Binary Nanowires Research Articles

Template‐ and Surfactant‐Free Room Temperature Synthesis of Pt/C and Pt−Rh/C Nanowires/Nanoparticles for Ethanol Electro‐Oxidation

AbstractThe synthesis of Pt−Rh alloy nanowires (NWs) using straightforward methodologies remains a challenge. Here, carbon‐supported Pt and Pt−Rh nanowire catalysts were synthesised by chemical reduction at room temperature, without using surfactants or templates. The method of synthesis used yielded Pt/C NWs and a mixture of nanowires with some nanoparticles for the Pt−Rh/C catalysts (characterised using XRD, TEM, EDX, XPS, and XAS). The nanoparticles form due to differences in the surface energy and atomic radius between Pt and Rh. The binary NWs are found to be more active towards ethanol oxidation than the commercial Pt/C reference catalyst. Additionally, the Pt−Rh/C NW catalyst displays a specific activity 2.5‐fold higher than the Pt/C NWs and Pt/C reference catalysts after 15 min of chronoamperometric tests (at 0.5 V vs RHE). Thus, the synthesised carbon‐supported Pt NWs and Pt−Rh nanowires‐nanoparticles are promising alternatives for direct ethanol fuel cell anodes.

Surface Segregation as a Factor of the Stability and Instability of Binary Metal Nanowire

Surface segregation in Ni–Cu binary nanowire is studied using an integrated approach that combines atomistic (molecular dynamics) and thermodynamic simulation. It is shown that a tendency toward the spontaneous surface segregation of Cu atoms is a factor that stabilizes bimetallic structure Ni (core)/Cu (shell) and destabilizes structure Cu (core)/Ni (shell).

Understanding the composition of ternary III-V nanowires and axial nanowire heterostructures in nucleation-limited regime

We present a new analytical approach for understanding and tuning the composition of ternary nanowires of III-V semiconductor compounds and interfacial abruptness of axial nanowire heterostructures in nucleation-limited regime of the vapor-liquid-solid growth. Binary nanowires of elemental semiconductors grown with any liquid catalyst present a simple particular case. The solid composition is first obtained as a function of the liquid composition by determining the saddle point of the island formation energy. This relationship is then used to obtain the compositional profiles across axial heterostructures in a kinetic treatment. Several ternary systems are considered including InGaAs, AlGaAs and InAsP. We find a new effect in InGaAs system which is due to strong interactions between solid InAs and GaAs and yields the miscibility gaps. This may help to form atomically sharp axial heterointerfaces in optimized growth recipes. Our results are consistent with earlier models and experimental data on GaAs/AlGaAs/GaAs nanowire heterostructures. Even more importantly, we formulate general routes for compositional design and obtaining sharp interfaces in different binary and ternary solid alloys.

Large scale synthesis of binary composite nanowires in the Mn2O3-SnO2 system with improved charge storage capabilities

Large scale production of electrochemical materials in non-conventional morphologies such as nanowires has been a challenging issue. Besides, functional materials for a given application do not often offer all properties required for ideal performance; therefore, a composite is the most sought remedy. In this paper, we report large scale production of a composite nanowire, viz. Mn2O3-SnO2, and their constituent binary nanowires by a large scale electrospinning pilot plant consisting of 100 needles. Electrochemical characterization of thus produced composite nanowires showed nearly threefold increase in the discharge capacity compared to their single component counterparts: Mn2O3-SnO2 ∼53mAhg−1 (specific capacitance, CS ∼384Fg−1); Mn2O3 ∼18mAhg−1 (CS ∼164Fg−1); and SnO2 ∼14mAhg−1 (CS ∼128Fg−1) at 1Ag−1 in 6M KOH. The EIS studies showed that the characteristic resistances and time of the composite electrode are appreciably lower than their constituents. Owing to the scalability of the synthesis processes and promising capacitive properties achieved would lead the composite material as a competitive low-cost and high-performance supercapacitor electrode.

Static and Dynamic Magnetization of Gradient FeNi Alloy Nanowire.

FeNi binary nanowires with gradient composition are fabricated by the electrodeposition method. The energy dispersive spec-trometer line-sweep results show that the composition changes gradually along the wire axis. The gradient FeNi nanowires exhibit polycrystalline and crystal twinning at different areas along the nanowire axis, with a textured face-centered cubic structure. The static and dynamic magnetization properties are characterized by a hysteresis loop and ferromagnetic reso-nance with pumping frequencies from 12– 40 GHz. The linear dispersion of the pumping frequency vs: the resonance field has been observed with the applied bias field higher than the saturation field, corresponding to the hysteresis loop. The field-sweep linewidths decrease with increasing pumping frequency, and the frequency-sweep linewidths stay nearly constant at the unsaturated region. The linewidth is a Gilbert type at the saturated state, with damping of 0.035 ± 0.003. Compared with the damping of the homogeneous composition FeNi nanowire (a = 0.044 ± 0.005), the gradient FeNi nanowire may have less eddy current damping, which could make it an alternative candidate for spintronics and microstrip antennas.

Can antimonide-based nanowires form wurtzite crystal structure?

The epitaxial growth of antimonide-based nanowires has become an attractive subject due to their interesting properties required for various applications such as long-wavelength IR detectors. The studies conducted on antimonide-based nanowires indicate that they preferentially crystallize in the zinc blende (ZB) crystal structure rather than wurtzite (WZ), which is common in other III-V nanowire materials. Also, with the addition of small amounts of antimony to arsenide- and phosphide-based nanowires grown under conditions otherwise leading to WZ structure, the crystal structure of the resulting ternary nanowires favors the ZB phase. Therefore, the formation of antimonide-based nanowires with the WZ phase presents fundamental challenges and is yet to be explored, but is particularly interesting for understanding the nanowire crystal phase in general. In this study, we examine the formation of Au-seeded InSb and GaSb nanowires under various growth conditions using metalorganic vapor phase epitaxy. We address the possibility of forming other phases than ZB such as WZ and 4H in binary nanowires and demonstrate the controlled formation of WZ InSb nanowires. We further discuss the fundamental aspects of WZ growth in Au-seeded antimonide-based nanowires.

Fabrication of cobalt-nickel binary nanowires in a highly ordered alumina template via AC electrodeposition

Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO.

Resonant frequencies of a binary magnetic nanowire

Binary nanowires (Co${}_{50}$Fe${}_{50}$/Ni${}_{80}$Fe${}_{20}$) that are 260-nm wide, 25-nm thick, and 4-mm long are fabricated using ``self-aligned shadow deposition'' lithography. Each wire is separated from the next by a gap of 115 nm. Ferromagnetic resonance experiments performed on the nanowires indicate resonant frequencies associated with the Co${}_{50}$Fe${}_{50}$ and the Ni${}_{80}$Fe${}_{20}$ parts of the nanowires. These frequencies are shifted from those measured in nanowires made from just one material or the other due to exchange and dipolar coupling between the two materials. A semianalytic theory is outlined that correctly predicts the resonant frequencies in the binary stripes at various values of static applied field. This calculation is checked against a micromagnetic simulation, and the agreement between both methods and the experiment is good.

Magnetic CrX and MnX (X = Si, Ge, and As) nanowires: Stability enhancement and linearization

This work on elemental and binary nanowires of Cr and Mn, exploring their non-magnetic, ferromagnetic and anti-ferromagnetic states, shows that alloying increases the stability of binary linear chains in comparison to their elemental counterpart. In addition, it also favors not only the linearization of CrAs and MnAs nanowires but also a better magnetic stability for binary linear chains, in general. Furthermore, it is encouraging to note that, besides being more stable, the alloy nanowires are also endowed with a large magnetic moment. Also, the binary nanowires show more feasibility towards tailoring of magnetic state with stretching, in comparison to elemental nanowires. We note that the cohesive energy of studied nanowires is effectively dictated by the X atoms (X=Si, Ge, and As) whereas their magnetic properties are decided by the magnetic M atoms (M=Cr and Mn). Density of states conveys that hybridization of d-states of M atoms and p-states of X atoms plays an important role in higher stability of binary nanowires. The band structure indicates tuning of optical properties of nanowires, while linear chains of MnAs seem suitable for spintronics.

Ultraviolet Photodetector Based on GaN/AlN Quantum Disks in a Single Nanowire

We report the demonstration of single-nanowire photodetectors relying on carrier generation in GaN/AlN QDiscs. Two nanowire samples containing QDiscs of different thicknesses are analyzed and compared to a reference binary n-i-n GaN nanowire sample. The responsivity of a single wire QDisc detector is as high as 2 x 10(3) A/W at lambda = 300 nm at room temperature. We show that the insertion of an axial heterostructure drastically reduces the dark current with respect to the binary nanowires and enhances the photosensitivity factor (i.e., the ratio between the photocurrent and the dark current) up to 5 x 10(2) for an incoming light intensity of 5 mW/cm(2). Photocurrent spectroscopy allows identification of the spectral contribution related to carriers generated within large QDiscs, which lies below the GaN band gap due to the quantum confined Stark effect.

Structural, thermodynamic and mechanical properties of Zr-based binary nanowires (ZrCu and Zr 2Ni) by molecular dynamics

We present molecular dynamics simulation results of two representative cases of nanowires (NWs) of binary alloys, a glass former (ZrCu) and an alloy that becomes amorphous under chemical substitution of its elements (Zr 2Ni). The simulations were based on semiempirical potential models in analogy to the tight-binding scheme in the second moment approximation. We explored the structural characteristics of NWs of various sizes, and we determined several quantities like melting points, strain–stress curves and Young's modulus. We found that for all NWs, the Zr terminations are energetically favored, while Zr 2Ni NWs adopt rounded cross-sectional shapes and ZrCu, octagonal. From the obtained results, it is established that most of the NW properties differ substantially from those exhibited by their bulk counterparts; e.g., lower melting points and greater yield strengths, while under tensile strain they exhibit clear brittle character. In addition, it is found that their mechanical response to deformation is not very sensitive to the imposed strain rates.