Bismuth Nanowires Research Articles

Microwave Signature of Topological Andreev level Crossings in a Bismuth-based Josephson Junction.

Demonstrating the topological protection of Andreev states in Josephson junctions is an experimental challenge. In particular the telltale 4π periodicity expected for the current phase relation has remained elusive, because of fast parity breaking processes. It was predicted that low temperature ac susceptibility measurements could reveal the topological protection of quantum spin Hall edge states by probing their low energy Andreev spectrum at finite frequency. We have performed such a microwave probing of a phase-biased Josephson junction built around a bismuth nanowire, a predicted second order topological insulator, and which was previously shown to host one-dimensional ballistic edge states. We find absorption peaks at the Andreev level crossings, whose temperature and frequency dependencies point to protected topological crossings with an accuracy limited by the electronic temperature of our experiment.

Formation of lattice-dislocated bismuth nanowires on copper foam for enhanced electrocatalytic CO2 reduction at low overpotential

Twisted bismuth nanowire (BiNW) with abundant crystal lattice dislocations is a highly active electrocatalyst for CO2 reduction to formate at low overpotential.

Influence of the Size Reduction on the Thermal Conductivity of Bismuth Nanowires

Influence of the Size Reduction on the Thermal Conductivity of Bismuth Nanowires

Synthesis of bismuth nanowires for thermoelectric applications

The processes of synthesis ordered nanowire arrays of bismuth in anodic alumina template ware developed. The sequence of technological operations for the formation of porous templates for the electrochemical deposition of nanowires was described. Optimum electrochemical conditions of reproducible synthesis uniform nanowire arrays were determined. The microstructure and composition of formed structures was studied. The developed techniques are effective for creating perspective nanostructures used in thermoelectric devices.

ELECTROCHEMICAL PREPARATION OF BISMUTH NANOWIRES USING ION-ETCHED POROUS POLYCARBONATE MEMBRANE

Bismuth as “environmentally friendly” metal represents a promising electrode material for different electrochemical techniques. In this study, we prepared bismuth nanowires by chronoamperometry using ion-etched porous polycarbonate membrane. According to SEM- EDX analysis, obtained bismuth nanowires show uniform growth with a high aspect ratio. Due to its large surface, these nanowires have the potential to greatly improve sensor properties for the detection of a variety of inorganic and organic compounds (pollutants, drugs, etc.). Key words: electrodeposition, bismuth, nanowires, SEM-EDX.

Tuning of the Seebeck Coefficient and the Electrical and Thermal Conductivity of Hybrid Materials Based on Polypyrrole and Bismuth Nanowires.

The growing demand for clean energy catalyzes the development of new devices capable of generating electricity from renewable energy resources. One of the possible approaches focuses on the use of thermoelectric materials (TE), which may utilize waste heat, water, and solar thermal energy to generate electrical power. An improvement of the performance of such devices may be achieved through the development of composites made of an organic matrix filled with nanostructured thermoelectric materials working in a synergetic way. The first step towards such designs requires a better understanding of the fundamental interactions between available materials. In this paper, this matter is investigated and the questions regarding the change of electrical and thermal properties of nanocomposites based on low-conductive polypyrrole enriched with bismuth nanowires of well-defined geometry and morphology is answered. It is clearly demonstrated that the electrical conductivity and the Seebeck coefficient may be tuned either simultaneously or separately within particular Bi NWs content ranges, and that both parameters may be increased at the same time.

Manifestations of Surface States in the Longitudinal Magnetoresistance of an Array of Bi Nanowires

The longitudinal magnetoresistance of the array of parallel-oriented bismuth nanowires each 100 nm in diameter grown by electrochemical deposition in nanopores of an Al2O3 membrane has been studied in magnetic fields up to 14 T and at temperatures down to 0.3 K. The resistance increases with the field and reaches a broad maximum in fields about 10 T. An anomalous increase in the resistance in weak fields is qualitatively consistent with the suppression of the antilocalization correction to the resistance, and the maximum is qualitatively associated with the classical size effect. Near the maximum at temperatures below 0.8 K, manifestations of reproducible magneto-oscillations of the resistance, which are periodic in field, have been detected. The period of these oscillations is close to a value corresponding to the passage of the flux quantum hc/e through the section of a nanowire. The Fourier analysis also confirms that the oscillations are periodic. This result is similar to the manifestation the Aharonov–Bohm effect caused by conducting surface states of Dirac fermions occupying L-valleys of bismuth.

Poly(quercetin)-bismuth nanowires as a new modifier for simultaneous voltammetric determination of dihydroxybenzene isomers and nitrite.

Dihydroxybenzene isomers and nitrite, NO2−, are present in the environment as highly toxic compounds and cause human cancer. In this study, for the first time poly(quercetin) (PQ) was synthesized from the reaction between quercetin (Q) and hydroquinone (HQ) as a linker. Bismuth nanowires (BNWs) were synthesized using a solvothermal technique and then the BNWs and PQ were used for preparation of a novel modified graphite paste electrode (GPE/PQ–BNWs) for simultaneous determination of dihydroxybenzene isomers; HQ, catechol (CC), resorcinol (RS) in the presence of NO2−. The product was characterized using X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The electrochemical response characteristics of the modified GPE toward mix HQ, CC, RS and NO2− were investigated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under the optimum conditions, detection limits of 0.12, 0.2, 0.82 and 4.5 μM were obtained for HQ, CC, RS and NO2−, respectively. Moreover, the GPE/PQ–BNWs were applied to determine HQ, CC, RS and NO2− in water samples with satisfactory results.

Spiral Modes and the Observation of Quantized Conductance in the Surface Bands of Bismuth Nanowires

When electrons are confined in two-dimensional materials, quantum-mechanical transport phenomena and high mobility can be observed. Few demonstrations of these behaviours in surface spin-orbit bands exist. Here, we report the observation of quantized conductance in the surface bands of 50-nm Bi nanowires. With increasing magnetic fields oriented along the wire axis, the wires exhibit a stepwise increase in conductance and oscillatory thermopower, possibly due to an increased number of high-mobility spiral surface modes based on spin-split bands. Surface high mobility is unexpected since bismuth is not a topological insulator and the surface is not suspended but in contact with the bulk. The oscillations enable us to probe the surface structure. We observe that mobility increases dramatically with magnetic fields because, owing to Lorentz forces, spiral modes orbit decreases in diameter pulling the charge carriers away from the surface. Our mobility estimates at high magnetic fields are comparable, within order of magnitude, to the mobility values reported for suspended graphene. Our findings represent a key step in understanding surface spin-orbit band electronic transport.

Quantum size effect in single-crystalline bismuth nanorods

In a metal sample, where at least one of the dimensions is comparable with the de Broglie wavelength of conduction electrons, the quantum size effects (QSE) should be observed. QSEs manifest themselves as non-monotonic dependencies of various material properties as function of relevant dimension. QSE should be particularly noticeable in materials with charge carrier(s) effective mass less than the free electron mass. Bismuth is one of the most suitable semi-metal to observe QSE due to small effective masses and small the Fermi energy. However, bismuth has a high anisotropic energy spectrum. Hence to observe QSE which can be interpreted with reasonable accuracy, it is mandatory to fabricate single-crystal nanostructure with known orientation of crystallographic axes. In this paper several short bismuth nanowires (nanorods) were investigated, and oscillating dependence of electric resistance on effective cross section was found. Theoretical calculations provide a reasonable agreement with experiment. The quantum-size phenomena are important for operation of a wide spectrum of nanolelectronic devices.

Strain-engineered allotrope-like bismuth nanowires for enhanced thermoelectric performance

Allotropy is a fundamental concept that has been frequently studied since the mid-1800s. Although the bulk allotropy of elemental solids is fairly well understood, it remains challenging to reliably produce an allotrope at the nanoscale that has a different crystal structure and accompanies a change in physical properties for specific applications. Here, we demonstrate a "heterostructure" approach to produce allotrope-like bismuth nanowires, where it utilizes the lattice constant difference between bismuth and tellurium in core/shell structure. We find that the resultant strain of [100]-grown Bi nanowires increases the atomic linear density along the c-axis that has been predicted from theoretical considerations, enabling us to establish a design rule for strain-induced allotropic transformation. With our >400-nm-diameter nanowires, we measure a thermoelectric figure of merit ZT of 0.5 at room temperature with reduced thermal conductivity and enhanced Seebeck coefficient, which are primarily a result of the rough interface and the reduced band overlap according to our density-functional calculations.

Thermal conductivity of cold compacted bismuth nanowires

In contrast to their macroscale counterparts, nanostructures may exhibit a higher thermoelectric figure of merit (performance) due to their enhanced Seebeck coefficient and/or reduced thermal conductivity. Nonetheless, practical use of individual nanostructures in larger scale thermoelectric applications may not be feasible. Instead, the use of compressed materials formed from these nanomaterials may offer unique opportunities. This work explores the effects of anisotropy and particle size and shape on the thermal transport behavior in compressed materials formed from bismuth nanowires. In its bulk and nanoscale forms, bismuth and its alloys are attractive candidates as thermoelectric materials. Free standing bismuth nanowires of two different diameters, 250 nm and 20 nm, were synthesized through a vapor deposition process and compressed into pellets. Bismuth microparticles (mean diameter 100 µm) were also compressed to the same pressures for comparison. The thermal conductivity of individual nanowires with 250 nm diameter was measured to be 6.1 ± 1.2 W/m K. The compressed nanowire pellets were found to be nearly thermally isotropic with thermal conductivity of approximately 1 W/m K. The microparticle pellets showed a higher degree of anisotropy as well as higher thermal conductivity. Results indicate that thermal characteristics are a function of pellet porosity, compression pressure, and the presence of an oxide layer on the particle surface. The increase in pressure initially reduces the porosity (from 100 to 500 MPa but further compression to 3000 MPa does not influence porosity) and enhances the thermal conductivity for the microparticle samples. The results also indicate the surface oxide is breached due to compression. Some anisotropy in thermal properties due to particle shape and the direction of compression was also observed.

Enhanced Electrochemical Properties of Bi Nanowires as Anode Materials in Lithium and Sodium Batteries

Background: Bismuth (Bi) has been studied due to its high theoretical gravimetric capacity of 385 mAh g−1, which is as important as gravimetric capacity for the practical application of battery systems in electronic mobile devices. However, there have been limited fundamental explorations on the electrochemical performances of Bi. Furthermore, the mechanism differences for the Bi anodes in lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs) should be further investigated. Keywords: Bismuth nanowires, Bi/C nanocomposites, electrochemistry, Li-ion battery, Na-ion battery

Formation and possible growth mechanism of bismuth nanowires on various substrates

In this work, we report results of a study of bismuth nanowires growth on various substrates, including Fe, Ni, Co, W, Pt, Au thin films on oxidized Si, Si (111), oxidized Si (100), and fused quartz. The nanowires (NW) were prepared by RF diode sputtering of Bi onto a substrate heated to about 200 °C. The structure of the wires was studied by a scanning and transmission electron microscopy. The NWs are monocrystalline up to a length of several micrometers and possess a very thin (less than 2 nm) oxide layer. A major influence of the substrate type on the quantity and the length of the obtained nanowires is observed. Based on the above studies, we propose a possible mechanism of a bismuth nanowire growth.

Ballistic edge states in Bismuth nanowires revealed by SQUID interferometry

The protection against backscattering provided by topology is a striking property. In two-dimensional insulators, a consequence of this topological protection is the ballistic nature of the one-dimensional helical edge states. One demonstration of ballisticity is the quantized Hall conductance. Here we provide another demonstration of ballistic transport, in the way the edge states carry a supercurrent. The system we have investigated is a micrometre-long monocrystalline bismuth nanowire with topological surfaces, that we connect to two superconducting electrodes. We have measured the relation between the Josephson current flowing through the nanowire and the superconducting phase difference at its ends, the current–phase relation. The sharp sawtooth-shaped phase-modulated current–phase relation we find demonstrates that transport occurs selectively along two ballistic edges of the nanowire. In addition, we show that a magnetic field induces 0–π transitions and ϕ0-junction behaviour, providing a way to manipulate the phase of the supercurrent-carrying edge states and generate spin supercurrents.

Fabrication of porous bismuth by electrochemical dealloying of Sn–Bi alloys: From microporous structures to nanowire matrix composites

The fabrication of three-dimensional (3D) porous bismuth by electrochemical dealloying of two-phase Sn–Bi alloys was investigated. The results show that the resulting porous bismuth changes from a microporous structure composed of bismuth microparticles to an aligned nanowire matrix composite as the Bi content in the Sn–Bi master alloy decreases. Single-crystal bismuth nanowires growing in the [110] direction were fabricated by the selective dissolution of the Sn phase from an alloy with ultralow Bi content. The influence of the two states of elemental Bi existing in smelted Sn–Bi alloys during dealloying was systematically analyzed and discussed. This report presents a novel strategy for direct fabrication of bismuth nanowires by electrochemical dealloying.

Electronic structure, lattice dynamics, and thermoelectric properties of bismuth nanowire from first-principles calculation

Abstract

Theoretical modeling of electrical resistivity and Seebeck coefficient of bismuth nanowires by considering carrier mean free path limitation

In this study, the electrical resistivity and Seebeck coefficient of bismuth nanowires, several hundred nanometers in diameter, are calculated using the Boltzmann equation in the relaxation time approximation. The three-dimensional density of states and properties of single-crystalline bulk bismuth, such as carrier density, effective mass, and mobility, are used in the calculation without considering the quantum size effect. The relaxation times of the electrons and holes are calculated using Matthiessen's rule considering the carrier collisions at the wire boundary. The temperature, crystal orientation, and diameter dependence of the electrical resistivity and Seebeck coefficient are investigated. The calculation demonstrates that the electrical resistivity increases gradually with decreasing wire diameter, and the temperature coefficient of the electrical resistivity varies from positive to negative at low temperatures for thin wires with diameters less than approximately 500 nm. The diameter dependence of the electrical resistivity varies with the crystal orientation; the increase along the bisectrix axis is larger than that along the binary and trigonal axes. The temperature dependence of the Seebeck coefficient also strongly depends on the crystal orientation. The absolute value of the negative Seebeck coefficient along the bisectrix axis rapidly decreases with decreasing diameter and even changes sign from negative to positive at low temperatures despite the charge neutrality condition, while the Seebeck coefficients along the binary and trigonal axes do not differ significantly from those of single-crystalline bulk bismuth. We conclude that the thermoelectric properties of bismuth nanowires strongly depend not only on the wire diameter but also on the crystal orientation.

Polymer-mediated metallophilic interactions for gram-scale production, high-yield (∼90%) synthesis of ultrathin bismuth nanowires.

High-yields (∼90%) of ultrathin (<4 nm) bismuth nanowires (Bi UNWs) were obtained by reducing the polymeric strands of oleylamine-bismuth 2-ethylhexanoate complexes formed via metallophilic interactions with the mediation of a copolymer (PVP-HDE).

Continuous-feed nanocasting process for the synthesis of bismuth nanowire composites.

We present a novel, continuous-feed nanocasting procedure for the synthesis of bismuth nanowire structures embedded in the pores of a mesoporous silica template. The immobilization of a bismuth salt inside the silica template from a diluted metal salt solution yields a sufficiently high loading to obtain electrically conducting bulk nanowire composite samples after reduction and sintering the nanocomposite powders. Electrical resistivity measurements of sintered bismuth nanowires embedded in the silica template reveal size-quantization effects.