First-principles study of A-site substitution in ferroelectric bismuth titanate

We employ density functional theory to investigate the effect of A-site rare earth substitution on the point defect formation in bismuth titanate (BIT) in the dilute substitution limit. Despite previous claims that the formation energy of neutral oxygen vacancies in La-substituted BIT (BLT) is higher than in pure BIT, our calculations show that this is only true for four out of the six distinct oxygen sites. Of these four sites, in two the difference is <0.1 eV while in the other two the difference is ~0.25 eV. In the case of +2 charged oxygen vacancies, in only two of the six distinct oxygen sites is the formation energy of the oxygen vacancy higher in BLT than in BIT, where they differ by ~0.14 eV. These results do not support the traditional explanation for the fatigue-free characteristic of BLT, which states that La substitution might avoid the ferroelectric fatigue of BIT by simply suppressing the formation of oxygen vacancies.     

Operation of vehicles in AGV system and method for analyzing operation

It is important to discuss the behavior of traffic at merging sections for the design and realization of an automated guided vehicle system (AGVS). In this study, we deal with a merging section of the AGVS by considering the time limit for the merging of vehicles. Near the merging section, the traffic flow in one direction forms a queue to avoid collisions between vehicles. We present an improvement of the control strategy proposed in previous research. However, since it is difficult to analyze the mathematical model of the merging section, analysis can be performed only for the case in which the time limit is set to the least values. We also propose a method for analyzing the model for an arbitrary time limit by using a linear recurrence relation. We discuss quantitatively the influence of the time limit on the average queue length and the detour rate. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(1): 56–68, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21190     

Design perspective against random dopant fluctuation and process variation for scaling multi-gate devices

Multi-gate devices such as DG (Double Gate), SG (Single Gate) and tri-gate, are extensively examined and expected to be one of the promising device structures beyond bulk MOSFETs. We demonstrate the basic characteristics considering random dopant fluctuation for novel device structures and study the sensitivity against process variations. Moreover, we build a 6T-SRAM cell considering random dopant in the channel and calculate the Static Noise Margin (SNM) directly from hp45 down to hp22.     

New Ultraviolet Photodetector Based on Individual Nb2O5 Nanobelts

Although human eyes are quite insensitive to ultraviolet (UV) light, most of the longer wavelength UV light (the UV‐A band between 320 and 400 nm) does reach the earth surface and after prolonged exposure, the radiation can cause health concerns especially skin cancer. Therefore, it is extremely important to explore ways to effectively monitor the radiation. Herein we report for the first time a new high‐performance UV photodetector made of an individual Nb₂O₅ nanobelt. Quasi‐aligned Nb₂O₅ nanobelts 100–500 nm wide and 2–10 μm long were synthesized using a hydrothermal treatment of a niobium foil in a KOH solution followed by proton exchange and calcination treatment. A nanostructured photodetector was constructed from an individual Nb₂O₅ nanobelt and its optoelectronic properties were evaluated. The detector exhibited linear photocurrent characteristics, excellent light selectivity, and high external quantum‐efficiency (EQE) of 6070%. Long‐term stability of the photocurrent over a period of 2500 s at an applied voltage of 1.0 V was achieved. The photodetector performance was further enhanced by improving the crystallinity and eliminating the defects in the Nb₂O₅ nanobelt crystals. These excellent optoelectronic properties demonstrate that Nb₂O₅ nanobelts are suitable for visible‐blind UV‐light sensors and optoelectronic circuits, especially those operating in the UV‐A range.     

Towards Thermoconductive,Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers

Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20‐fold thermal conductivity improvement in BNNT‐containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT‐loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat‐releasing materials.     

多孔硅层湿法腐蚀现象的研究

阳极氧化法制备的多孔硅层分别经 1% HF、 1% NH3 / H2 O2 和 0 .0 5 % Na OH三种溶液在室温下进行湿法腐蚀 ,并用傅里叶变换红外光谱 (FTIR)和扫描电子显微镜 (SEM)对其变化进行了研究。腐蚀后多孔硅的表面形貌出现明显的刻蚀现象。红外吸收光谱表明 ,在用 1% NH3 / H2 O2 溶液腐蚀时 ,多孔硅层中 Si- O键和 Si- H键的强度增加 ,H- O键的强度下降 ;用 1% HF溶液和 0 .0 5 % Na OH溶液的腐蚀结果正好相反。 0 .0 5 %Na OH溶液对多孔硅层的腐蚀现象类似于强碱性溶液对单晶硅腐蚀表现出的各向异性 ,对多孔硅层厚度的腐蚀速度比 1% HF溶液的高     

Synthetic Routes and Formation Mechanisms of Spherical Boron Nitride Nanoparticles

A new concept is proposed to explain the formation of spherical boron nitride (BN) nanoparticles synthesized by the chemical vapor deposition (CVD) reaction of trimethoxyborane (B(OMe)₃) with ammonia. The intermediate phases formed during the CVD under different reaction conditions are analyzed by X‐ray diffraction, electron microscopy, thermogravimetry, and spectroscopy techniques. The transition mechanism from an intermediate B(OMe)_3–xH_3–xN (x < 2) phase having single B? N bonds to the BN nanoparticles is elucidated. This particularly emphasizes the CVD temperature effect governing the conversion of the N? H···O? B hydrogen bonds in (OMe)₃B · NH₃ into the N? B bonds in B(OMe)_3–xH_3–xN. The spherical morphology strongly depends on the remnant impurity oxygen formed upon Me₂O group elimination in the intermediate. Two types of spherical BN nanoparticles primarily attractive for immediate commercialization (with C and H impurities at a level less than 1 wt %) are synthesized by the adjustment of experimental parameters: high oxygen‐containing (～6.3 wt %) BN spheres with a diameter of ～90 nm and a specific surface area of 26.8 m² g^?1; and low oxygen‐containing (<1 wt %) BN spheres with a diameter of ～30 nm and a surface area of 52.7 m² g^?1. Finally, the regarded synthetic techniques are fully optimized in the present work.     

Novel Electronic and Magnetic Properties of Two‐Dimensional Transition Metal Carbides and Nitrides

Layered MAX phases are exfoliated into 2D single layers and multilayers, so‐called MXenes. Using first‐principles calculations, the formation and electronic properties of various MXene systems, M₂C (M = Sc, Ti, V, Cr, Zr, Nb, Ta) and M₂N (M = Ti, Cr, Zr) with surfaces chemically functionalized by F, OH, and O groups, are examined. Upon appropriate surface functionalization, Sc₂C, Ti₂C, Zr₂C, and Hf₂C MXenes are expected to become semiconductors. It is also derived theoretically that functionalized Cr₂C and Cr₂N MXenes are magnetic. Thermoelectric calculations based on the Boltzmann theory imply that semiconducting MXenes attain very large Seebeck coefficients at low temperatures.     

极化合成孔径雷达及其应用

先进的对地观测卫星(即ALOS)在日本于2006年1月24日成功发射.在所携带的三个传感器中,L波段的相控阵合成孔径雷达(即PALSAR)能够使我们利用全极化的观测模式日夜对地球进行观测.尽管极化运行是实验性质的,但在世界上它首次为我们提供了星载的全极化数据.该文简单介绍ALOS卫星上的PALSAR系统、全极化数据的各种应用以及极化SAR图像分析结果.     

Degradation behavior in InGaAs/GaAs strained-quantum well lasers

Facet degradation mechanisms of a 980-nm InGaAs/GaAs strained-quantum well laser are analyzed by monitoring the optical-beam induced current. It is clarified that the behavior of defects around the facets govern the long-term stability as well as catastrophic-optical damage generation during operation.