Fabrication of semi-conductive ceramics by combination of gelcasting and reduction sintering

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s⁻¹, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 10⁶ Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details.     

Light-induced changes in the solar cell parameters and temperature coefficient of n-C/p-Si heterojunction solar cell

Amorphous carbon (a-C) is a potential material for the development of low-cost and high-efficiency solar cell. We report the study of the influence of light soaking up to 100 h on n-C/p-Si heterojunction solar cell. It is observed that the deterioration in the fill factor and the efficiency are significantly smaller as compared to that observed in a-Si:H solar cell. Variations in the temperature coefficients of the I–V characteristics subjected to light degradation and recovery has also been investigated. A good correlation between change in the temperature coefficient and the degradation/recovery state of cell's conversion efficiency has been observed.     

Mmic technology for communication systems

MMIC technology is recently progressing at a rapid rate and is now being applied in communications systems. However, there remain few practical applications. This is mainly due to the high cost of conventional mmics because of the small market size and specialized needs. This paper introduces three new technical approaches that overcome the problems: uniplanar mmic, line unified fet^lufet), and multilayer mmic. Concepts and several examples of these technologies are described. It is shown that these technologies are effective not only for cost reduction but also for increased performance. In addition, one example of system application is described.     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.     

Identifying rotation and oscillation in surface tension measurement using an oscillating droplet method

We proposed a new approach to identify the frequencies of droplet rotation and m=±2 oscillation that degrade the accuracy of surface tension measurement by an oscillating droplet method. Frequencies of droplet rotation and m=±2 oscillation can be identified by a phase unwrapping analysis of time dependence of the deflection angle for the maximum diameter of the droplet image observed from above. The present method was validated, using test data with given frequencies. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(7): 421–430, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20214     

Metallic Glass as a Mechanical Material for Microscanners

Microelectromechanical system (MEMS) actuators essentially have movable silicon structures where the mechanical motion can be activated electronically. The microscanner is one of the most successfully commercialized MEMS devices which are widely used for collecting optical information, manipulating light, and displaying images. While silicon is abundant, it is also brittle and stiff and when microprocessed, defects are not uncommon. These defects result in weakness under torsional stress and this has been the key factor limiting the scanning performance of the microscanner. Here a metallic glass (MG)‐based microscanner is reported with MG as the material for the moving torsion bars. The low elastic modulus, high fracture toughness, and high strength of MG offers, for the first time, an ultralarge rotating angle of 146° with power consumption lowered to the microwatt range, and a smaller driving force and better actuation performance, than conventional single crystal silicon and polycrystalline silicon. The high spatial resolution and large scanning field of the MG‐based microscanner are demonstrated in the tomographic imaging of a human finger. This development of an MG‐based MEMS possibly opens a new field of low‐powered MEMS devices with extreme actuation and enhanced sensing.     

Liquid phase synthesis of ZnO microrods highly oriented on the hexagonal ZnO sheets

We have successfully synthesized zinc oxide microrods perpendicularly oriented on hexagonal ZnO sheets by a simple heat treatment approach using LDH (layered double hydroxide) precursor in an aqueous solution. The synthesized ZnO microrods have an average diameter of 500 nm and length of 2–3 μm, and form highly-oriented array. In this work, the effect of heating temperature and time on morphology and orientation of ZnO microrods was studied experimentally and the formation mechanism was discussed in detail. Transformation from hexagonal precursor to ZnO microrods can be attributed to dissolution and re-precipitation of the precursor, which should be caused by its thermal unstability under heating temperature.     

Local electrical modification of a conductivity-switching polyimide film formed by molecular layer deposition

The electrical modification of a conductivity-switching polyimide film via molecular layer deposition (MLD) is studied for ultrahigh density data storage based on a scanning probe microscope (SPM). A PMDA-ODA (PMDA = 1, 2, 3, 5-benzenetetracarboxylic anhydride, ODA = 4, 4-oxydianiline) film as a recording medium is uniformly formed from a self-assembled monolayer on a Au surface by MLD. It is demonstrated that the conductivity of the film can be changed by applying a voltage between a SPM probe and the film. This conductivity-switching phenomenon is discussed by the molecular orbital approach and considered to be caused by the charge transfer effect or carrier trapping effect of PMDA-ODA.     

A Fail-safe Logic Operator Using an Insulated Planar Transformer

A fail-safe logic circuit must switch the output signal to the logical value “0” when an operation circuit fails. A transformer has such favorable characteristics for fail-safe logic circuits as only the magnetic flux change is transmitted and a superposition of magnetic flux is realized. Thus those characteristics arc applied to a failsafe logic operator. A new fail-safe logic operator using an insulated planar transformer was developed for a fail-safe majority operation and a fail-safe interlocking. In this paper, the principle, structure, design and fundamental characteristics of the new fail-safe logic operator are described.     

Design for 2-D error feedback networks with identical coefficient sets

In realization of recursive digital filters with fixed point arithmetic, an error caused by roundoff arises. It is known that the level of the roundoff noise of an IIR filter tends to be high when the poles are close to the unit circle. Error feedback (EF) is an effective method to reduce the roundoff noise. It is desirable to design an EF network using as few parameters as possible in order to keep computational costs low. In this paper, we propose a method for designing a 2D EF network with identical coefficient sets. That is, the EF coefficients are divided into several subsets such that all the elements within each set have the same absolute value. In order to optimize the coefficient sets, we propose an algorithm by using the genetic algorithm. In the numerical example, we demonstrate the effectiveness of the proposed method.