Telluride Nanowires Research Articles

High Seebeck Coefficient BiSbTe Nanowires

Bismuth antimony telluride (BiSbTe) nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid electrolyte. Optimum deposition potentials were obtained from polarization and compositional analysis. X-ray diffraction analysis showed a preferential (015) orientation for the nanowires. The Bi 2 Sb 0.6 Te 3 nanowire sample deposited at —150 mV showed a high Seebeck coefficient (S) of -630 μV/K.

Optical limiting properties of Te and Ag 2Te nanowires

We have prepared tellurium (Te) and silver telluride (Ag 2Te) nanowires in solution and investigated their nonlinear optical transmission by the open-aperture z-scan technique, using nanosecond laser pulses, at the excitation wavelengths of 532 and 1064 nm. The nonlinearity has contributions from absorption saturation, excited state absorption and nonlinear scattering processes. The saturation intensity and nonlinear absorption coefficient are calculated numerically. Nonlinear absorption in Ag 2Te nanowires is found to be one order of magnitude higher than that in Te nanowires. Observation of optical limiting at both excitation wavelengths indicates the potential of these materials to be used as broadband optical limiters.

Thermoelectric Properties of Electrodeposited BiSbTe Nanowires

AbstractBismuth antimony telluride (BiSbTe) nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid baths having different electrolyte compositions. Composition analysis of the nanowires showed that Sb deposits at higher potentials compared to BiTe. Maximum seebeck coefficients of -337.7 μV/K and 227.2 μV/K were obtained for n-type and p-type nanowires samples Bi4.6Te5.4 and Bi4.3Sb5 respectively. Nonmonotonic resistance behavior was observed for all the nanowires.

Disproportionation of thermoelectric bismuth telluride nanowires as a result of the annealing process

P-type thermoelectric bismuth telluride nanowires were fabricated by pulsed electrodeposition in anodic aluminium oxide (AAO) membranes. Subsequently, the nanowires were annealed at 423, 523 and 673 K in an inert atmosphere for 4 h. With increasing temperature, it was observed that the Te compound incongruently sublimates due to its high vapor pressure, leading to disproportionation (from Bi(2)Te(3) to Bi(4)Te(3)via Bi(4)Te(5)). The crystalline structure of the nanowires was then investigated using XRD and SAED, with nanowire compositions investigated using an EDX attached to a TEM. The crystallinity of the nanowires was found to be enhanced with increased annealing temperature, and nanowires annealed at 673 K were stably maintained in the Bi(4)Te(3) phase. Additionally, the Seebeck coefficient was determined and the thermopower of nanowires annealed at a temperature of 423 K was shown to be slightly enhanced. Significantly suppressed Seebeck values for annealing temperatures of 523 K and 673 K were also observed.

Electrodeposition and Characterization of Bismuth Telluride Nanowires

In this work, we report thermoelectric measurements on electroplated bismuth telluride nanowires. Porous polycarbonate membranes, obtained by ion-track irradiation lithography, were chosen as electroplating templates. Bismuth telluride nanowires were achieved in acidic media under potentiostatic conditions at −100 mV versus saturated silver chloride electrode. The filling ratio of the pores was increased to 80% by adding dimethyl sulfoxide to the electrolyte. Whatever the experimental conditions, the nanowires were polycrystalline in the rhombohedral phase of Bi2Te3. Finally, the power output of arrays of bismuth telluride nanowires was analyzed as a function of load resistance. The results were strongly dependent on the internal resistance, which can be significantly reduced by the presence of dimethyl sulfoxide during electroplating.

Wafer-Scale Patterning of Lead Telluride Nanowires: Structure, Characterization, and Electrical Properties

Nanowires of lead telluride (PbTe) were patterned on glass surfaces using lithographically patterned nanowire electrodeposition (LPNE). LPNE involved the fabrication by photolithography of a contoured nickel nanoband that is recessed by approximately 300 nm into a horizontal photoresist trench. Cubic PbTe was then electrodeposited from a basic aqueous solution containing Pb(2+) and TeO(3)(2-) at the nickel nanoband using a cyclic deposition/stripping potential program in which lead-rich PbTe was first deposited in a negative-going potential scan and excess lead was then anodically stripped from the nascent nanowire by scanning in the positive direction to produce near stoichiometric PbTe. Repeating this scanning procedure permitted PbTe nanowires 60-400 nm in width to be obtained. The wire height was controlled over the range of 20-100 nm based upon the nickel film thickness. Nanowires with lengths exceeding 1 cm were prepared in this study. We report the characterization of these nanowires using X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The surface chemical composition of PbTe nanowires was monitored by XPS as a function of time during the exposure of these nanowires to laboratory air. One to two monolayers of a mixed Pb and Te oxide are formed during a 24 h exposure. The electrical conductivity of PbTe nanowires was strongly affected by air oxidation, declining from an initial value of 2.0(+/-1.5) x 10 (4) S/m by 61% (for nanowires with a 20 nm thickness), 55% (for 40 nm), and 12% (for 60 nm).

Coaxial nanocables of p-type zinc telluride nanowires sheathed with silicon oxide: synthesis,characterization and properties

Coaxial nanocables with a single-crystalline zinc telluride (ZnTe) nanowire core and an amorphous siliconoxide (SiOx) shell have been synthesized via a simple one-step chemical vapor deposition(CVD) method on gold-decorated silicon substrates. The single-crystal ZnTenanowire core is in zinc-blende structure along the [111] direction, while the uniformSiOx shell fully covers the core with no observable pin-hole or crack. Formation mechanisms of theZnTe–SiOx nanocables are discussed. The ZnTe nanowire core shows p-type electrical properties while theSiOx shell acts as an effective insulating layer. TheZnTe–SiOx nanocables may have potential applications in nanoscale devices, such as p-type FETs andnanosensors.

Room-Temperature Chemical Synthesis of Silver Telluride Nanowires

We have developed a room-temperature solution-phase route for the preparation of one-dimensional silver telluride nanowires (Ag2Te NWs). The Ag2Te NWs of 600 nm length and 20 nm diameter were synthesized by the reaction of tellurium nanowires (Te NWs) with silver nitrate (AgNO3) in water. We propose that Te NWs act as the template and the reducing agent simultaneously, enabling the formation of polycrystalline Ag2Te NWs. Various microscopic and spectroscopic tools, such as HRTEM, SEM, EDAX, XRD, DSC, XPS, and Raman, were used for the characterization of Ag2Te NWs. The phase transition corresponding to the structural transition from the low-temperature monoclinic phase to the high-temperature face-centered cubic phase occurs at 417.7 K. We studied the electrical resistance and investigated the influence of temperature on the thermal emf. The Seebeck coefficient showed a maximum of ∼142 μV K−1, a value much higher than that of the bulk material and thin films (65−130 μV K−1). A surface-enhanced Raman scattering investigation of dispersed Ag2Te NWs showed them to be sensitive up to 10−7 M crystal violet. The monodispersity and the homogeneity of the NWs through a simple solution-phase protocol would pave the way for further studies and applications.

Electrodeposition and Thermoelectric Characterization of Bismuth Telluride Nanowires

Bismuth telluride nanowires were electrodeposited from aqueous acidic solutions containing different (20/20 and 20/10 mM) concentration ratios. The polarization plots predicted that combined solutions exhibit more noble reduction potentials than individual solutions. Optimized deposition potentials were obtained from the combined electrolyte polarization plots. An anomalous codeposition behavior caused an increase in Te concentration for depositions in the kinetic region of bismuth telluride; otherwise, decreasing Te concentrations with increased deposition potentials was observed from a composition analysis. X-ray diffraction showed a dominant (110) orientation for nanowires at low deposition potentials. n-Type nanowires were obtained from both electrolytes, while p-type nanowires were only obtained from the 20/10 electrolyte for low Te concentrations. An intrinsic to extrinsic transition was observed for nanowires deposited from the 20/10 electrolyte. The highest measured Seebeck coefficient was and for n- and p-type nanowires, respectively. The Seebeck coefficient dependence on the resistivity and composition of the nanowires is discussed.

Thermoelectric and structural characterizations of individual electrodeposited bismuth telluride nanowires

The thermoelectric properties and crystal structure of individual electrodeposited bismuth telluride nanowires (NWs) were characterized using a microfabricated measurement device and transmission electron microscopy. Annealing in hydrogen was used to obtain electrical contact between the NW and the supporting Pt electrodes. By fitting the measured Seebeck coefficient with a two-band model, the NW samples were determined to be highly n-type doped. Higher thermal conductivity and electrical conductivity were observed in a 52 nm diameter monocrystalline NW than a 55 nm diameter polycrystalline NW. The electron mobility of the monocrystalline NW was found to be about 19% lower than that of bulk crystal at a similar carrier concentration and about 2.5 times higher than that of the polycrystalline NW. The specularity parameter for electron scattering by the NW surface was determined to be about 0.7 and partially specular and partially diffuse, leading to a reduction in the electron mean-free path from 61 nm in the bulk to about 40 nm in the 52 nm NW. Because of the already short phonon mean-free path of about 3 nm in bulk bismuth telluride, diffuse phonon-surface scattering is expected to reduce the lattice thermal conductivity of the 52–55 nm diameter NWs by only about 20%, which is smaller than the uncertainty in the extracted lattice thermal conductivity based on the measured total thermal conductivity and calculated electron thermal conductivity. Although the lattice thermal conductivity of the polycrystalline NW is likely lower than the bulk values, the lower thermal conductivity observed in this polycrystalline sample is mainly caused by the lower electron concentration and mobility. For both samples, the thermoelectric figure of merit (ZT) increases with temperature and is about 0.1 at a temperature of 400 K. The low ZT compared to that of bulk crystals is mainly caused by a high doping level, suggesting the need for better control of the chemical composition in order to improve the ZT of the electrodeposited NWs. Moreover, bismuth telluride NWs with diameter less than 10 nm would be required for substantial suppression of the lattice thermal conductivity as well as experimental verification of theoretical predictions of power factor enhancement in quantum wires. Such stringent diameter requirement can be relaxed in other NW systems with longer bulk phonon mean-free path or smaller effective mass and thus longer electron wavelength than those in bulk bismuth telluride.

Enhancement of the Thermoelectric Figure of Merit in Gated Bismuth Telluride Nanowires

AbstractWe theoretically studied how the electric filed effect can modify thermoelectric properties of intrinsic bismuth telluride nanowires, which are grown along [110] direction. The electronic structure and wave functions were calculated by solving the self-consistent system of the Schrodinger and Poisson equations by means of both the Thomas-Fermi approximation and the spectral element method. The thermoelectric parameters were determined using a constant relaxation-time approximation. The external electric field can increase the Seebeck coefficient of a nanowire with 7 - 15 nm lateral dimensions by nearly a factor of two, and enhance the figure of merit by an order of magnitude.

Thermoelectric properties of bismuth telluride nanowires in the constant relaxation-time approximation

Electronic structure of bismuth telluride nanowires with the growth directions [110] and [015] is studied in the framework of the anisotropic effective-mass method using the parabolic band approximation. The components of the electron and hole effective-mass tensors for six valleys are calculated for both growth directions. For a square nanowire, in the temperature range from 77 to 500 K, the dependence of the Seebeck coefficient $S$, the thermal $\ensuremath{\kappa}$, and electrical conductivity $\ensuremath{\sigma}$, as well as the figure of merit $ZT$ on the nanowire thickness and on the excess hole concentration ${p}_{ex}$, are investigated in the constant relaxation-time approximation. The carrier confinement is shown to play essential role for nanowires with cross section less than $30\ifmmode\times\else\texttimes\fi{}30\text{ }{\text{nm}}^{2}$. In contrast to the excess holes (impurities), the confinement decreases both the carrier concentration and the thermal conductivity but increases the maximum value of the Seebeck coefficient. The confinement effect is stronger for the direction [015] than for the direction [110] due to the carrier mass difference for these directions. In the restricted temperature range, the size quantum limit is valid when the $\mathbit{P}$-type nanowire cross section is smaller than $8\ifmmode\times\else\texttimes\fi{}10\text{ }{\text{nm}}^{2}$ ($6\ifmmode\times\else\texttimes\fi{}7$ and $5\ifmmode\times\else\texttimes\fi{}5\text{ }{\text{nm}}^{2}$) at the excess hole concentration ${p}_{\text{ex}}=2\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}$ (${p}_{\text{ex}}=5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}$ and ${p}_{\text{ex}}=1\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }{\text{cm}}^{\ensuremath{-}3}$ correspondingly). The carrier confinement increases the maximum value of $ZT$ and shifts it toward high temperatures. For the growth direction [110], the maximum value of the figure of merit for the $\mathbit{P}$-type nanowire is equal to 1.4, 1.6, and 2.8, correspondingly, at temperatures 310, 390, and 480 K and the cross sections $30\ifmmode\times\else\texttimes\fi{}30$, $15\ifmmode\times\else\texttimes\fi{}15$, and $7\ifmmode\times\else\texttimes\fi{}7\text{ }{\text{nm}}^{2}$ $({p}_{\text{ex}}=5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3})$. At room temperature, the figure of merit equals 1.2, 1.3, and 1.7, respectively.

Phase-Transition-Dependent Conductivity and Thermoelectric Property of Silver Telluride Nanowires

Silver telluride nanowires have been synthesized by the composite-hydroxide-mediated (CHM) method at temperatures of 180−225 °C. The products were single-crystalline nanowires and monoclinic phase Ag2Te with a high purity. The reversible structural phase transition from monoclinic structure (β-Ag2Te) to face-centered cubic structure (α-Ag2Te) around 148/133 °C was observed during the heating/cooling process. The latent heat of the phase transition was calculated. The electrical resistance and thermal emf versus temperature were for the first time investigated on the Ag2Te nanowires. Abrupt changes of conductivity and Seebeck coefficient around the phase transition temperature were observed. The maximum Seebeck coefficient is ∼170 and ∼160 μV K−1 during the heating and cooling process, respectively, indicating a promising one-dimensional thermoelectric material as a building block to construct nanodevices.

Axial-Junction Nanowires of Ag2Te−Ag As a Memory Element

Silver telluride nanowires incorporating silver were prepared by green chemical method in aqueous solution. First, Ag2TeO3 was prepared from aqueous solutions of sodium tellurite (Na2TeO3) and silver nitrate (AgNO3). At room temperature in basic solution, α-d-glucose reduces Ag2TeO3 to generate silver nanocrystals, whereas solvothermal reaction of Ag2TeO3 with α-d-glucose at 165 °C generates Te, Ag, or Ag2Te−Ag axial hetrojunction nanowires depending upon the pH of the reaction mixture. These heterojunction nanowires, which exhibit electrical bistability at low voltage, can be used as data storage devices.

Tuning the crystallinity of thermoelectricBi2Te3 nanowire arrays grown by pulsed electrodeposition

Arrays of thermoelectric bismuth telluride(Bi2Te3)nanowires were grown into porous anodic alumina (PAA) membranes prepared by a two-step anodization.Bi2Te3 nanowire arrays were deposited by galvanostatic, potentiostatic and pulsedelectrodeposition from aqueous solution at room temperature. Depending on theelectrodeposition method and as a consequence of different growth mechanisms,Bi2Te3 nanowires exhibit different types of crystalline microstructure.Bi2Te3 nanowire arrays, especially those grown by pulsed electrodeposition, have a highly orientedcrystalline structure and were grown uniformly as compared to those grown by otherelectrodeposition techniques used. X-ray diffraction (XRD) analyses are indicative of theexistence of a preferred growth orientation. High resolution transmission electronmicroscopy (HRTEM) and selected area electron diffraction (SAED) confirm the formationof a preferred orientation and highly crystalline structure of the grown nanowires. Thenanowires were further analyzed by scanning electron microscopy (SEM). Energydispersive x-ray spectrometry (EDX) indicates that the composition of Bi–Tenanowires can be controlled by the electrodeposition method and the relaxationtime in the pulsed electrodeposition approach. The samples fabricated by pulsedelectrodeposition were electrically characterized within the temperature range240 K≤T≤470 K.Below T≈440 K, the nanowire arrays exhibited a semiconducting behavior. Dependingon the relaxation time in the pulsed electrodeposition, the semiconductorenergy gaps were estimated to be 210–290 meV. At higher temperatures, as aconsequence of the enhanced carrier–phonon scattering, the measured electricalresistances increased slightly. The Seebeck coefficient was measured for everyBi2Te3 sample at room temperature by a very simple method. All samples showed a positive value(12–33 µV K−1), indicating a p-type semiconductor behavior.

Synthesis of PbTe Nanowire Arrays using Lithographically Patterned Nanowire Electrodeposition

We describe the preparation by electrodeposition of arrays of lead telluride (PbTe) nanowires using the lithographically patterned nanowire electrodeposition (LPNE) method. PbTe nanowires had a rectangular cross-section with adjustable width and height ranging between 60-400 nm (w) and 20-100 nm (h). The characterization of these nanowire arrays using X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS) is reported. PbTe nanowires were electrodeposited using a cyclic electrodeposition-stripping technique that produced polycrystalline, stoichiometric, face-centered cubic PbTe with a mean grain diameter of 10-20 nm. These nanowires were more than 1 mm in length and two additional processing steps permitted their suspension across 25 microm air gaps microfabricated on these surfaces. The LPNE synthesis of lithographically patterned PbTe nanowires was carried out in unfiltered laboratory air. Nanowires with lengths of 70-100 microm showed an electrical resistivity comparable to bulk PbTe. XPS reveals that exposure of PbTe nanowires to air causes the formation on the nanowire surface of approximately one monolayer of a mixed lead oxide and tellurium oxide within a few minutes.

Synthesis and characterization of cadmium telluride nanowire

CdTe nanowires with controlled composition were cathodically electrodeposited usingtrack-etched polycarbonate membrane as scaffolds and their material and electricalproperties were systematically investigated. As-deposited CdTe nanowires shownanocrystalline cubic phase structures with grain sizes of up to 60 nm. The dark-fieldimages of nanowires reveal that the crystallinity of nanowires was greatly improvedfrom nanocrystalline to a few single crystals within nanowires upon annealing at200 °C for 6 h in a reducingenvironment (5% H2+95% N2). For electrical characterization, a single CdTe nanowire was assembled acrossmicrofabricated gold electrodes using the drop-casting method. In addition to anincrease in grain size, the electrical resistivity of an annealed single nanowire (a few105 Ω cm) was one order of magnitude greater than in an as-deposited nanowire,indicating that crystallinity of nanowires improved and defects withinnanowires were reduced during annealing. By controlling the dopants levels(e.g. Te content of nanowires), the resistivity of nanowires was varied from104 to100 Ω cm.Current–voltage (I–V) characteristics of nanowires indicated the presence of Schottky barriersat both ends of the Au/CdTe interface. Temperature-dependentI–V measurements show that the electron transport mode was determined by a thermally activated componentat T>−50 °C and a temperature-independent component below−50 °C. Under optical illumination, the single CdTe nanowire exhibited enhanced conductance.

Structural Characterization and Thermoelectric Transport Properties of Uniform Single-Crystalline Lead Telluride Nanowires

Uniform single-crystalline PbTe nanowires with average diameter of about 30 nm, below its average excitonic Bohr radius of 46 nm, were successfully synthesized in large quantity by a two-step hydrothermal process using tellurium nanowires as templates and Pb(NO 3) 2 as a precursor. It is shown that the reaction temperature, duration, and concentration of Pb(NO 3) 2 play important roles in the formation of the PbTe nanowires. An in situ diffusion and growth mechanism together with a nontopotactic transformation process was proposed to explain the formation of the PbTe nanowires. The thermoelectric transport measurement indicates a high Seebeck coefficient of about 628 μV/K in the thin film sample composed of the obtained PbTe nanowires, about 137% exceeding that of the state-of-the-art bulk PbTe. The calculated local density of states (LDOS) by the density functional theory shows a strong increase with decreasing nanowire diameter, which is consistent with the measured large enhancement in Seebeck coeffici...

Synthesis and characterisation of CZT nanowire arrays for gamma ray detection

A single step pulsed potential electrodeposition of cadmium zinc telluride (CZT) nanowires was carried out in propylene carbonate solution at 130°C onto a nanotubular TiO2 template. Various combinations of potential pulses were investigated and the electrochemical parameters were optimised to obtain nanowires with a stoichiometry of Cd0.96Zn0.04Te. The CZT nanowires showed an electrical resistivity of 4.48 × 109 Ω-cm and an electronic band gap of 1.53 eV after annealing at 350°C for 1 h in argon atmosphere. The CZT nanowires grown on semiconductor nanotubular TiO2 templates can be integrated into a detection device for sensing low-medium energy gamma rays.

Template Electrodeposition of Ordered Bismuth Telluride Nanowire Arrays

Thermoelectric bismuth telluride nanowire arrays have been synthesized by direct-current electrode-position into porous anodic alumina membranes both galvanostatically and potentiostatically. The as-synthesized Bi2Te3 nanowire arrays are highly ordered in large area, stoichiometric, uniform, with high aspect ratio (above 100) and high filling ratio (>90%) of the membrane. The effects of different electrochemical deposition parameters on crystal structures, morphology and composition have been investigated. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) have been used to characterize the physical and chemical properties of the nanowires.