Counter-doped MOSFETs of 4H-SiC

In this paper, we investigate the effect of counter-doping of nitrogen at the channel region of epitaxial n-channel 4H-SiC MOSFETs on the channel mobility and the threshold voltage. From this study, we have found that the channel mobility steeply improves as the nitrogen dose increases. At a dose of 2× or 2.5×10¹² cm^-2 the enhancement MOSFET has achieved an effective channel mobility of 20 cm²/Vs or a field effect mobility of 38 cm²/Vs at a peak     

Co41Ni33Al26合金的再结晶、马氏体相变和铁磁特性

研究了Co41Ni33Al26铁磁性形状记忆合金的再结晶行为和组织变化规律,采用振动磁力计（VSM）和示差热分析仪（DSC）分析了合金磁性和马氏体相变特点。结果表明,经43．65％的大压下量冷轧变形的Co41Ni33Al26合金在低于1000℃发生再结晶,随着淬火温度的升高,合金中β相体积分数不断增加。冷轧组织中在β／γ相界面上有很多微裂纹,这是由于两相变形不协调而形成的,微裂纹的形成有利于合金的塑性变形,在高于1200℃处理时微裂纹消失,表现出“自愈合”能力。该合金的马氏体相变温度和居里点都随着淬火温度的升高而升高,居里点始终高于马氏体相变温度,且马氏体相的磁晶各向异性高于β母相的,说明该合金是很好的铁磁性形状记忆合金的候选材料。     

Discontinuous coarsening of the lamellar structure of γ-TiAl-based intermetallic alloys and its control

Discontinuous coarsening (DC) of the primary lamellar structure (PLS) occurring at lamellar colony boundaries (LCBs) and in surface layers of various Ti-(40 to 45) at. pct Al binary and Ti-46 at. pct Al-X (X=Si and C) ternary alloys was systematically investigated by using optical microscopy and scanning and transmission electron microscopy. The compositions of the α ₂ and γ phases in the primary lamellar structure were estimated based on the weight fractions of the two phases, determined by X-ray diffraction. When the solution-treated Ti-(40 to 45) at. pct Al binary alloys were subsequently soaked at 1000 °C, the primary lamellae in the Ti-40 at. pct Al alloy were the most stable, while those in the Ti-44 at. pct Al were the most unstable. Both the thermodynamic analysis and experimental results confirm that the driving force of the coarsening is mainly derived from the reduction of the chemical free energy (i.e., out-of-equilibrium chemical composition) and the interfacial energy of primary lamellae, whereas the coarsening resistance is mainly from the increase of the elastic strain energy of lamellar interfaces and the surrounding during coarsening. It is found that Si has an exceptional ability to hinder the coarsening of the primary lamellar structure at high temperatures, but the precise mechanism for this improvement is uncertain now. Based on this study, a proposal is finally addressed to improve the thermal stability of the primary lamellar structure of titanium aluminides.     

Measurement of partial specific thickness (net thickness) of critical-point-dried cultured fibroblast by energy analysis

The relative specimen thickness obtained with an energy analyser is one of the most important parameters in electron microscopy. It has been made clear that this parameter can be applied not only to inorganic specimens, but also to organic and biological specimens. Moreover, the partial specific thickness of a critical-point-dried cultured fibroblast, that is, a net thickness converted in terms of Epon, was calculated from the relative specimen thickness. The partial specific thickness of each domain of the critical-point-dried cultured fibroblast is : CC 0.05 μm, PE 0.14 μm, ED 0.32 μm and PN 0.54 μm. As a result, it is suggested that 27% of the volume of this specimen consists of biological materials.     

Fluoride-based erbium-doped fiber amplifier with inherently flat gain spectrum

We successfully developed a fluoride-based Er/sup 3+/-doped fiber amplifier (F-EDFA). An average signal gain of 26 dB was achieved for 8 channel wavelength division multiplexed (WDM) signals in the 1532-1560 nm wavelength region with a gain excursion of less than 1.5 dB at an input signal power of -20 dBm per channel. Furthermore, we studied the amplification characteristics of the F-EDFA for WDM signals. The following experimental results were obtained. (1) For an 8-channel WDM signal in the 1532 to 1560 nm wavelength region, the gain excursion between channels can be suppressed to within 1.5 dB. However, the wavelength region allowing a gain excursion of 1.5 dB, is between 1536-1560 nm for the silica-based Er/sup 3+/-doped fiber amplifier. (2) F-EDFAs have a flat gain region between 1534-1542 nm. The gain excursion of this region is less than 0.2 dB for WDM signals.     

Mechanical properties and microstructure of centrifugally compacted alumina and hot-isostatically-pressed alumina

High purity alumina powder was compacted under a high centrifugal force. Mechanical properties of the sintered body were studied by the three-point bending test at room temperature and by the compressive test at elevated temperatures. Comparison was made with hot-isostatically-pressed (HIP) alumina. The room-temperature flexural strength of the centrifugally compacted (CC) alumina was found to be 1330 MPa compared with 585 MPa of the HIP alumina. The difference in the room-temperature strength was attributed to the presence of the amorphous phase along the grain boundaries of the HIP alumina caused by the segregation of carbon and sulfur during HIP. A large ductility was observed above 1473 K in the CC alumina and above 1573 K in the HIP alumina. High-temperature ductility was lost in the HIP alumina at 1773 K where the amorphous grain-boundary phase was considered to be melted.     

Creep mechanism in Fe-1.8 At. Pct Mo alloy at high temperatures

High temperature creep of Fe-1.8Mo alloy, the stress exponent,n, of which is about 4, has been studied to check whether then value can be a good indication of the creep mechanism or not. Creep tests were carried out at 1124 K under 5.9 to 39.2 MPa. After sudden stress increments during the steady-state creep, inverse-type transient creep curves were obtained with no instantaneous permanent strain. Mean internal stresses were determined by stress-transient dip-tests using a back extrapolation technique. The mean internal stress was obviously smaller than the applied stress. These results indicate that creep deformation of Fe-1.8Mo alloy under the present conditions is controlled by the viscous glide motion of dislocations, thoughn is not close to 3. Steady-state creep rates as well as the value ofn calculated from the Orowan-type equation using experimentally obtained values for every parameter, are in reasonable agreement with the observed ones. These findings suggest that classification of creep behavior according to then value is not appropriate in some cases for discussing mechanisms of high temperature creep. Formerly was a Graduate Student, Tohoku University.