Electrochemical synthesis of ultrafast and gram-scale surfactant-free tellurium nanowires by gas-solid transformation and their applications as supercapacitor electrodes for p-doping of graphene transistors.

We herein report a gas-solid transformation mechanism for the surfactant-free synthesis of Te NWs at room temperature by electrolysis of bulk Bi2Te3 using H2Te gas. Te NWs, with an average diameter below 20 nm, grow along the [001] direction due to the unique spiral chains in the crystal structure and show an enhanced Raman scattering effect, a broad absorption band over the range of 350-750 nm and an emission band over the range of 400-700 nm in the photoluminescence spectrum. In terms of device applications, we demonstrate how Te NWs can be directly applied as a p-type dopant source in order to shift the Dirac point in ambipolar field effect graphene transistors. Finally, the favorable capacitive properties of Te NWs are established as supercapacitor electrodes with negligible internal resistance and excellent electrochemical reversibility and a specific capacitance of 24 F g(-1).

Growth of large-scale nanotwinned Cu nanowire arrays from anodic aluminum oxide membrane by electrochemical deposition process: controllable nanotwin density and growth orientation with enhanced electrical endurance performance.

Densely nanotwinned Cu nanowire (NW) arrays with an identical diameter of ∼55 nm were fabricated by pulse electrochemical deposition at low temperature using anodic aluminum oxide as a template. Different growth orientations of nanotwinned Cu nanowire arrays were investigated. The endurance of the electrical current density before breakdown of the nanotwinned Cu NWs can reach up to 2.4 × 10(8) A cm(-2). The formation of highly dense nanotwins is attributed to relaxation of coalescence induced stress and twin fault stacking when Cu NWs grow by two-dimensional kinetics. A mechanism based on the twinning structure effect on the electromigration was proposed to explain the improved electrical endurance of Cu. The result demonstrates that the formation of nanotwins into Cu NWs can effectively suppress the void growth, leading to extended life time for use in electronic devices.

Fabrication of large-scale single-crystal bismuth telluride (Bi2Te3) nanosheet arrays by a single-step electrolysis process.

Nanolizing of thermoelectric materials is one approach to reduce the thermal conductivity and hence enhance the figure of merit. Bismuth telluride (Bi2Te3)-based materials have excellent figure of merit at room temperature. For device applications, precise control and rapid fabrication for the nanostructure of thermoelectric materials are essential issues. In the present study, we demonstrate a one-step electrolysis process to directly form Bi2Te3 nanosheet arrays (NSAs) on the surface of bulk Bi2Te3 with controllable spacing distance and depth by tuning the applied bias and duration. The single sheet of NSAs reveals that the average thickness and electrical resistivity of single crystalline Bi2Te3 in composition are 399.8 nm and 137.34 µΩ m, respectively. The formation mechanism of NSAs has been proposed. A 1.12% efficiency of quantum dot-sensitized solar cells with Bi2Te3 NSAs for counter electrode has been demonstrated, indicating that Bi2Te3 NSAs from top-down processing with a high ratio of surface area to volume are a promising candidate for possible applications such as thermoelectrics, dye-sensitized solar cells (DSSCs), and lithium-ion batteries.

Resistive switching of Au/ZnO/Au resistive memory: an in situ observation of conductive bridge formation.

A special chip for direct and real-time observation of resistive changes, including set and reset processes based on Au/ZnO/Au system inside a transmission electron microscope (TEM), was designed. A clear conducting bridge associated with the migration of Au nanoparticles (NPs) inside a defective ZnO film from anode to cathode could be clearly observed by taking a series of TEM images, enabling a dynamic observation of switching behaviors. A discontinuous region (broken region) nearby the cathode after reset process was observed, which limits the flow of current, thus a high resistance state, while it will be reconnected to switch the device from high to low resistance states through the migration of Au NPs after set process. Interestingly, the formed morphology of the conducting bridge, which is different from the typical formation of a conducting bridge, was observed. The difference can be attributed to the different diffusivities of cations transported inside the dielectric layer, thereby significantly influencing the morphology of the conducting path. The current TEM technique is quite unique and informative, which can be used to elucidate the dynamic processes in other devices in the future.