Bismuth Nanowires Research Articles

Electronic and structural properties of rhombohedral [1 1 1] and [1 1 0] oriented ultra-thin bismuth nanowires

Structures and electronic properties of rhombohedral [1 1 1] and [1 1 0] bismuth nanowires are calculated with the use of density functional theory. The formation of an energy band gap from quantum confinement is studied and to improve estimates for the band gap the GW approximation is applied. The [1 1 1] oriented nanowires require surface bonds to be chemically saturated to avoid formation of metallic surface states, whereas the surfaces of the [1 1 0] nanowires do not support metallic surface states. It is found that the onset of quantum confinement in the surface passivated [1 1 1] nanowires occurs at larger critical dimensions than for the [1 1 0] nanowires. For the [1 1 1] oriented nanowires it is predicted that a band gap of ~0.5 eV can be formed at a diameter of approximately 6 nm, whereas for the [1 1 0] oriented nanowires a diameter of approximately 3 nm is required to achieve a similar band gap energy. The GW correction is also applied to estimates of the electron affinity, ionisation potentials and work functions for both orientations of the nanowires for various diameters below 5 nm. The magnitude of the energy band gaps that arise in bismuth at critical dimensions of a few nanometers are of the same order as for conventional bulk semiconductors.

The fabrication and thermal properties of bismuth–aluminum oxide nanothermometers

Bismuth (Bi) nanowires, well controlled in length and diameter, were prepared by using an anodic aluminum oxide (AAO) template-assisted molding injection process with a high cooling rate. A high performance atomic layer deposition (ALD)-capped bismuth–aluminum oxide (Bi–Al2O3) nanothermometer is demonstrated that was fabricated via a facile, low-cost and low-temperature method, including AAO templated-assisted molding injection and low-temperature ALD-capped processes. The thermal behaviors of Bi nanowires and Bi–Al2O3 nanocables were studied by in situ heating transmission electron microscopy. Linear thermal expansion of liquid Bi within native bismuth oxide nanotubes and ALD-capped Bi–Al2O3 nanocables were evaluated from 275 °C to 700 °C and 300 °C to 1000 °C, respectively. The results showed that the ALD-capped Bi–Al2O3 nanocable possesses the highest working temperature, 1000 °C, and the broadest operation window, 300 °C–1000 °C, of a thermal-expanding type nanothermometer. Our innovative approach provides another way of fabricating core–shell nanocables and to further achieve sensing local temperature under an extreme high vacuum environment.

Temperature Dependence of the Resistivity and Seebeck Coefficient of Individual Single-Crystal Bismuth Nanowires of 345-nm and 594-nm Diameters Encased in a Quartz Template

Temperature dependence measurements of resistivity and the Seebeck coefficient were performed using individual bismuth nanowires of 345-nm and 594-nm diameters encased in a quartz template. Each nanowire was confirmed as a single crystal by Laue measurement, and an advanced mean free path model was utilized to explain both temperature dependencies. The model successfully explains the dependence over 100 K, which occurs because the carrier mobility is restricted by boundary scattering at the nanowire surface considering the crystal orientation along the wire length direction, band structure, and isotropic Fermi surface. However, it is difficult to determine the temperature dependence of the resistivity in the low-temperature region, in which a much higher temperature coefficient is indicated, especially at temperatures lower than 50 K. Although we calculated the temperature dependence of the resistivity with the influence of p-type contamination in the nanowire because a positive Seebeck coefficient at low temperatures was observed, an explanation of the resistivity in the low-temperature region has not been developed. Therefore, a hypothesis was introduced in which the hole mobility was not restricted in the nanowire, and the hole mobility was estimated by the mobility ratio from the Seebeck coefficient, the measured resistivity, and the electron mobility using the model. Lastly, the temperature dependence of the resistivity can be explained over the entire temperature region. This result suggests that the scattering mechanism between holes and electrons in the nanowire differs and depends on the crystal orientation in the low-temperature region.

Fabrication of a Nanoscale Electrical Contact on a Bismuth Nanowire Encapsulated in a Quartz Template by Using FIB-SEM

A method to fabricate an electrode on a 110-nm-diameter Bi nanowire, encapsulated in a quartz template, was established using a dual beam instrument equipped with a focused ion beam and a scanning electron microscope. A fabrication method has already been successfully developed to obtain suitable Ohmic contact on both ends of Bi nanowires (several hundred nanometers in diameter) by first polishing the ends of the nanowires, and then depositing titanium/copper thin-films via an ion-plating method. However, with this method, it was difficult to obtain suitable electrodes on Bi nanowires with diameters less than 300 nm. Therefore, in order to understand why it was not possible to establish an electrical contact in small-diameter Bi nanowires, the vertical section of the fabricated electrode and the end of a 110-nm-diameter Bi nanowire were observed using a focused ion beam scanning electron microscope. A vacant area was observed between the end of the nanowire and the titanium thin-film, indicating a possible cause for the electrical contact failure. This implies that the quartz-encapsulated Bi nanowire is selectively removed when it undergoes polishing due to the great difference in hardness between Bi and quartz. A local electrode, which would connect the exposed area of the Bi nanowire and the metal thin-films on the surface of the quartz template, was fabricated by tungsten deposition using an electron beam. After fabrication of the opposite-end electrode by the same method, an electrical connection was successfully confirmed by measuring the voltage between both ends of the metal thin-films with a circuit tester. Ohmic contact was confirmed by measuring the current–voltage characteristics between the fabricated electrodes. As a result, the electrical resistivity and Seebeck coefficient were successfully measured at 300 K.

Local Structural Distortion Induced Uniaxial Negative Thermal Expansion in Nanosized Semimetal Bismuth.

The corrugated layer structure bismuth has been successfully tailored into negative thermal expansion along c axis by size effect. Pair distribution function and extended X-ray absorption fine structure are combined to reveal the local structural distortion for nanosized bismuth. The comprehensive method to identify the local structure of nanomaterials can benefit the regulating and controlling of thermal expansion in nanodivices.

Facile and Efficient Synthesis of Bismuth Nanowires for Improved Photocatalytic Activity.

An aqueous reduction method was reported for the synthesis of bismuth nanowires (Bi NWs) 5-10 nm in diameter and several micrometers in length under the guidance of PVP molecules. The reactions were performed at 80 °C by reducing bismuth chloride with sodium hypophosphite first in acid and then under neutral circumstances. The key to successful preparation of the Bi NWs is regulation of the reduction speed by control of the pH value. The morphology evolution of the samples was also found to have a strong dependence on the reaction parameters, including the introduction amount and molecular weight of PVP molecules. A solid-solution-solid (SSS) mechanism was proposed for the nucleation and growth of Bi NWs in our strategy. The as-prepared Bi NWs exhibit excellent visible-light photocatalytic activities for the degradation of the organic pollutant Rhodamine B (RhB) and colorless bisphenol A (BPA). The good recyclability of the Bi NWs on RhB photodegradation demonstrates the possibility of their practical applications.

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

Temperature-Dependent Electrical Conductance of Bi Nanowires

The single crystal bismuth nanowire arrays grown along [011¯2] with the diameter of 30 nm was synthesized in the pore of anodic aluminum oxide templates through electrodeposition process. The temperature dependent electric conductance of Bi nanowire arrays was measured from 78 K to 320 K. We found that the semimetal-to-semiconductor transition happened around 230 K for 30 nm Bi nanowires oriented along [011¯2] and the electric conductance of the nanowires had a strong temperature dependence.

Synthesis and Characterization of High-Purity Bismuth Nanowires via Seed-Assisted Growth Approach

Nanowires are considered as high-performance thermoelectric materials with large Seebeck coefficients due to quantum confinement and low thermal conductivity because of enhanced boundary scattering of phonons. In this work, a seed-assisted growth method has been developed to synthesize high-purity bismuth nanowires. The bismuth seeds were first synthesized by reducing BiCl3 in the ice water with NaBH4. The high-purity bismuth nanowires about 40–50 nm in diameter and several tens of micrometers in length were then grown on bismuth seeds by reducing NaBiO3 with ethylene glycol. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were employed to characterize the crystal structure, microstructure, and growth direction of the bismuth seeds and nanowires. The effects of temperature, reductant, and bismuth seeds template on the microstructures of the bismuth nanowires were also investigated. The synthesis conditions of bismuth seeds and nanowires were optimized. The selected area electron diffraction pattern confirms that the growth direction of bismuth nanowires is parallel to [\( 11\bar{2}0\)] direction. It was discovered that high-purity bismuth nanowires with high aspect ratio can be synthesized by precisely controlling the temperature to adjust the nucleation rate of the bismuth nuclei, selecting the appropriate reductant to maintain a low nucleation rate, and using bismuth seeds as the template of the epitaxial growth of the bismuth nuclei.

Spontaneous growth of bismuth nanowires on a sputter-deposited thin bismuth film

Thin films of bismuth of thickness 100nm have been deposited onto Si(111) substrates held at 120°C using magnetron sputter deposition. The three-inch magnetrons were operated at DC powers between 30W and 50W to give deposition rates between 0.03 and 0.09nms−1. Examination of the surface of the thin films using scanning electron microscopy revealed nanowires of diameter 80–120nm and length between 3 and 16μm emerging from the film. An investigation of the effect of deposition rate found little influence on the nanowire diameter, but indicated that some longer nanowires could be found on the film deposited at the lowest rate. A 20nm film grown on glass at 110°C shows a nanowire with dimension of around 50nm. Using a relatively higher rate for the first 25nm followed by a lower rate to 100nm produced some very straight and regular nanorods.

Bismuth nanowire thermoelectrics

Here, we review the current progress in the thermoelectrics of bismuth nanowires, the fundamentals of their advantage and limitation over bulk Bi, and their potential use for enhancing thermoelectric performance.

Magnetic field resistant quantum interferences in Josephson junctions based on bismuth nanowires

We investigate proximity-induced superconductivity in micrometer-long bismuth nanowires connected to superconducting electrodes with a high critical field. At low temperature we measure a supercurrent that persists in magnetic fields as high as the critical field of the electrodes (above 11 T). The critical current is also strongly modulated by the magnetic field. In certain samples we find regular, rapid SQUID-like periodic oscillations occurring up to high fields. Other samples exhibit less periodic but full modulations of the critical current on Tesla field scales, with field-caused extinctions of the supercurrent. These findings indicate the existence of low dimensionality, phase coherent, interfering conducting regions through the samples, with a subtle interplay between orbital and spin contributions. We relate these surprising results to the electronic properties of the surface states of bismuth, strong Rashba spin-orbit coupling, large effective $g$ factors, and their effect on the induced pair correlations. In particular, we emphasize the possible contribution of topological edge states of specific facets of the nanowires.

Facile one-step direct electrodeposition of bismuth nanowires on glassy carbon electrode for selective determination of folic acid

In the present work, we have developed a facile one step route to electrodeposition of stabilizer-free bismuth nanowires (BiNWs) on glassy carbon (GC) substrates by using a simple potentiostatic method. Formation of BiNWs on GC substrate was confirmed by field emission scanning electron microscopy (FE-SEM). The growth of BiNWs on the GC substrate was monitored by cyclic voltammetry and found that continuous in-situ generation of hydrogen bubbles during electrodeposition provides a stagnant template for the formation of BiNWs on the GC substrate. Phase-purity of the deposited BiNWs on GC substrate studied by XRD indicates no other oxide formation. The electrodeposited BiNWs on GC substrate was used for electro-reduction of folic acid (FA) and its quantitative determination in Britton-Robinson buffer of pH 4.5 solutions. The observed cyclic voltammetric reduction current of FA on BiNWs/GC is almost 15 times higher with 0.015V less negative overpotential compared to bare GC substrate alone. This result clearly reveals the electrocatalytic activity of the deposited BiNWs. In addition, square wave voltammetry (SWV) showed a perfectly linear response in the concentration range of 1×10−8–15×10−8molL−1 with a correlation coefficient of 0.9956. The limit of detection (LOD) and limit of quantitation (LOQ) are determined to be 9.53×10−9 and 31.68×10−9molL−1 respectively. The response of the BiNWs/GC sensor matrix is not affected by any usual interference from excess concentrations of metal ions and biomolecules such as ascorbic acid, dopamine, and glucose. Further, we have also performed real sample analysis using pharmaceutical tablets containing folic acid using our BiNWs/GC in the form of recovery studies and the obtained results are found to be in good agreement with the results from high performance liquid chromatography analysis (HPLC). Based on the experimental results, it may be stated that the electrodeposited BiNWs/GC could be an ideal sensor platform for FA determination and may open up applications in biosensor design.

Surface-Energy Induced Formation of Single Crystalline Bismuth Nanowires over Vanadium Thin Film at Room Temperature

We report high-yield room-temperature growth of vertical single-crystalline bismuth nanowire array by vacuum thermal evaporation of bismuth over a choice of arbitrary substrate coated with a thin interlayer of nanoporous vanadium. The nanowire growth is the result of spontaneous and continuous expulsion of nanometer-sized bismuth domains from the vanadium pores, driven by their excessive surface energy that suppresses the melting point of bismuth close to room temperature. The simplicity of the technique opens a new avenue for the growth of nanowire arrays of a variety of materials.

Recrystallized Arrays of Bismuth Nanowires with Trigonal Orientation

We demonstrate methods to improve the crystalline-quality of free-standing Bi nanowires arrays on a Si substrate and enhance the preferred trigonal orientation for thermoelectric performance by annealing the arrays above the 271.4 °C Bi melting point. The nanowires maintain their geometry during melting due to the formation of a thin Bi-oxide protective shell that contains the molten Bi. Recrystallizing nanowires from the melt improves crystallinity; those cooled rapidly demonstrate a strong trigonal orientation preference.

Electronic phases, band gaps, and band overlaps of bismuth antimony nanowires

We have developed an iterative one-dimensional model to study the narrow band gap and the associated nonparabolic dispersion relations for bismuth antimony nanowires. An analytical approximation has also been developed. Based on the general model we have developed, we have calculated and analyzed the electronic phase diagrams and the band-gap/band-overlap map for bismuth antimony nanowires, as a function of stoichiometry, growth orientation, and wire width.

22pm1-E5 石英ガラスを利用したBiナノワイヤーの作製と熱電物性の評価

Enhancement of the dimensionless thermoelectric figure of merit ZT is predicted theoretically in nanowires. In our study, we developed bismuth nanowires encapsulated in quartz templates. Bismuth nanowires were fabricated by injecting molten bismuth into a nano-scale hole of the quartz template and then recrystallized by cooling the temperature gradually. From 50-nm to 1-μm-diameter bismuth nanowires were successfully obtained by utilizing this fabrication technique. The measurement of the Seebeck coefficient and the electrical resistivity in the same nanowire sample is the first in the world. Differences between the thermoelectric properties of nanowires and bulk were observed in detail. A decrease of the carrier mobility was predicted by analyzing these thermoelectric properties with theoretical calculation considering the mean free path limitation. Therefore, new electrodes fabrication procedure for measurements of the Hall coefficient and the four-wire resistance of bismuth wires was established utilizing focused-ion-beam processing in order to evaluate the carrier mobility.

Thermoelectric Nanowire Junction Photoresponse

ABSTRACTRecently there have been reports of hot carrier thermoelectric response in nanostructured materials like graphene and MoS. We report observing that thermoelectric nanowire junctions detect light. In these experiments we employed devices composed of bismuth nanowire arrays which are capped with a transparent indium tin oxide electrode. The incident surface features very low optical reflectivity and enhanced light trapping. The unique attributes of the thermoelectric arrays are the combination of strong temporal and optical wavelength dependences of the photocurrent. Under infrared illumination, the signal can be completely described by “quasi-equilibrium” thermoelectric effects considering cooling rates given by heat diffusion through the array. The thermal diffusivity is found to be less (by a factor of 3.5) than in the bulk, a result that we discuss in terms of phonon confinement effects. In addition to a thermoelectric response, under visible illumination, we observe a photovoltaic response.

Bi nanowire-based thermal biosensor for the detection of salivary cortisol using the Thomson effect

We present a study of a thermal biosensor based on bismuth nanowire that is fabricated for the detection of the human stress hormone cortisol using the Thomson effect. The Bi nanowire was grown using the On-Film Formation of Nanowires (OFF-ON) method. The thermal device was fabricated using photolithography, and the sensing area was modified with immobilized anti-cortisol antibodies conjugated with protein G for the detection of cortisol. The voltages were measured with two probe tips during surface modification to investigate the biochemical reactions in the fabricated thermal biosensor. The Bi nanowire-based thermal biosensor exhibited low detection limit and good selectivity for the detection of cortisol.

Focused ion beam processing to fabricate ohmic contact electrodes on a bismuth nanowire for Hall measurements

Ohmic contact electrodes for four-wire resistance and Hall measurements were fabricated on an individual single-crystal bismuth nanowire encapsulated in a cylindrical quartz template. Focused ion beam processing was utilized to expose the side surfaces of the bismuth nanowire in the template, and carbon and tungsten electrodes were deposited on the bismuth nanowire in situ to achieve electrical contacts. The temperature dependence of the four-wire resistance was successfully measured for the bismuth nanowire, and a difference between the resistivities of the two-wire and four-wire methods was observed. It was concluded that the two-wire method was unsuitable for estimation of the resistivity due to the influence of contact resistance, even if the magnitude of the bismuth nanowire resistance was greater than the kilo-ohm order. Furthermore, Hall measurement of a 4-μm-diameter bismuth microwire was also performed as a trial, and the evaluated temperature dependence of the carrier mobility was in agreement with that for bulk bismuth, which indicates that the carrier mobility was successfully measured using this technique.PACS81.07.Gf