Bi2Te3 Nanowires Research Articles

Investigation of Electrodeposition of Bi2Te3 Nanowires into Nanoporous Alumina Templates with a Rotating Electrode

A rotating electrode was employed to investigate the electrodeposition of Bi2Te3 nanowires. We found that mass transport of electrolytes into alumina templates of high aspect ratio plays a significant role in determining the properties of the obtained wires since diffusion is the rate-determining mechanism of mass transport within these nanochannels. In addition to slow growing rate, the effect of mass transport causes a slight composition variation from the bottom to the top of the wires. With a rotating electrode, the composition variation along the wires can be reduced by shortening the concentration depleted zone from the bulk electrolyte to the opening of pores. The wire growing rate can consequently be increased. Moreover, the wire compositions were confirmed to be adjustable by varying the rotation speed under the limitation of using a thin template.

Pulsed electrodeposition of single-crystallineBi2Te3 nanowire arrays

Thermoelectric material Bi2Te3 nanowire arrays have been successfully prepared by pulsed electrochemical deposition intothe nanochannels of porous anodic alumina membranes. X-ray diffraction analyses showthat the as-synthesized nanowires have a highly preferential orientation. Scanning electronmicroscopy, transmission electron microscopy, and high-resolution transmissionelectron microscopy observations indicate that the high-filling-rate and uniformBi2Te3 nanowires are single crystalline. Energy dispersive spectrometer analyses indicate that thecompositions of the nanowires can be controlled by changing the potentials and thesolution concentrations. The electrical resistance measurements indicate that theresistances increase with decreasing temperature and show a typical semiconductorcharacteristic. The growth mechanism is discussed together with the electrochemicaldeposition process studies.

Growth and Characterization of 1D Bi2Te3 Nanowires

ABSTRACTBulk bismuth telluride (Bi2Te3) is one of the best known thermoelectric materials with a figure of merit ZT ∼1 at room temperature. Theoretical studies have suggested that low-dimensional materials may exhibit ZT values that exceed 1. In this study, we used the pulsed laser vaporization (PLV) method to prepare Bi2Te3 nanowires on silicon and quartz substrates by ablating Bi2Te3 targets in an inert atmosphere. Nano-sized gold or iron catalyst particles were used to seed the growth of the Bi2Te3 nanowires. Results from electron microscopy and Raman spectroscopy are discussed.

Thermal properties of electrodeposited bismuth telluride nanowires embedded in amorphous alumina

Bismuth telluride nanowires are of interest for thermoelectric applications because of the predicted enhancement in the thermoelectric figure-of-merit in nanowire structures. In this letter, we carried out temperature-dependent thermal diffusivity characterization of a 40nm diameter Bi2Te3 nanowires∕alumina nanocomposite. Measured thermal diffusivity of the composite decreases from 9.2×10−7m2s−1 at 150Kto6.9×10−7m2s−1 at 300K and is lower than thermal diffusivity of unfilled alumina templates. Effective medium calculations indicate that the thermal conductivity along nanowires axis is at least an order of magnitude lower than thermal conductivity of the bulk bismuth telluride.

Micro instrumentation for characterizing thermoelectric properties of nanomaterials

A micro tool for evaluating thermoelectric properties of low-dimensional materials is developed. It is expected that a one-dimensional thermoelectric material exhibits superior thermoelectric properties and low thermal conductivity due to its inherent nanoscale structure. By using these superior properties, high efficient thermoelectric power transformation devices may be realized. In this study, we developed micro instrumentation fabricated by micromachining for the characterization of thermoelectric properties of low-dimensional materials. The device consists of freely suspended heating elements and built-in microthermocouple as a sensing element on the heating elements. A bundle of Bi2Te3 nanowire, which is prepared by a silicon template method, was positioned onto the microdevice by manipulation. Measurements of the electric conductivity, thermal conductivity and Seebeck coefficient of the Bi2Te3 bundle were performed to show the feasibility of this device for measurements of thermoelectric properties of nanomaterials.

Bismuth Telluride (Bi2Te3) Nanowires Synthesized by Cyclic Electrodeposition/Stripping Coupled with Step Edge Decoration

Polycrystalline bismuth telluride (Bi2Te3) nanowires have been prepared by the step edge selective electrodeposition of Bi2Te3 on highly oriented pyrolytic graphite (HOPG) surfaces. Bi2Te3 nanowires were obtained from an aqueous plating solution containing Bi3+ and HTeO2+ using a three-step procedure: (1) potentiostatic oxidation of the graphite surface at +0.8 V (vs saturated calomel electrode, SCE), (2) potentiostatic nucleation of Bi2Te3 at −0.6 V for 5 ms, (3) growth of Bi2Te3 from these nuclei by cyclic electrodeposition (of both Bi2Te3 and bismuth) and stripping (of bismuth only) between +0.30 V and −0.05 V at 20 mV s-1. Control of the number of electrodeposition/stripping scans allowed the diameter of Bi2Te3 nanowires to be specified in the range from 100 to 300 nm. Bi2Te3 nanowires were narrowly dispersed in diameter (RSDdia = 10−20%), were up to 1.0 mm in length, and were organized into parallel arrays containing hundreds of wires.

Electrochemically assembled p-type Bi2Te3 nanowire arrays

Polycrystalline Bi2Te3 nanowires with diameter about 50 nm have been assembled into the nanopores of alumina template by electrodeposition in the solution containing Bi3+ and HTeO2+ with porous alumina template as a cathode. X-ray photoelectron spectroscopy, high-resolution electron microscopy, and selected area electron diffraction investigations indicate that the nanowires are polycrystalline Bi2Te3 with hexagonal structure. Transmission electron microscopy and environmental scanning electron microscopy are used to characterize the morphology of the Bi2Te3 nanowire arrays. The performance measurements verified that the Seebeck coefficient of p-type Bi2Te3 nanowire arrays prepared in our lab was 270 μV/K at 306 K, which is larger than that of bulk Bi2Te3 thermoelectric materials. The temperature dependence of the resistance of the nanowire arrays was also measured, and it showed a semiconductive characteristic.

Electrochemical Fabrication of Large-Area, Ordered Bi2Te3 Nanowire Arrays

Thermoelectric material Bi2Te3 has been successfully synthesized by cathodic electrolysis into porous anodic alumina membranes. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and electron diffraction (ED) results show that the as-synthesized samples are hexagonal Bi2Te3 single-crystal nanowires. The morphologies and structure of the Bi2Te3 nanowires have been characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrate that the Bi2Te3 nanowire arrays with a high-filling rate and a large area are dense, continuous, and smooth. Energy dispersive spectrometer (EDS) analysis indicates that the atomic ratio of Bi to Te is very close to 2:3 stoichiometry.

Bismuth, tellurium, and bismuth telluride nanowiresElectronic supplementary information (ESI) available: additional TEM images and XRD patterns. See http://www.rsc.org/suppdata/jm/b3/b312820b/

Decomposition of the precursor Bi[N(SiMe3)2]3 in the presence of poly(1-hexadecene)0.67-co-(1-vinylpyrrolidinone)0.33 and a small amount of NaN(SiMe3)2 in 1,3-diisopropylbenzene solution at 203 °C gives Bi nanowires. The single-crystalline wires are several micrometers in length, and possess a mean diameter of 5.9 ± 2.4 nm. Decomposition of TeCl4 in the presence of TOPO in polydecene solution at 250–300 °C gives Te nanowires. These nanowires are also single crystals exhibiting micrometer lengths. The Te nanowire mean diameters are in the range of 30–60 nm, and depend upon the reaction conditions employed. Attempts to grow Bi2Te3 nanowires from reactions of Bi- and Te-containing molecular precursors produce other Bi2Te3 crystallite morphologies. Efforts to convert Bi nanowires into Bi2Te3 nanowires are also unsuccessful. However, reactions of Te nanowires and BiPh3 in polydecene solution at 160 °C do afford continuous Bi2Te3 nanowires, having micrometer lengths and mean diameters larger than those of the precursor Te nanowires. The Bi2Te3 nanowires are found to be encased in amorphous sheath structures, which apparently enforce the one-dimensional wire morphologies.

Solvothermal preparations of nanocrystalline Bi2Te3 powders and the study on their characterizations

[Abstract] Bi2Te 3 nanoparticles of 15∼25nm were prepared via solvothermal processes in which pyridine, absolute ethanol and distilled water were used as reaction medium respectively. The XRD and TEM have been applied to analyze the samples, and the grain sizes have also been calculated by Scherrer Equation. The results showed that in these experiments, all of the reaction products' purity, crystallization, grain size and tropism increased with dielectric constant and polarity of the solvent. A novel Bi2Te3 nanowires with several tens to a hundred nanometers diameter and up to more than ten microns length have been prepared when distilled water was used as reaction medium.

Structure of Bismuth Telluride Nanowire Arrays Fabricated by Electrodeposition into Porous Anodic Alumina Templates

Arrays of bismuth telluride (Bi2Te3) nanowires with diameters of ∼25, ∼50, and ∼75 nm have been produced by electrochemical deposition into porous anodic alumina templates. Scanning electron microscopy confirms that the nanowire arrays are dense with a narrow distribution of nanowire diameters. The structure of the nanowires was assessed immediately after deposition, after annealing to ∼80% of the melting point, and after melting/recrystallization. As determined by XRD analysis, there is strong fiber texture in the arrays that depends on both the nanowire diameter and the postdeposition processing conditions. Bright-field/dark-field imaging and diffraction in the transmission electron microscope reveal that the as-deposited nanowires are polycrystalline with a bamboo-type grain structure that does not change significantly upon annealing, and a similar grain structure is obtained after melting and resolidification.

Control and Assessment of Structure and Composition in Bismuth Telluride Nanowire Arrays

ABSTRACTDue to effects of reduced dimensionality, Bi2Te3 nanowires are predicted to have increased thermoelectric efficiency relative to bulk Bi2Te3, one of the most efficient thermoelectric materials known. High-density arrays of nanowires have desirable characteristics for accessing nanowire properties in potential applications and also allow for facile nanowire property assessment. Here we describe a fabrication method to produce Bi2Te3 nanowire arrays by direct current electrochemical deposition into porous anodic alumina templates. The characteristics of the arrays have been assessed to determine the composition and structure in the arrays as well as in individual nanowires. Thefabricated arrays have a high-density of uniform diameter (∼40nm), high aspect ratio wires that are stoichiometric, polycrystalline Bi2Te3.

High Spatial Resolution Assessment of the Structure, Composition, and Electronic Properties of Nanowire Arrays

AbstractWe have employed transmission electron microscopy (TEM) and analytical electron microscopy to perform preliminary assessment of the structure, composition and electronic properties of nanowire arrays at high spatial resolution. The two systems studied were bismuth and bismuth telluride nanowire arrays in alumina (wire diameters ~40nm), both of which are promising for thermoelectric applications. Imaging coupled with diffraction in the TEM was employed to determine the grain size in electrodeposited Bi2Te3 nanowires. In addition, a composition gradient was identified along the wires in a short region near the electrode by energy-dispersive x-ray spectroscopy. Electron energy loss spectroscopy combined with energy-filtered imaging in the TEM revealed the excitation energy and spatial variation of plasmons in bismuth nanowire arrays.

Synthesis of Single Crystal Bismuth-Telluride and Lead-Telluride Nanowires for New Thermoelectric Materials

ABSTRACTDimensionality can play an important role in determining the properties of materials. In the case of thermoelectric materials, it has been proposed that one-dimensional quantum wires, or nanowires, and two-dimensional superlattices could exhibit substantially higher efficiencies compared to the corresponding bulk, three-dimensional solids. To explore such predictions we have initiated a program directed towards the controlled growth of nanowires, and herein, we report the synthesis of single crystal Bi2Te3 and PbTe nanowires by a pulsed laser ablation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Bi2Te3 wires 80 nm to 200 nm in diameter and lengths exceeding 10 microns, and PbTe wires 25 nm to 60 nm in diameter and lengths to 2 microns can be readily produced by the laser ablation method. High-resolution TEM and electron diffraction show that Bi2Te3 nanowires are single crystals with wire axes along the <110> crystal direction. TEM and electron diffraction measurements also show that the PbTe nanowires are single crystals with a <100> growth axis. The transport properties of these new nanowire materials will be discussed.