Ion-track etched templates for the high density growth of nanowires of bismuth telluride and bismuth antimony telluride by electrodeposition

We report the electrochemical growth of high density arrays of n- type Bi2Te3 and p-type Bi0.5Sb1.5Te3 nanowires into ion-track etched polyimide-based Kapton membranes with a density of 5 x 109 wires/cm2. The average diameter of the nanowires is 80 nm with a length of 20 µm, which is comparable to the pore size and thickness of the employed Kapton foils. The electroplating parameters and microstructural properties are reported for the nanowires whilst thermoelectric properties have been investigated for thin films of Bi2Te3 and Bi0.5Sb1.5Te3

High density p-type Bi0.5Sb1.5Te3 nanowires by electrochemical templating through ion-track lithography

High density p-type Bi0.5Sb1.5Te3 nanowire arrays are produced by a combination of electrodeposition and ion-track lithography technology. Initially, the electrodeposition of p-type wBi(0.5)Sb(1.5)Te(3) films is investigated to find out the optimal conditions for the deposition of nanowires. Polyimide-based Kapton foils are chosen as a polymer for ion track irradiation and nanotemplating Bi0.5Sb1.5Te3 nanowires. The obtained nanowires have average diameters of 80 nm and lengths of 20 mu m, which are equivalent to the pore size and thickness of Kapton foils. The nanowires exhibit a preferential orientation along the {110} plane with a composition of 11.26 at.% Bi, 26.23 at.% Sb, and 62.51 at.% Te. Temperature dependence studies of the electrical resistance show the semiconducting nature of the nanowires with a negative temperature coefficient of resistance and band gap energy of 0.089 +/- 0.006 eV

Enhanced Thermoelectric Properties of a Semiconducting Two-Dimensional Metal–Organic Framework via Iodine Loading

We report the first result of a study in which molecular iodine has been incorporated via incipient wetness impregnation into the two-dimensional semiconducting metal–organic framework (MOF) Cu3(2,3,6,7,10,11-hexahydroxytriphenylene)2 Cu3(HHTP)2 to enhance its thermoelectric properties. A power factor of 0.757 μW m–1 K–2 for this MOF was obtained which demonstrates that this provides an effective route for the preparation of moderate-performance thermoelectric MOFs

Understanding the selective etching of electrodeposited ZnO nanorods

ZnO nanotubes were prepared by selective dissolution of electrodeposited nanorods. The effect of solution pH, rod morphology, and chloride ion concentration on the dissolution mechanism was studied. The selective etching was rationalized in terms of the surface energy of the different ZnO crystal faces and reactant diffusion. The nanorod diameter and chloride concentration are the most influential parameters on the dissolution mechanism because they control homogeneous dissolution or selective etching of the (110) and (002) surfaces. Bulk solution pH only has an effect on the rate of dissolution. By accurate control of the dissolution process, the nanomorphology can be tailored, and the formation of rods with a thin diameter (10-20 nm), cavity, or ultra-thin-walled tubes (2-5 nm) can be achieved

Three-Dimensional Nanostructured Palladium with Single Diamond Architecture for Enhanced Catalytic Activity

Fuel cells are a key new green technology that have applications in both transport and portable power generation. Carbon-supported platinum (Pt) is used as an anode and cathode electrocatalyst in low-temperature fuel cells fueled with hydrogen or low-molecular-weight alcohols. The cost of Pt and the limited world supply are significant barriers to the widespread use of these types of fuel cells. Comparatively, palladium has a 3 times higher abundance in the Earth’s crust. Here, a facile, low-temperature, and scalable synthetic route toward three-dimensional nanostructured palladium (Pd) employing electrochemical templating from inverse lyotropic lipid phases is presented. The obtained single diamond morphology Pd nanostructures exhibited excellent catalytic activity and stability toward methanol, ethanol, and glycerol oxidation compared to commercial Pd black, and the nanostructure was verified by small-angle X-ray scattering, scanning tunneling electron microscopy, and cyclic voltammetry

Electrochemically copper-doped bismuth tellurium selenide thin films

We report the first results of a study on electrochemically doped copper bismuth tellurium selenide thin films electrodeposited from aqueous nitric acid electrolytes containing up to 2 mM of Cu(NO3)2. The effect of Cu(NO3)2 concentration on the composition, structure and thermoelectric properties of the bismuth tellurium selenide films is investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Seebeck and Hall effect measurements. A Cu(NO3)2 concentration of 1.5 mM is found to offer a Seebeck coefficient of up to −390 μV K−1 at room temperature, which is the highest reported to date for an electrodeposited bismuth tellurium compound

Electrochemical deposition of bismuth telluride thick layers onto nickel

Bismuth telluride (Bi2Te3) is the currently best performing thermoelectric (TE) material in commercial TE devices for refrigeration and waste heat recovery up to 200 °C. Up to 800 μm thick, compact, uniform and stoichiometric Bi2Te3 films were synthesized by pulsed electrodeposition from 2 M nitric acid baths containing bismuth and tellurium dioxide on 1 cm2 nickel (Ni) substrates at average film growth rates of ~ 50 μm/h. Pre-treatment of the Ni substrate was found to significantly enhance the adhesion of Bi2Te3 material onto Ni while pulsed electrodeposition was used to increase the compactness of the material. To maintain a homogeneous composition across the thickness of the films, a sacrificial Bi2Te3 anode was employed. All deposits produced were n-type with a Seebeck coefficient of up to − 80 μV/K and an electrical conductivity of ~ 330 S/cm at room temperature

The early stages of CdTe epitaxial growth on gold single crystal electrode surfaces

In this dissertation an investigation into the initial phases of epitaxial CdTe monolayer film growth onto the low index planes of gold employing in-situ scanning tunnelling microscopy (STM) is presented. The CdTe films were grown by the sequential deposition of a partial monolayer of Te and Cd at underpotentials using Electrochemical Atomic Layer Epitaxy (ECALE). Atomic resolution images of the first UPD structures of tellurium prior to Cd deposition have been obtained in a CdSO4 solution indicating the stability of these adlayers towards emersion from solution. A new Te UPD structure could be imaged on the Au(111) surface under these conditions which could not be observed in previous ex-situ and in-situ studies. This exhibited a characteristic row morphology with long range ordering and could be identified as having a (3x9) unit cell registry with the underlying Au(111) substrate.The CdTe films were found to grow two-dimensionally in a layer-by-layer fashion. On the basis of detailed potential step experiments a refined mechanism for the observed structural transition from an initial (2x2) Te overlayer to a c(2x2) structure upon Cd UPD on the Au(100) surface is proposed, which has so far been a matter of some controversy in the literature. Atomically resolved STM images on the Au (111) and Au(110) plane revealed well-ordered CdTe structures with hexagonal symmetry. The adlayer unit cells were found to be consistent with a (3x3) and a (2x3) overlayer structure. The kinetics of CdTe electrocrystallization were studied by performing scan rate dependent cyclic voltammetry experiments. An analysis of this cyclic voltammetry data suggested that the Cd monolayer formation and dissolution Te modified gold surfaces proceeds by an instantaneous two-dimensional nucleation and growth mechanism.The results of an in-situ STM study in combination with ultra-high vacuum (UHV) electrochemical transfer experiments using x-ray photoelectron spectroscopy (XPS) and low-energy diffraction (LEED) on underpotentially deposited tellurium layers on Au(hkl) are also reported.</p