Yanguo Wang

High-performance lithium-ion battery anode by direct growth of hierarchical ZnCo2O4 nanostructures on current collectors.

Hierarchical nanostructures that can be directly grown on a conducting substrate are a new trend in the design of active materials for high-performance lithium-ion batteries (LIBs). This article reports our design and fabrication of a 3D hierarchical ZnCo2O4 nanostructure (3D-ZCO-NS) directly grown on Ni foams. The goose-feather-like ZnCo2O4 bundled into a loose array structure with a large electrolyte contact area and good electrical and mechanical connection to the current collector. Electrochemical measurements confirmed the good performance of the electrode for reversible Li(+) storage (specific capacity of 932 mAh g(-1) in the 50th cycle at 1 A g(-1)) relative to a pasted electrode of 3D-ZCO-NSs (599 mAh g(-1) in the 50th cycle at 0.1 A g(-1)).

Rational design of Au–NiO hierarchical structures with enhanced rate performance for supercapacitors

Hierarchical structures consisting of highly conductive Au nanoparticles decorated on NiO nanostructures could significantly improve electrical conductivity. Herein, the Au–NiO composite exhibits greatly improved rate performance as pseudo-capacitors, and a high specific capacitance value of 619 F g−1 at a high rate of 20 A g−1, which is much higher than that of pure NiO electrodes (216 F g−1).

Direct Observations of Nanofilament Evolution in Switching Processes in HfO2‐Based Resistive Random Access Memory by In Situ TEM Studies

Resistive switching processes in HfO2 are studied by electron holography and in situ energy-filtered imaging. The results show that oxygen vacancies are gradually generated in the oxide layer under ramped electrical bias, and finally form several conductive channels connecting the two electrodes. It also shows that the switching process occurs at the top interface of the hafnia layer.

The large-scale synthesis of one-dimensional TiO2 nanostructures using palladium as catalyst at low temperature

The synthesis of TiO(2) nanostructures including nanowires and nanobelts has been demonstrated experimentally by anodization of Ti foil in an electrolyte, and by treatment in a PdCl(2) ethanol solution together with UV light irradiation and annealing at a temperature below 800 degrees C. The TiO(2) nanotube arrays resulting from the anodization were used as source precursor and transformed into nanowires and nanobelts respectively with high efficiency during the subsequent processes. The resulting TiO(2) nanowires and nanobelts, characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman and surface photovoltage (SPV) spectroscopy, are single rutile crystals of high quality. In addition to the synthesis of the nanostructure at low temperature, this method also shows great advantages for the selectable morphology of the final TiO(2) nanostructures via adjustment of the UV light irradiation time and annealing temperature.

Dynamic observation of oxygen vacancies in hafnia layer by in situ transmission electron microscopy

The charge-trapping process, with HfO2 film as the charge-capturing layer, has been investigated by using in situ electron energy-loss spectroscopy and in situ energy-filter image under positive external bias. The results show that oxygen vacancies are non-uniformly distributed throughout the HfO2 trapping layer during the programming process. The distribution of the oxygen vacancies is not the same as that of the reported locations of the trapped electrons, implying that the trapping process is more complex. These bias-induced oxygen defects may affect the device performance characteristics such as the device lifetime. This phenomenon should be considered in the models of trapping processes.

Cathode-Control Alloying at an Au-ZnSe Nanowire Contact via in Situ Joule Heating

Controllable interfacial alloying is achieved at a Au-ZnSe nanowire (M-S) contact via in situ Joule heating inside transmission electron microscopy (TEM). TEM inspection reveals that the Au electrode is locally molten at the M-S contact and the tip of the ZnSe nanowire is covered by the Au melting. Experimental evidences confirm that the alloying at the reversely biased M-S contact is due to the high resistance of the Schottky barrier at this M-S contact, coincident to cathode-control mode. Consequently, in situ Joule heating can be an effective method to improve the performance of nanoelectronics based on a metal-semiconductor-metal nanostructure.

The influence of P on glass forming ability and clusters in melt of FeSiBP amorphous soft-magnetic alloy

AbstractOurn experiment focused on investigating the P content dependences of the ability to form glass, the soft-magnetic properties of, and the clusters in melting Fe85−xSi4B11Px (xxa0=xa01–6), amorphous soft-magnetic alloys. The experimental results demonstrate that the alloys with proper P content (3–6 at.%) are prone to form a completely amorphous structure with a larger glass-forming ability (GFA); hence, amorphous alloys prepared by industry-grade raw materials can be well produced in an air atmosphere. The melted alloy has higher stability and larger GFA when there is no dominant cluster or when multi-species clusters coexist. The Fe82Si4B11P3 amorphous alloy exhibited a high saturation magnetic flux density of up to 1.66 T, a low coercivity of about 2.2xa0A/m, and a high effective permeability of more than 1.2xa0×xa0104 at 1xa0kHz under a field of 1xa0A/m. The combination of excellent soft-magnetic properties, good productivity and low cost stability suggest that the FeSiBP alloys are promising soft-magnetic materials, particularly with applications in the electronic industry.

The Evolution of Microstructure and Magnetic Properties of the Bismuth Layer Compounds with Cobalt Ions Substitution

One of the core issues for the A/B site doping in the bismuth layer magnetoelectric materials is to find out the evolution of the magnetic structure, crystal structure and elemental distribution, and the coupling effects between spin and lattice with the increase of ion substitution. Here, we have conducted systematic structural and physical property studies on the series samples of Bi5Ti3Fe1-xCoxO15. This work presents that Bi5Ti3Fe1-xCoxO15 forms a single four layer perovskite-like structure for 0 ≤ x < 0.67, while a three layer perovskite-like structure block begins to arise for x ≥ 0.67. With different cobalt content, the sample demonstrates antiferromagnetism, spin state determined magnetism, or magnetic anisotropy determined magnetism. The weak ferromagnetism is considered to be induced by the larger displacement of Co3+ ions from the center of octahedra and the change of the spin state of Co3+ ions. It is also observed that Fe and Co elements are homogeneously substituted in the three layer structure block, accompanied by the rotation (and/or distortion) of BO6 octahedra.

Enhanced Current Carrying Capability of Au-ZnSe Nanowire-Au Nanostructure via High Energy Electron Irradiation

To enhance the performance of nanoelectronics based on Au-ZnSe nanowire (NW)-Au (M-S-M) nanostructure, the effect of irradiation of the high energy electron beam emitted from the electron gun of a transmission electron microscope operated at 200 kV on the current carrying capability of M-S-M nanostructure is investigated in situ. Focusing the high energy electron beam on a Au electrode, the current carrying capability of the M-S-M nanostructure can be enhanced significantly with respect to the case of the electron beam being switched off. In this case, the electrons in the electrode are excited by the incident high energy electron and can freely tunnel through the Schottky barriers at the metal-semiconductor NW (M-S) nanocontacts, which can effectively reduce Joule heat dissipation and remarkably improve the current carrying capability of M-S-M nanostructure due to the fact that the current carrying capability highly depends on the Joule heating effect of Schottky barriers at M-S nanocontacts.