Guodong Wu

Fabrication and optical properties of TiO2 nanowire arrays made by sol-gel electrophoresis deposition into anodic alumina membranes

Ordered TiO2 nanowire arrays have been successfully fabricated into the nanochannels of a porous anodic alumina membrane by sol–gel electrophoretic deposition. After annealing at 500°C, the TiO2 nanowire arrays and the individual nanowires were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and x-ray diffraction (XRD). SEM and TEM images show that these nanowires are dense and continuous with a uniform diameter throughout their entire length. XRD and SAED analysis together indicate that these TiO2 nanowires crystallize in the anatase polycrystalline structure. The optical absorption band edge of TiO2 nanowire arrays exhibits a blue shift with respect of that of the bulk TiO2 owing to the quantum size effect.

A novel synthesis route to Y2O3:Eu nanotubes

Large-scale Y2O3:Eu nanotubes have been successfully fabricated by an improved sol–gel method within the nanochannels of porous anodic alumina templates. In this method, yttrium nitrate, europium nitrate and urea were used as precursors, yttrium nitrate and europium nitrate were acting as sources of europium and yttrium ions, and urea offered a basic medium through its hydrolysis. X-ray diffraction techniques, scanning electron microscopy, transmission electron microscopy and selected-area electron diffraction were used to characterize the Y2O3:Eu nanotubes obtained. It is found that the prepared Y2O3:Eu nanotubes can be indexed as a polycrystalline cubic structure and their outer diameters are about 50–80 nm, with the thickness of the tube wall estimated to be around 5 nm. The emission peaks of the as-prepared Y2O3:Eu nanotubes are broader than those of bulk Y2O3:Eu because of the disordering of the crystal phase possibly induced by the increase of the surface/volume ratio in the nanotubes.

Self-assembly synthesis and magnetic studies of Co–P alloy nanowire arrays

The paper describes the self-assembly synthesis of Co–P alloy nanowire arrays in an anodic alumina membrane (AAM) by electroless deposition and presents their corresponding magnetic properties. The images of Co–P alloy nanowire arrays and single nanowires are obtained by scanning electron microscopy and transmission electron microscopy, respectively. Selected area electron diffraction, x-ray diffraction and energy dispersive spectra are employed to study the morphology and chemical composition of the nanowires. The results show that Co–P alloy nanowire arrays are amorphous. The magnetic properties of Co–P alloy nanowire arrays is characterized using a vibrating sample magnetometer. The hysteresis loops indicate that the easily magnetized direction of Co–P nanowire arrays is parallel to the nanowire arrays and has obvious magnetic anisotropy as a result of the shape anisotropies. Electroless deposition can be extended to many other materials and opens up significant opportunities in nanoscalar fabrication magnetic materials for ultra-high-density magnetic recoding media. Compared with the electrodeposition method, electroless deposition need not supply power or sprinkle Au on one side of the AAM before deposition and some defects of electrodeposition can be overcome.

An interface nanostructured array guided high performance electrochemical actuator

Here we report a novel electrochemical actuator using a hierarchically architectured nanostructure electrode. Vertically aligned NiO nanowall arrays, which act as an interface layer, are in situ grown on a free-standing graphene–carbon nanotube hybrid film. The large specific surface area and fast ion transmission channels of this nanostructured array interface enable us to achieve large deformation in quick switching response (18.4 mm per 0.05 s), high strain and stress rates (8.31% s−1, 12.16 MPa s−1) and excellent durability upon 500 000 times continuous operations in air.

Synthesis of SnO2 nanostructures by carbothermal reduction of SnO2 powder

The mass preparation of SnO2 nanobelts and nanowires has been achieved by carrying out the reaction of SnO2 powder and graphite at 1150°C. A metallic catalyst and vacuum conditions are not necessary. The temperature of the substrates and the concentration of oxide vapour were the critical experimental parameters for the formation of different morphologies of SnO2 nanostructures. The as-synthesized SnO2 nanobelts formed in region II are single crystalline with a [101] growth axis, with widths ranging from 50 to 500 nm, width-to-thickness ratios of 5–10, and lengths up to a few millimetres.

Artificial Synaptic Devices Based on Natural Chicken Albumen Coupled Electric-Double-Layer Transistors

Recent progress in using biomaterials to fabricate functional electronics has got growing attention for the new generation of environmentally friendly and biocompatible electronic devices. As a kind of biological material with rich source, proteins are essential natural component of all organisms. At the same time, artificial synaptic devices are of great significance for neuromorphic systems because they can emulate the signal process and memory behaviors of biological synapses. In this report, natural chicken albumen with high proton conductivity was used as the coupling electrolyte film for organic/inorganic hybrid synaptic devices fabrication. Some important synaptic functions including paired-pulse facilitation, dynamic filtering, short-term to long-term memory transition and spatial summation and shunting inhibition were successfully mimicked. Our results are very interesting for biological friendly artificial neuron networks and neuromorphic systems.

Chitosan-based biopolysaccharide proton conductors for synaptic transistors on paper substrates

Chitosan is a natural biopolymer and has been widely used for bio- and medical-materials. In this letter, with protonic acid doping, chitosan-based biopolysaccharide proton conductors were prepared with a high proton conductivity of 6 x 10(-3) S cm(-1) at room temperature and were first used for fabricating synaptic transistors on paper substrates. Based on the movement of protons with pulse voltage response within the chitosan dielectrics in a coplanar-gate transistor configuration, the paper synaptic transistors could be successfully used as artificial synapses for emulating biological synaptic functions. Short-term plasticity behaviors, including paired-pulse facilitation, dynamic filtering and spatiotemporally correlated signal processing were mimicked. Our results strongly demonstrate that these biopolysaccharide gating synaptic transistors proposed here are not only important for building cheap and biologically friendly artificial neuron networks, but also are interesting for realizing intelligent biomaterials.

Flexible Transparent Junctionless TFTs With Oxygen-Tuned Indium-Zinc-Oxide Channels

Flexible low-voltage transparent junctionless thin-film transistors (TFTs) with oxygen-tuned indium-zinc-oxide (IZO) active layers are fabricated on polyethylene terephthalate plastic substrates at room temperature with only one shadow mask. IZO films deposited in gradient oxygen ambient are used as the channel and source/drain electrodes without any source/drain junction. High performance with a low subthreshold swing of 0.13 V/decade and a high drain current ON/OFF ratio 106 are obtained in both flat and curving states. A field-effect mobility with a upper limit value of ~60 cm2/V.s is obtained with a gate voltage sweep speed of 0.05 V/s. Such flexible IZO-based junctionless TFTs with lowcost are promising for portable flexible sensor and bioelectronics applications.

Tungsten oxide proton conducting films for low-voltage transparent oxide-based thin-film transistors

Tungsten oxide (WOx) electrolyte films deposited by reactive magnetron sputtering showed a high room temperature proton conductivity of 1.38 × 10−4 S/cm with a relative humidity of 60%. Low-voltage transparent W-doped indium-zinc-oxide thin-film transistors gated by WOx-based electrolytes were self-assembled on glass substrates by one mask diffraction method. Enhancement mode operation with a large current on/off ratio of 4.7 × 106, a low subthreshold swing of 108 mV/decade, and a high field-effect mobility 42.6 cm2/V s was realized. Our results demonstrated that WOx-based proton conducting films were promising gate dielectric candidates for portable low-voltage oxide-based devices.

Dual in-plane-gate oxide-based thin-film transistors with tunable threshold voltage

Dual in-plane-gate oxide-based thin-film transistors (TFTs) are self-assembled on SiO2-based solid-electrolytes by only one shadow mask. The unique feature of such TFTs is that indium-tin-oxide (ITO) channel and four ITO electrodes can be deposited simultaneously. Threshold voltage can be effectively tuned from −0.55 V to 0.76 V when the second in-plane gate bias switches from 3.0 V to −2.0 V. Such dual-gate TFTs exhibit a large current on/off ratio (>106) and a small subthreshold swing (<200 mV/decade). A model based on three gate capacitors is proposed to further understand the operation mechanism of such devices.