Zhongyu Hou

Field-effect transistor based on /spl beta/-SiC nanowire

/spl beta/-SiC nanowires were synthesized by the way of high-frequency induction with diameter range between 10 to 25 nm and the length was up to 10 /spl mu/m. Field-effect transistor was fabricated with those synthesized /spl beta/-SiC nanowires. The carrier mobilities of the n-type SiCFETs were 6.4 and 15.9 cm/sup 2//V/spl middot/s when V/sub ds/ is 0.01 and 0.05 V at room temperature, respectively. At high temperature, the drain current increased by one order of magnitude than it did at room temperature. The carrier mobility versus 1000/T agreed well with the Arrhenius function. The SiCFETs in this letter would be used as electrical devices operated in high temperatures because of their superior properties.

Poly (acrylic acid sodium) grafted carboxymethyl cellulose as a high performance polymer binder for silicon anode in lithium ion batteries

The design of novel binder systems is required for the high capacity silicon (Si) anodes which usually undergo huge volume change during the charge/discharge cycling. Here, we introduce a poly (acrylic acid sodium)-grafted-carboxymethyl cellulose (NaPAA-g-CMC) copolymer as an excellent binder for Si anode in lithium ion batteries (LIBs). The NaPAA-g-CMC copolymer was prepared via a free radical graft polymerization method by using CMC and acrylic acid as precursors. Unlike the linear, one-dimensional binders, the NaPAA-g-CMC copolymer binder is expected to present multi-point interaction with Si surface, resulting in enhanced binding ability with Si particles as well as with the copper (Cu) current collectors, and building a stable solid electrolyte interface (SEI) layer on the Si surface. The NaPAA-g-CMC based Si anode shows much better cycle stability and higher coulombic efficiency than those made with the well-known linear polymeric binders such as CMC and NaPPA.

Ionization gas sensing in a microelectrode system with carbon nanotubes

An efficient technology for manufacturing high-performance ionization gas sensors using carbon nanotubes as electrode materials that identify gases in some short sampling distance is developed in this letter. The microarray with five sensor units of different gap sizes (S≈6, 7, 8, 10, and 12μm) can break down gases at distinct threshold voltages and currents depending on the gap size and gas species. The quite low operation voltage, high accuracy, and chip-based nature may be considered as significant improvements in ionization gas sensors.

A MEMS-Based Ionization Gas Sensor Using Carbon Nanotubes

We demonstrate here the successful operation of an ionization gas sensor with a gap spacing S of 2 or 7plusmn0.4 mum and using carbon nanotubes as the electrode material. The device is chip based and fabricated using a microelectromechanical system process. Application of a bias of 0.6-1.8 V (Sap2 mum) or 12-15 V (Sap7 mum) to the electrodes generates an electric field that is sufficient to field ionize He, CO2, and their mixtures in air with high sensitivity and selectivity. The approach is considered as effective for lowering the operation voltage of ionization gas sensors below 36 V (safety voltage criterion) and is significant for the development of the smart device in this field

Application of carbon nanotubes to human breath dynamics characterization

The carbon nanotube composite material and its fabrication techniques are introduced to construct a chip-based electrode system for human breath dynamics characterization. The application of 10V dc bias can generate electric field high enough to effectively collect the charged particles in the human breath. Without using breath collecting tubes, the field tests in the open air exhibit that the system is technologically promising for long-time and noncontact human breath dynamics monitoring, due to its high stability, sensitivity, and safety operation performance with power consumption in the order of 10−5W.

Ionization gas sensing of the ion flow current in a microtripolar electrode system with carbon nanotubes

We report the tests of a tripolar on-chip microelectrode system with carbon nanotubes, where the ion flow current (Ii) and the partial discharge current produced by the field ionization process of gaseous molecules can be measured to characterize the gas species and concentration. A theoretical account is given regarding the underlying differences between their sensing mechanisms. Further, comparative analysis of these two outputs in response to the concentration dynamic changes of ethanol/acetone in N2 demonstrates the explicit cases of improved sensitivity and selectivity of the Ii measurement.

Mechanism of gas breakdown near Paschen’s minimum in electrodes with one-dimensional nanostructures

The mechanism of the gaseous breakdown in the electrode system with one-dimensional (1D) nanomaterial film is investigated. The hypothesis is suggested that the functionality of the 1D nanostructures in the breakdown is the averaged flux-convergence-effect of multiple nanoelectrodes to the electric field distribution, which leads to a convergence band model for discharge modeling. Theoretical deductions are examined by experiments in air and N2 at pressures (p) near the Paschen’s minimum with gap sizes (d) of ∼335 μm and pd range of 0.01–1 Torr cm. It is suggested that the increased efficiency of the secondary processes and the discharge’s lateral spreading may characterize the breakdown mechanism in electrodes with 1D nanostructures.

Sensing of atomized liquids through field effects of polarization and ionization induced by nanostructures

The mechanism and instrumentation of an atomized liquid sensing system is presented, characterizing the dynamic polarization and ionization processes of liquid droplets in an electric field converged by one dimensional nanostructures. The microarchitecture implementing the mechanism is realized by microlithography technology. It is shown that the current amplitude is a function of both droplets’ flow rate and its chemistry; thus, one of them can be differentiated when the other is a constant. Further, the current-time spectrum responding to the vaporization and diffusion processes can enhance the differentiability. The methodology can be applied to atomized liquid sensing or liquid chemistry differentiation.

Nanocoating covalent organic frameworks on nickel nanowires for greatly enhanced-performance supercapacitors

Nanocoatings of covalent organic frameworks (COFs) on nickel nanowires (NiNWs) have been designed and successfully fabricated for the first time, which showed greatly enhanced electrochemical performances for supercapacitors. The specific capacitance of electrodes based on as-fabricated COFs nanocoatings reached up to 314 F g-1 at 50 A g-1, which retained 74% of the specific capacitance under the current density of 2 A g-1. The ultrahigh current density makes the charge-discharge process extremely rapid. The outstanding electrochemical performances of COFs nanocoating on NiNWs make it an ideal candidate for supercapacitors. And the nanocoating-design can also give a guidance for application of COFs in high-performance energy storages.

Direct current dielectric barrier discharges under voltages below the ionization potential of neutrals in electrode systems with one-dimensional nanostructures

We experimentally investigate the characteristics of dielectric barrier discharges in an electrode system with one-dimensional nanostructures of gap size at micrometer scale. Evidence of quasistationary direct current discharges in air has been observed under the applied voltage several times lower than the first ionization potential of O2. The results qualitatively agree with the hypothesis on the ionization mechanism of stepwise inelastic collisions within a metastable pool, which is populated through field excitation and inelastic impact between the neutrals and the nanostructures.