Effect of Fe and Zn co-doping on LiCoPO4 cathode materials for High-Voltage Lithium-Ion batteries.

Lithium cobalt phosphate (LiCoPO4) has great potential to be developed as a cathode material for lithium-ion batteries (LIBs) due to its structural stability and higher voltage platform with a high theoretical energy density. However, the relatively low diffusion of lithium ions still needs to be improved. In this work, Fe and Zn co-doped LiCoPO4: LiCo0.9-xFe0.1ZnxPO4/C is utilized to enhance the battery performance of LiCoPO4. The electrochemical properties of LiCo0.85Fe0.1Zn0.05PO4/C demonstrated an initial capacity of 118 mAh/g, with 93.4 % capacity retention at 1C after 100 cycles, and a good capacity of 87 mAh/g remained under a high current density of 10C. In addition, the diffusion rate of Li ions was investigated, proving the improvement of the materials with doping. The impedance results also showed a smaller resistance of the doped materials. Furthermore, operando X-ray diffraction displayed a good reversibility of the structural transformation, corresponding to cycling stability. This work provided studies of both the electrochemical properties and structural transformation of Fe and Zn co-doped LiCoPO4, which showed that 10 % Fe and 5 % Zn co-doping enhanced the electrochemical performance of LiCoPO4 as a cathode material in LIBs.

Cyclopentadithiophene-benzoic acid copolymers as conductive binders for silicon nanoparticles in anode electrodes of lithium ion batteries.

Cyclopentadithiophene and methyl-2,5-dibromobenzoate have been copolymerised via palladium complex catalysed direct arylation. The methyl ester group in the benzoate unit is converted to the carboxyl group via saponification. The polymers are mixed with Si nanoparticles for use as conducting binders in the fabrication of an anode electrode in lithium ion batteries. The battery with the electrode incorporating the saponified polymer shows much higher specific capacity of up to 1820 mA h g-1 (total weight) and a higher stability compared with the battery including the polymer before the saponification.

Hydrothermal phase transformation of hematite to magnetite.

Different phases of iron oxide were obtained by hydrothermal treatment of ferric solution at 200°C with the addition of either KOH, ethylenediamine (EDA), or KOH and EDA into the reaction system. As usually observed, the α-Fe2O3 hexagonal plates and hexagonal bipyramids were obtained for reaction with KOH and EDA, respectively. When both KOH and EDA were added into the reaction system, we observed an interesting phase transformation from α-Fe2O3 to Fe3O4 at low-temperature hydrothermal conditions. The phase transformation involves the formation of α-Fe2O3 hexagonal plates, the dissolution of the α-Fe2O3 hexagonal plates, the reduction of Fe(3+) to Fe(2+), and the nucleation and growth of new Fe3O4 polyhedral particles.

Au nanocrystal array/silicon nanoantennas as wavelength-selective photoswitches.

Au nanocrystal array/silicon nanoantennas exhibiting wavelength-selective photocurrent enhancement were successfully fabricated by a facile and inexpensive method combining colloidal lithography (CL) and a metal-assisted chemical etching (MaCE) process. The localized surface plasmon resonance (LSPR) response and wavelength-selective photocurrent enhancement characteristics were achieved by tuning the depth of immersion of Au nanocrystal arrays in silicon through a MaCE process. The wavelength selectivity of photocurrent enhancement contributed by LSPR induced local field amplification was confirmed by simulated near-field distribution. In addition, it can be integrated to well-developed Si-based manufacturing process. These characteristics make Au nanocrystal array/Si nanoantennas promising as low power-consumption photoswitches and nano-optoelectronic and photonic communication devices.

Micropatterned stretching system for the investigation of mechanical tension on neural stem cells behavior.

In this study, we developed a feasible and reliable stretching platform combined with photolithography and microfluidic techniques to investigate the effect of directional tensile force and guiding microchannel on neural stem cell (NSC) behavior. Different stretching modes and culture conditions were conducted to investigate the mechanoresponse of NSCs on micropatterned substrate and to verify the effects of tension on NSCs maturation, axon sprouting, neurite outgrowth and orientation. From the results, we found that neurite extension and axon elongation were significantly enhanced and neurites were more directional orientated to parallel direction as stretching was experienced. The mechanical tension apparently influenced NSCs differentiation toward neuronal cells under stretching condition. The neuronal maturity also showed a significant difference when compared with parallel and vertical micropatterned channels. It is suggested that mechanical tension not only can guide neurites orientation and direction, but also promote their elongation length and trigger neural stem cells differentiation into mature neuronal cells. FROM THE CLINICAL EDITOR: This group of investigators report the development of a feasible and reliable stretching platform combined with photolithography and microfluidic techniques to investigate the effects of directional tensile force and guiding microchannel on neural stem cell behavior. They demonstrate that neurite extension and axon elongation could be significantly enhanced, and neuronal maturity can also be improved.

Oxide-confined formation of germanium nanowire heterostructures for high-performance transistors.

Over the past several years, the formation of nanowire heterostructures via a solid-state reaction between a semiconductor nanowire and metal contact pads has attracted great interest. This is owing to its ready application in nanowire field-effect transistors (FETs) with a well-controlled channel length using a facile rapid thermal annealing process. We report the effect of oxide confinement on the formation of Ge nanowire heterostructures via a controlled reaction between a vapor-liquid-solid-grown, single-crystalline Ge nanowire and Ni pads. In contrast to the previous formation of Ni(2)Ge/Ge/Ni(2)Ge nanowire heterostructures, a segment of high-quality epitaxial NiGe was formed between Ni(2)Ge and Ge with the confinement of Al(2)O(3) during annealing. Significantly, back-gate FETs based on this Ni(2)Ge/NiGe/Ge/NiGe/Ni(2)Ge heterostructure demonstrated a high-performance p-type transistor behavior, showing a large on/off ratio of more than 10(5) and a high normalized transconductance of 2.4 µS/µm. The field-effect hole mobility was extracted to be 210 cm(2)/(V s). Temperature-dependent I-V measurements further confirmed that NiGe has an ideal ohmic contact to p-type Ge with a small Schottky barrier height of 0.11 eV. Moreover, the hysteresis during gate bias sweeping was significantly reduced after Al(2)O(3) passivation, and our Ω-gate Ge nanowire FETs using Al(2)O(3) as the top-gate dielectric showed an enhanced subthreshold swing and transconductance. Therefore, we conclude that the Al(2)O(3) layer can effectively passivate the Ge surface and also serve as a good gate dielectric in Ge top-gate FETs. Our innovative approach provides another freedom to control the growth of nanowire heterostructure and to further achieve high-performance nanowire transistors.

An ordered Si nanowire with NiSi2 tip arrays as excellent field emitters.

A method was developed to grow ordered silicon nanowire with NiSi(2) tip arrays by reacting nickel thin films on silica-coated ordered Si nanowire (NW) arrays. The coating of thin silica shell on Si NW arrays has the effect of limiting the diffusion of nickel during the silicidation process to achieve the single crystalline NiSi(2) NWs. In the meantime, it relieves the distortion of the NWs caused by the strain associated with formation of NiSi(2) to maintain the straightness of the nanowire and the ordering of the arrays. Other nickel silicide phases such as Ni(2)Si and NiSi were obtained if the silicidation processes were conducted on the ordered Si NWs without a thin silica shell. Excellent field emission properties were found for NiSi(2)/Si NW arrays with a turn on field of 0.82 V µm(-1) and a threshold field of 1.39 V µm(-1). The field enhancement factor was calculated to be about 2440. The stability test showed a fluctuation of about 7% with an applied field of 2.6 V µm(-1) for a period of 24 h. The excellent field emission characteristics are attributed to the well-aligned and highly ordered arrangement of the single crystalline NiSi(2)/Si heterostructure field emitters. In contrast to other growth methods, the present growth of ordered nickel silicide/Si NWs on silicon is compatible with silicon nanoelectronics device processes, and also provides a facile route to grow other well-aligned metal silicide NW arrays. The advantages will facilitate its applications as field emission devices.

Single-crystalline Ni2Ge/Ge/Ni2Ge nanowire heterostructure transistors.

In this study, we report on the formation of a single-crystalline Ni(2)Ge/Ge/Ni(2)Ge nanowire heterostructure and its field effect characteristics by controlled reaction between a supercritical fluid-liquid-solid (SFLS) synthesized Ge nanowire and Ni metal contacts. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal a wide temperature range to convert the Ge nanowire to single-crystalline Ni(2)Ge by a thermal diffusion process. The maximum current density of the fully germanide Ni(2)Ge nanowires exceeds 3.5 × 10(7) A cm(-2), and the resistivity is about 88 µΩ cm. The in situ reaction examined by TEM shows atomically sharp interfaces for the Ni(2)Ge/Ge/Ni(2)Ge heterostructure. The interface epitaxial relationships are determined to be [Formula: see text] and [Formula: see text]. Back-gate field effect transistors (FETs) were also fabricated using this low resistivity Ni(2)Ge as source/drain contacts. Electrical measurements show a good p-type FET behavior with an on/off ratio over 10(3) and a one order of magnitude improvement in hole mobility from that of SFLS-synthesized Ge nanowire.