Papers by Keyword: Temperature Dependence

Abstract: The analysis of Cu ETP of a component of electric motors manufactured by WEG is presented. The work included three main tasks: metallographic analyses at the micro and macro levels; mechanical testing; scanning electron microscopy observations. The objective was the evaluation of the state of bars material before and after service. It was found that material in both conditions presents similar microstructures. This indicates that, despite the rotor working at temperatures above 300°C, no grain recrystallization can be identified. It was verified that the copper bar base material presents higher hardness values of than the copper ring. A decrease of yield and rupture stresses as the temperature increases was observed during tensile tests at different temperatures. During testing, a fatigue life of 10⁷ cycles for a remote stress of approximately 134MPa is estimated. It can be concluded that the material after and before service presents different properties, the first one presenting lower strength. This behavior is reflected in lower hardness, yield and rupture stress of the material taken from the fractured rotor bars. This observation can be a result of the high temperature (above 300°C) that is present in the rotor during each start.

Abstract: By measuring the angular dependence of ferromagnetic resonance field at room and low temperatures, it is demonstrated that the magnitude of magnetic field applied during magnetron deposition of Ta/F/AF/Ta structures, where F=Co, NiFe and AF=FeMn and IrMn, influences the uniaxial and unidirectional anisotropy, magnetization and the exchange bias blocking temperature. The deposition field effects on the bilayer structure are compared with the effects on a similar structure, but without antiferromagnetic layer. The exchange bias blocking temperature of investigated structures is found to be significantly lower than the Néel temperature of a bulk antiferromagnet. The origin of the observed effects is shortly discussed.

Abstract: Using the method of angular dependence of ferromagnetic resonance field the magnetic properties of Si/SiO₂/Cu/Co/FeMn/Cu and Si/SiO₂/Cu/Co/Cu/FeMn/Cu structures were investigated. The layer deposition was carried out by magnetron sputtering in absence of an external magnetic field. It was established that thermal annealing with further cooling down in presence of a magnetic field can generate an exchange bias at anneal temperature significantly below the bulk antiferromagnetic Néel temperature. It was also shown that a thin interlayer between ferromagnetic and antiferromagnetic layers reduces the exchange bias effect at low anneal temperatures, however, makes this effect more stable at high annealing temperatures.

Abstract: Integration of patterned ballast resistance into the anode of SiC PiNs is a solution to the dilemma of negative dV_f /dT for such diodes. In fabricated 4H-SiC PiN diodes, we demonstrate a cross-over from negative to positive temperature coefficient for current densities as low as 80 A/cm². Adjusting the percentage of the patterned anode area, the positive or neutral dV_f /dT can be achieved over a wide current-density range without substantial penalty in the forward voltage drop. This characteristic is crucial for high-power SiC packages with ganged-parallel rectifier arrays.

Abstract: The effects of temperature, stress level and hygrothermal aging on the creep-recovery behaviors of anisotropic conductive adhesive film (ACF) were investigated experimentally using a dynamic mechanical analyzer (DMA). It is found that the initial strains, instantaneous strains, and creep or recovery rates increase with increasing temperature，however decrease with increasing hygrothermal aging time. The change of creep or recovery rates at low temperature is apparent, however the creep or recovery rates increase obviously at temperatures above 25 oC with increasing stress level. For the hygrothermal aged ACF, the time to reach steady creep stage or steady recovery stage is reduced significantly compared with the unaged sample. The strain jumps at instantaneous loading decrease visibly and the strain jumps at instantaneous unloading decrease slightly with increasing aging time. And the strain jumps at instantaneous loading and unloading increase with increasing stress level for the unaged and aged ACFs.

Abstract: One-dimensional (1D) nanowire is one of the most important components for nanosized electronic devices’ development, sensors. Eu3+-doped lanthanum phosphate nanowire has been synthesized via hydrothermal method. The sample is characterized using XRD and SEM; SEM images show the diameter of LaPO4:Eu3+ nanowires before heat treatment is about 10 nm. After sinter, the LaPO4:Eu3+ nanowire becomes particles. The particles grow up and the luminescence intensity becomes lower with the sintering temperature going higher, while the life time of 5D0→7F1 transition is longer. It is suppose that the perfect lattice is not benefit to the dopant ions into.

Abstract: In order to reveal the temperature dependence of a touch mode capacitive pressure sensor, temperature dependence of material parameters of the sense have been studied. Using Finite Element Method (FEM) to simulate and solve capacitance, the results show that the relation of capacitance and temperature is almost linear in touch state of the sensor. At the same time, temperature sensitivities under different pressure are slight difference, which are 0.0056pF/K and 0.0040pF/K, respectively. Therefore, the high-temperature performance of the sensor is greatly outstanding.

Abstract: An environmentally friendly synthesis was developed to fabricate aqueous CdTe quantum dots (QDs) using thilglycolic acid (TGA) as a capping agent. Optimal preparation conditions including pH (11.2) and TGA/Cd molar ratio (1.5:1) resulted in CdTe QDs with high photoluminescence (PL) quantum yield up to 56%. The TGA-capped CdTe QDs exhibited tunable PL from green to red. Lifetime measurement indicated that the average lifetime of the TGA-capped QDs increased with increasing their sizes (27.5 and 37.2 ns for the QDs with PL peak wavelength of 607 and 636 nm, respectively). The PL of the QDs revealed the dependence of temperature, in which the QDs exhibited a red-shifted PL peak with increasing temperature. Such PL behavior depended strongly on the QD sizes.

Abstract: In this paper, We use a novel principle to detect acceleration and report how I-V characteristics and piezoresistance coefficient of AlGaN/GaN HEFT-micro-accelerometer are affected by setting different temperatures. It is shown that saturation current of device would go down if the temperature goes up, which is about 0.028mA/°C, based on the research. However, the device can work well at the temperature range of -50°C to 50°C, which indicates that it can work safely in the larger temperature range.

Abstract: Four series of thin films have been deposited as the precursory sources of Zn(CH3COO)2, Mg(CH3COO)2, NH4CH3COO and AlCl3 aqueous solutions using ultrasonic spray pyrolysis (USP) method. The crystalline structure, morphology images, electrical, optical properties of the films are characterized by x-ray diffraction (XRD), field emission-scan electron image (FE-SEM), Hall-effect measurement and photoluminescence (PL). From the XRD patterns and SEM images, we can see that all the films present good crystallinity and surface uniformity. Hall-effect measurement results indicate that ZnO is n-type, while N-Al codoped ZnO and N-Al codoped Zn1-xMgxO exhibit p-type conduction. Temperature dependent of electrical measurement is carried out from 300K to 500K, then the conductive mechanism and carriers scattering are analysed. Furthermore, the photoluminescence peak of Zn1-xMgxO is tuned into shorten wavelength than pure ZnO (λ＝379－352＝27nm), and also the same phenomenon of the p-type Zn1-xMgxO film exhibits blue-shifted behavior from 378nm to 356nm compared with p-type ZnO film (λ＝378－356＝21nm). In other word, the p-type Zn1-xMgxO film shifts to a shorter wavelength of 356 nm while maintaining excellent electrical performances.