Bingchu Cai

Giant magnetoimpedance in layered FeSiB/Cu/FeSiB films

The giant magnetoimpedance (GMI) effect has been studied in layered FeSiB/Cu/FeSiB films in the frequency range of 100 kHz–40 MHz. The field dependence of the GMI ratio shows that the GMI ratio increases with magnetic field Ha, reaching a positive maximum value at a certain field, and then gradually decreases to negative values. For the layered films with a Cu film width of 0.6 mm, the positive maximum GMI ratio is about 2%, which is smaller than the value of the negative GMI ratio (−6.6% at Ha=50 Oe) at a frequency of 5.2 MHz. With an increase of the Cu film width, a positive maximum GMI ratio of 4.5% and 13.5% is obtained for Ha=30 Oe and 5.2 MHz in the layered films with a Cu film widths of 1 and 1.3 mm respectively. In addition, all the layered films exhibit a large negative GMI ratio at a relatively large field and it is associated with the easy axis orientation of the layered films. The increase of the positive maximum GMI ratio with an increase of Cu film width at 5.2 MHz may be due not only to the...

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.

Fabrication and performance of a novel suspended RF spiral inductor

A novel suspended radio frequency (RF) spiral inductor was fabricated on glass substrate by using the microelectromechanical systems (MEMS) technology. The suspended spiral inductor is sustained with the T-shaped pillars. Great improvements in Q-factor have been achieved because of the separation between the substrate and the inductor. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure the seed layer and the pillars contact perfectly, and dry etching technique is used to remove the seed layer. The inductance and Q-factor are measured using the HP 8722D network analyzer in the frequency range of 0.05-10 GHz. The maximum quality factor of this inductor is 37 for the inductance of 4.2 nH with a suspended height of 60 /spl mu/m. Also, the relationship between the maximum quality factor and the suspended height were studied; the maximum quality factor grows gradually with the increase of the suspended height.

Giant magneto-impedance effect in amorphous magnetostrictive FeSiB thin films

Giant magneto-impedance (MI) effect has been observed in amorphous magnetostrictive FeSiB thin films with the transverse magnetic anisotropy induced by applying a magnetic field of 800 Oe during deposition. The MI effect is enhanced with increasing film thickness, and the maximum MI ratio reaches 5.4% for the films with 2.7 μm in thickness at 40 MHz. Experimental results show that the magnetic anisotropy in FeSiB films plays an important role in large MI effect.

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.

Controlled assembly of FePt nanoparticles monolayer on solid substrates

The surface wettability is one of the most important factors to control the morphology of nanoparticle arrangement on the solid substrates. The various morphologies of FePt nanoparticles were fabricated on different substrates with different wetting surfaces by the Langmuir-Blodgett (LB) technology at large scale. A highly ordered structure and a dense arrangement of FePt nanoparticle monolayer were obtained on different substrates with contact angle up to 66°. The air pockets could be presented between the nanoparticles and solid substrate by theoretical analysis, because FePt nanoparticles had hydrophobic surface. A net structure of FePt nanoparticles on solid substrates could be also obtained by controlling about 45° contact angles of their surfaces. This method potentially opens up a new approach to controlling assembly of nanoparticle monolayer on solid substrates by change of the wettability on the surfaces of solid substrate and provides a promising thin film which may exhibit the excellent ultra high density magnetic recording properties.