efficient charge separations, multimaterial hetero-nanostructures are being extensively studied as photocatalysts. While materials with one heterojunction are widely established, the chemistry of formation of multijunction heterostructures is not explored. This needs a more sophisticated approach and modulations. To achieve these, a generic multistep seed mediated growth following controlled ion diffusion and ion exchange is reported which successfully leads to triple-material hetero-nanostructures with bimetallic-binary alloy-binary/ternary semiconductors arrangements. Ag2 S nanocrystals are used as primary seeds for obtaining AuAg-AuAgS bimetallic-binary alloyed metal-semiconductor heterostructures via partial reduction of Ag(I) using Au(III) ions. These are again explored as secondary seeds for obtaining a series of triple-materials heterostructures, AuAg-AuAgS-CdS (or ZnS or AgInS2 ), with introduction of different divalent and trivalent ions. Chemistry of each step of the gold ion-induced changes in the rate of diffusion and/or ion exchanges are investigated and the formation mechanism for these nearly monodisperse triple material heterostructures are proposed. Reactions without gold are also performed, and the change in the reaction chemistry and growth mechanism in presence of Au is also discussed.

Fabrication of dendritic PdCu alloy supported on 3D N-doped hollow graphene for efficient ethanol electrooxidation.

Fabricating highly efficient Pd-based nanocatalysts with a well-defined structure is desired for the commercialization of direct ethanol fuel cell (DEFC). Herein, a series of hierarchical three-dimensional N-doped hollow graphene spheres (NHGS) supported dendritic PdCu alloy catalysts PdxCu(d)-NHGS (x: Cu/Pd theoretical molar ratio of 4, 2, and 1) are assembled by one-pot ascorbic acid reduction-immobilization method. Aiming to maximize the Pd utilization and realize the efficient ethanol electrooxidation, this novel electrocatalyst offers potent activity sites and promotes electron and ion kinetics simultaneously. Characterization indicates that the as-obtained Pd4Cu(d) alloy nanoparticles with average sizes of approximately 55 nm are evenly dispersed on the NHGS supporting materials obtained by using the SiO2 nanospheres template strategy. Three catalysts all exhibit enhanced electrocatalytic activity, of which the Pd4Cu(d)-NHGS shows the highest mass current activity (2683 mA mgPd-1), which is 2.59 times of the commercial Pd/C toward ethanol electrooxidation in alkaline medium. Based on the results, we believed that the Pd4Cu(d)-NHGS could exhibit extensive application prospect in alkaline DEFC.

Full Composition Tuning of W1-xNbxSe2 Alloy Nanosheets to Promote the Electrocatalytic Hydrogen Evolution Reaction.

Composition modulation of transition metal dichalcogenides is an effective way to engineer their crystal/electronic structures for expanded applications. Here, fully composition-tuned W1-xNbxSe2 alloy nanosheets were produced via colloidal synthesis. These nanosheets ultimately exhibited a notable transition between WSe2 and NbSe2 hexagonal phases at x = 0.6. As x approaches 0.6, point doping is converted into cluster doping and eventually separated domains of WSe2 and NbSe2. Extensive density functional theory calculations predicted the composition-dependent crystal structures and phase transitions, consistently with the experiments. The electrocatalytic activity for the hydrogen evolution reaction (HER) in acidic electrolyte was significantly enhanced at x = 0.2, which was linked with the d-band center. The Gibbs free energy for the H adsorption at various basal and edge sites supported the enhanced HER performance of the metallic alloy nanosheets. We suggested that the dispersed doping structures of Nb atoms resulted in the best HER performance. Our findings highlight the significance of composition tuning in enhancing the catalytic activity of alloys.

In Situ Observation of Structural and Optical Changes of Phase-Separated Ag-Cu Nanoparticles during a Dewetting Process via Transmission Electron Microscopy.

Metallic nanoparticles with localized surface plasmon resonance have suitable optical properties for various applications such as optical filters, efficient photocatalysts, and high-sensitivity sensors. Phase-separated plasmonic nanoparticles with heterogeneous metastructures exhibit unique resonance features with separate optical field enhancements in each phase and hot electron transfer across the interface. Hence, interface engineering is crucial, particularly for catalyst applications. In this study, we investigated the evolution of the interface at high temperatures during nanoparticle formation using the dewetting method. We selected a Ag-Cu binary alloy system as a representative case and observed the nanoparticles via in situ transmission electron microscopy using a dedicated specimen heating holder. In situ elemental mapping revealed that the initial as-deposited film, which was composed of core-shell structures with Ag cores and Cu shells, converted into phase-separated Janus nanoparticles through marbled structures. A major structural change was observed at approximately 200 °C, which was in agreement with optical measurements. These results confirmed that the optical properties and metastructures of the phase-separated nanoparticles could be tuned by selecting the appropriate temperature and duration of the heat treatment.

Proximity-Effect-Induced Anisotropic Superconductivity in a Monolayer Ni-Pb Binary Alloy.

A proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in a normal metal, offering a promising approach to turn heterogeneous materials into superconductors and develop exceptional quantum phenomena. Here, we have systematically investigated proximity-induced anisotropic superconductivity in a monolayer Ni-Pb binary alloy by combining scanning tunneling microscopy/spectroscopy (STM/STS) with theoretical calculations. By means of high-temperature growth, the (33×33)R30o Ni-Pb surface alloy has been fabricated on Pb(111) and the appearance of a domain boundary as well as a structural phase transition can be deduced from a half-unit-cell lattice displacement. Given the high spatial and energy resolution, tunneling conductance (dI/dU) spectra have resolved the reduced but anisotropic superconducting gap ΔNiPb ≈ 1.0 meV, in stark contrast to the isotropic ΔPb ≈ 1.3 meV. In addition, the higher density of states at the Fermi energy (D(EF)) of the Ni-Pb surface alloy results in an enhancement of coherence peak height. According to the same Tc ≈ 7.1 K with Pb(111) from the temperature-dependent ΔNiPb and the short decay length Ld ≈ 3.55 nm from the spatially monotonic decrease of ΔNiPb, both results are supportive of a proximity-induced superconductivity. Despite a lack of a bulk counterpart, the atomically thick Ni-Pb bimetallic compound opens a pathway to engineer superconducting properties down to the two-dimensional limit, giving rise to the emergence of anisotropic superconductivity via a proximity effect.

Formation enthalpies and dilute heats of HCP-HCP disordered binary alloys: modified ones of embedded atom method potentials.

The formation enthalpies and the dilute heats of HCP-HCP disordered binary alloys were evaluated by employing the improved ones of the modified analytic embedded atom method (EAM) potentials for HCP metals. We calculated the formation enthalpies according to the concentration of alloy elements for 36 kinds of HCP-HCP disordered binary alloys by using the modified ones of embedded atom method potentials for HCP metals proposed by Jin et al. (Appl. Phys. A120, 2015, 189), Johnson's alloy potential model, and Vegard's law. We derived the formulas to calculate the dilute heats of HCP-HCP binary alloys and evaluated the dilute heats for 56 kinds of HCP-HCP disordered binary alloys. The present results of the formation enthalpies and the dilute heats for HCP-HCP binary alloys are basically consistent with the experimental data, the first principle calculations, and the calculations by Miedema theory. Our results agree with the available experimental results better than the modified analytic EAM calculation results.

Investigation on mechanical behaviors of Cu-Ni binary alloy nanopillars: a molecular dynamics study.

Cu-Ni binary alloy has become the attention of scientific world for its potentials in nanodevices. It is indispensable to investigate on the mechanical properties of this material due to lack of previous work done regarding this binary alloy. Molecular dynamics (MD) studies were performed on nanopillar (NP) structures comprised of Cu-Ni binary alloy having an FCC unit cell with Cu atoms selectively replaced by Ni atoms. This selective replacement resulted in a better stress behavior than the randomly replaced alloy structure when both tension and compression load were applied. The effect of crystal orientation, NP dimensions, temperature, and strain rate on the stress-strain curve of Cu-Ni binary alloy NPs was thoroughly investigated under tensile loading. This investigation reveals significant influence of crystal orientation on ultimate strength and flow stress region. Among four different crystal orientations, <111> orientation shows maximum strength behavior under tensile loading, while <110> shows highest strength under compressive load. However, in both cases, i.e. tension and compression, the poorest stress behavior was observed for <001> orientation. Under tensile load, <111>-oriented binary alloy fails due to the formation of Shockley partials followed by formation of complex dislocation network. On the other hand, <110>-oriented binary alloy fails due to the formation of Lomer-Cottrell (LC) lock from the Shockley partials. Total dislocation length is calculated, and its effect on the stress-strain behavior of the Cu-Ni binary alloy is discussed. Highest Young's modulus and yield stress are observed on <111>-oriented binary alloy among other orientations, and these values for <111>-oriented NP was found to decrease with the increment of temperature. If the temperature is increased, yield stress and Young's modulus decrease. The effect of cross section width was also investigated in this study, and it was found that yield stress decreases with the increment of cross section width due to the effect of surface atom fraction. Increasing the strain rate causes the initiation of amorphous structure, resulting in superplastic behavior of the <111>-oriented Cu-Ni binary alloy NP.

Dynamic probing of structural evolution for Co50Ni50 metallic glass during pressurized cooling using atomistic simulation.

In this study, firstly favorable glass-forming composition for the binary Co-Ni alloy is identified as Co50Ni50 based on statistically evaluated thermodynamic parameters such as mixing enthalpy (∆Hmix), mixing entropy (∆Smix), and topological parameter such as atomic size difference (δ). Secondly, molecular dynamics (MD) simulations have been performed to investigate the glass-forming ability (GFA) and cluster evolution during the rapid solidification (7.67 K/ps) of Co50Ni50 under hydrostatic pressure (0, 0.25, 0.50, 1, 1.25, 2, 3, 5 GPa). It has been observed that with increasing pressure, glass transition temperature (Tg) also increases thereby increasing the GFA of Co50Ni50. Moreover, Voronoi cluster analysis reveals that quasi-icosahedral type clusters such as <0281> and <0282>, mixed types of cluster such as <0363>, <0364>, <1254>, and <0372> and crystal type clusters such as <0443> and <0444> have maximum population among the other clusters at different pressures at Co as well as Ni-centered atoms.