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GaN micro-pyramids were fabricated on n-type CaN buffer layer/c-plane sapphire wafer. In order to understand the growing ZnO on GaN {1–1 0 1} facets, ZnO nanostructures on GaN micro-pyramids with and without Au catalyst were synthesized by chemical vapor deposition (CVD). As-prepared ZnO nanostructures were characterized by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). ZnO nano-sheets on the micro-pyramids without Au catalyst have a terrace-like structure, which is explained by vapor–solid mechanism. ZnO nanowires with a gold particle on the top grow on micro-pyramids with Au catalyst, which is explained by vapor–liquid–solid mechanism. Nanowire bridges crosslinking two adjacent micro-pyramids are frequently observed, which demonstrates the capability to develop self-organizing electrical interconnects and nanoscale devices. The diameters of the resulting ZnO nanowires are in the range of 40–100 nm with typical length about 10 μm.

The effects of substrate temperature on the resistivity and transmittance of ZAO thin films prepared by DC magnetron reactive sputtering have been investigated. The properties of the samples have been analyzed through Hall effect, X-ray diffraction and SEM. The results show that carrier concentration, Hall mobility and crystallinity of the films depend obviously on the deposition temperature. The film deposited at the range 200-250°C has lower resistivity and higher transmittance.

Cu0.62Zn0.38 brass foil was heated at temperatures of 400–700 °C in flowing N2–5%O2 at a pressure of 1 atm. for 1–24 h. The oxidized specimens were characterized with a scanning electron microscope, an X-ray diffractometer and a transmission electron microscope. The results show that hexagon ZnO nanowires and nanowalls grew on convoluted oxide scales when brass foils were oxidized at 500 and 600 °C. Thermodynamics of forming ZnO is analyzed based on oxidation theory of an alloy. Pilling–Bedworth ratio of Cu–Zn alloy is calculated based on the volume differences between the formed oxide and the consumed metal. The growth stresses caused by Pilling–Bedworth ratio of the alloy and stress relief of oxide scale at different oxidation temperature are analyzed. The mechanism of forming nanostructural ZnO on the convoluted oxide scales is explained by the change in the growth stresses and stress relief of oxide scale during thermal oxidation.

This paper is the second part of our study on the advanced energy storage system using H 2 O–LiBr as working fluid. In the first part, the system working principle has been introduced, and the system dynamic models in the operation process have also been developed. Based on the previous research, this paper focuses on the numerical simulation to investigate the system dynamic characteristics and performances when it works to provide combined air-conditioning and hot water supplying for a hotel located near by Yangzi River in China. The system operation conditions were set as follows: the outdoor temperature was between 29 °C and 38 °C, the maximum air-conditioning load was 1450 kW, the total air-conditioning capacity was 19,890 kWh and the 50 °C hot water capacity for showering was 20 tons which needed heat about 721 kWh on a given day. Under these conditions, the system operation characteristics were simulated under the full- and partial-storage strategies. The simulation results predicted the dynamic characteristics and performances of the system, including the temperature and concentration of the working fluid, the mass and energy in the storage tanks, the compressor intake mass or volume flow rate, discharge pressure, compression ratio, power and consumption work, the heat loads of heat exchanger devices in the system and so on. The results also showed that the integrated coefficient of performances (COP int ) of the system were 3.09 and 3.26, respectively, under the two storage strategies while the isentropic efficiency of water vapor compressor was 0.6. The simulation results are very helpful for understanding and evaluating the system as well as for system design, operation and control, and device design or selection in detail.

The attraction force between the AFM tip and the surface of sputtered dielectric thin films (SiO2 and ZrO2) was measured with atomic force microscope (AFM) by applying DC-bias between the AFM tip and the n-Si substrate. Under 0 electric field, there exists van der Waals interaction between the AFM tip and the surface of dielectric films. When DC voltages are applied, the attraction force increases obviously for thin SiO2 (5.2 nm) and ZrO2 (6.8 nm) films due to the columbic interaction between them. A parallel-plate model has been developed to evaluate the ideal columbic tip-surface force for SiO2 and ZrO2 films. Contrary to the calculation result, the columbic force for ZrO2 film (6.8 nm) is lower than that for SiO2 film (5.2 nm), indicating the poor dielectric properties of the ZrO2 film. The poor dielectric properties of ZrO2 film should be due to the interfacial SiOx-containing layer formed between ZrO2 and Si, supporting the conclusion reached in the literature that the interfacial SiOx-containing layer can deleteriously influence the dielectric properties of high-k films.

The metallization of wire bonding pads on Si-based integrated circuits (ICs) contains Ti, TiN, and Al layers with vertical W-plugs located through the Ti and TiN layers. One percent Si-Al wire (32 µm in diameter) was bonded on the pads by an ultrasonic transducer using a wire bonding machine. Peeling failures occurred during the ultrasonic bonding process. The peeling fractures were examined using a scanning electron microscope (SEM) with an energy-dispersive spectroscopy (EDS) system. The results showed that bonds peeled off from the interface between the Al layer and the top surface of the W-plugs or from the interface between the Si-base and the bottom surface of the W-plugs. The distribution of W-plugs also affected the bond peeling from the top or bottom surfaces of the W-plugs. Mechanisms giving rise to the peeling failure of bonds were analyzed based on the acoustic impedance of materials, which determined the amount of ultrasonic energy transmitted from one material to another. Two differ...

Two types of ultrasonic transducers: full ceramics (lead zirconate titanate, PZT) and composite (PZT embedded in a polymer) transducers, were used for wire bonding. Al wire is 32 μm in diameter and bond pads contain Au/Ni/Cu trilayer coating on PCB boards. Bonding Al wire on the pads was processed on three different power levels and with various bond times at each bond power to compare the bonding performance of the two types of transducers. The actual bond areas were measured after the Al wire had been removed in a base solution. Bonding kinetics was analyzed based on actual bond areas. Pull strength test was used to examine bonding quality. The fractured bonds were examined using a scanning electron microscope. The results show that the bonding rate by the full ceramic transducer is faster than that by the composite transducer in the initial stage. A maximum bond strength is attained after a certain bond time which is different depending on the bond power. This maximum bond strength produced by the composite transducer occurs at longer bonding time. The widths of the bonds produced by the composite transducer are significantly narrower than those of the bonds produced by the full ceramic transducer. The reduced bond width gives rise to higher bond strength.

Lead zirconate titanate rings were subjected to different mechanical stress applied by bolt clamping. The piezoelectric and elastic coefficients, the relative permittivity and the electromechanical coupling factor of the compressed rings were evaluated from the impedance and phase spectra using a commercial package “Piezoelectric Resonance Analysis Program” (PRAP). The results show that the piezoelectric coefficient e 33 , elastic coefficient c 33 D and electromechanical coupling factor k t decreased, while the relative permittivity e 33 S / e 0 increased with the increase in mechanical stress. The changes of the material parameters of the compressed rings are understood from the movements of domain walls upon the application of different torques.

A high electric field at different frequencies (near resonance) was applied on a piezoelectric vibrator. Current, phase between current and driven voltage, and sample temperature were measured during the operation. The results show that if an initial current in a specimen is large enough to increase sample temperature, the impedance spectra of the specimen will shift to low frequency direction during the operation. This results in the change in current, according to the shifted impedance spectra. The operation of a piezoelectric vibrator at slightly less resonance frequency will damage the vibrator more seriously than that at resonance frequency or at slightly higher resonance frequency due to the shift of impedance spectra. When a piezoelectric vibrator is operated at the frequency far away from resonance frequency, the current is not enough to increase sample temperature. In this case, the operation is safe.

Initiation and propagation of cracks in lead zirconate titanate (PZT) piezoelectric rings under a non-uniform mechanical loading were studied. The PZT ring was sandwiched between two pieces of metals and then compressed by a torque. Bolt clamping produced a non-uniform external stress on the PZT ring and caused various degree of depoling at different positions of the ring. A large torque also initiated cracking and breaking in the ring. Fracture features of the broken PZT ring were observed using scanning electron microscopy (SEM). Fracture toughness at the inner part of the ring changed significantly due to 90° domain rotation after a large torque had been applied. The ratio between the fracture toughness along the thickness direction and the fracture toughness along the radial direction varied from >1 to

The formation and mechanisms of the texture growth of boride phases during superplastic boronizing were studied in comparison with conventional boronizing. The texture degree was quantitatively determined by using X-ray diffraction with Lotgering method. The microstructures and distributions of the alloy elements were studied by using SEM and electron probe microanalysis. Microhardness tests across the boride layers were also performed. The results indicated that the superplastic boronizing retarded the formation of the high boron containing boride phases and reduced the growth texture of the borides. Compared with the conventional boronizing, the FeB growth texture was eliminated and Fe2B growth texture was reduced significantly with the superplastic boronizing. The superplastic boronizing processes also suppressed the formation of the Si-rich zones which otherwise would form between the boride grains. The microhardness of the boride layer processed by the superplastic boronizing was more uniform than that produced by the conventional boronizing.

The isothermal oxidation behaviour of doped and undoped Fe–37 at% Al intermetallic compounds in an ambient atmosphere over the temperature range of 1000–1200°C was studied. The oxidation products were identified by X-ray diffraction (XRD). Characterisation of the specimens after oxidation was conducted using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The rate constants of the isothermal oxidation were determined using three methods. The effective diffusion coefficients for the oxidation of doped and undoped Fe–37Al are discussed based on oxide grain size and the effects of reactive elements in lattice and grain boundaries. The effects of reactive elements on the isothermal oxidation kinetics of Fe–37Al were analysed based on oxide morphologies and microstructures.

Superplastic boronizing is a new processing technology that combines boronizing with superplastic deformation. This process not only has a much faster boronizing rate compared with the conventional boronizing method, but also produces boronized layers with improved mechanical properties. The present project studies the mechanical properties of a low-alloy steel (0.9C1Si1CrFe) after superplastic boronizing treatment. The results indicate that superplastic boronizing has improved the fracture strength of the specimens by 8%, the toughness by 18% and the maximum flexure by 15%, compared with the conventional boronizing process. Microstructural and microcompositional changes were observed which are believed to effect the mechanical-property improvement. Superplastic boronizing has wide potential applications in the surface modification on steels, and it can be used to study the mechanism of superplastic deformation.

Superplasticity has been developed rapidly since the 1960`s. Superplasticity and superplastic deformation technique of steel and ferrous alloys offer a new method of forming complex parts for industrial applications, such as dies and gears. On the other hand, boronizing has long been used to improve the surface properties of dies and tools because boride has high hardness, good wear resistance, and good corrosion and oxidation resistance. Superplastic boronizing, a new technique, is the processes that combines boronizing with superplastic deformation. Because two processes become one, energy and time can be saved. In the present paper, the superplastic boronizing processes for commercial 0.9C-1Si-1Cr-Fe and 1C-1Cr-Fe steels are described first. Then, the microstructure and properties of specimens produced by using superplastic and conventional boronizing are compared. Finally, a physical model for superplastic boronizing processes is suggested.

The power bipolar junction transistor (PBJT) is investigated and modeled. Particular interest is concentrated on the injection charge in the collector layer that dominates the large-signal characteristics of the device. Based on the semiconductor physics, ordinary differential equations describing the injection charge are derived. These equations take into account the recombination, charging, and discharging processes in the collector layer. A network model for the PBJT is derived by adding these equations to a standard model. This model is implemented in the IG-SPICE language. The static behavior, such as the quasi-saturation, and the dynamic behavior, including turn-off under the strong drive condition, can be simulated and analyzed. The simulation correlates well with the measurement. >

An integrated two-phase anaerobic reactor of 4.5 m is introduced. It is used to treat the piggery wastewater. The performance of reactor is monitored and analyzed including the influent and effluent of total suspended solid (TSS), volatile suspended solid, (VSS), total nitrogen (TN), total phosphor (TP), CODcr, BOD and gas production. Experiment results shows that the optimal organic loading rate (OLR) is 10kg-VSS/m3 day in the first-phase and 1.5kg-VSS/m3-day in the second-phase. The optimal hydraulic retention time (HRT) is 2 days in fires-phase and 13 days in second-phase. The maximum gas production rate of VSS is about 1 m3/kg-VSS-day.

A model of a power MOSFET has been improved and implemented in SPICE. A method for parameter extraction from electrical measurements has been developed. The model is simple and accurate, and the simulation results show good agreement with the measurements. The switching behavior of the MOSFETs has been simulated and analyzed, and the parasitic oscillation in parallel circuits has been investigated. A way to avoid this undesirable effect is proposed and proved. The development of an electrical analysis model for the p-i-n power diode is reported. The internal processes during switching have been investigated using physical device simulation, and a one-dimensional solution has been obtained. >

Ring-shaped lead zirconate titanate (PZT) piezoelectric vibrators were subjected to non-uniform mechanical stress applied by bolt clamping. The effect of mechanical stress on the effective electromechanical coupling factor (keff) and mechanical quality factor (Qm) of the thickness and wall thickness modes was studied by an equivalent electric circuit analysis. The initiation and propagation of cracks under mechanical stress were also discussed based on the resonance method and the indentation technique. keff for both the thickness and wall thickness modes decreased with increase in mechanical stress due to de-poling of the PZT. Qm of the thickness mode dropped sharply with increase in mechanical stress while Qm of the wall thickness mode remained almost unchange. Existence of microcracks in a PZT vibrator can be detected by the occurrence of spurious vibrations at the wall thickness mode in the electrical impedance vs. frequency spectra.

The structural properties of carbon clusters (C n , n=2-60) are studied using tight-binding moleculardynamics simulations. The low-energy ground-state configurations of the clusters are obtained by annealing and compressing n carbon atoms (n=2-60) from the gas phase at high temperatures (≥6000 K). We observed a transition from one-dimensional linear and cyclic structures to two-dimensional cage structures as the number of atoms in the cluster increases beyond n=20