Effect of Forming Pressure on the Internal Structure of Alumina Green Bodies Examined with Immersion Liquid Technique

Green bodies prepared by compaction of alumina granules were made transparent by an immersion liquid technique, and the internal structure was characterized with an optical microscope to study the effect of forming pressure on the internal structure. Clear images obtained by the technique provide more detailed information than other existing methods for structures ranging from one to tens of micrometers. Intergranular pores were present between unfractured granules. Their sizes and concentration tended to decrease with increasing forming pressure. However, pores were clearly present even in the green body prepared at 600 MPa. A rod- and needlelike feature was also found and was concluded to correspond to a high-density region. The significance of large pores and high-density regions on processing as well as the details of the technique is discussed.     

Optoelectronic devices towards monolithic integration

Starting from the present state-of-the-art of discrete devices up to the realization of monolithic semiconductor integrated prototypes, an overview of optoelectronic devices for telecommunications is given. Among discrete devices single frequency lasers, tunable and multi-sectionDFB lasers andPIN andAPD photodiode detectors are analysed, including the use of new technologies in progress for a second generation of devices. On the future perspective ofIBCN distribution networks, some economics of the hybrid and monolithic form of integration are attempted. Finally a short outline of the most recent achievements in monolithic integration is presented, taking into particular consideration the activities in this field byEEC ESPRIT andRACE programmes.     

The Effect of Polymer Optoelectronic Properties on the Performance of Multilayer Hybrid Polymer/TiO2 Solar Cells

We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO₂ and a conjugated polymer. Three different poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene) (MEH‐PPV)‐based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time‐of‐flight mobility measurements, and optical spectroscopy to characterize the exciton‐transport, charge‐transport, and light‐harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic‐device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO₂/polymer devices as a function of the fabrication route and device design. Including a dip‐coating step before spin‐coating the polymer leads to excellent polymer penetration into highly structured TiO₂ networks, as was confirmed through transient optical measurements of the photoinduced charge‐transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip‐coated and PEDOT:PSS layers produced a short‐circuit current density of about 1 mA cm^–2, a fill factor of 0.50, and an open‐circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm^–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %.     

Liquid crystalline polymers as additives to enhance the device properties of low molecular mass liquid crystals

Magnetic and electric fields have been used to determine the splay (k₁₁) and bend (k₃₃) elastic constants in a series of polymer/monomer liquid crystal solutions using the well known Freedericksz transition technique. Measurements have been carried out as a function of concentration and temperature. The polymer used was a smectogenic polysiloxane side chain liquid crystal with both cyanobiphenyl and benzoate ester side groups. The monomeric solvent was the nematogen 4-n-pentyl-4′-cyanobiphenyl. All of the solutions studied were nematogenic up to a concentration of 40% w/w. It has been shown that k₁₁, k₃₃ and $\text{k}{}_{33}\text{k}{}_{11}$ all decrease with increasing polymer concentration and that at high enough concentrations $\text{k}{}_{33}\text{k}{}_{11}$ tends to become independent of temperature. The implications of these results are discussed in terms of the performance of the most common liquid crystal display, i.e. the twisted nematic device.     

微密封真空微电子二极管

本文介绍了一种微密封真空微电子二极管的工艺及实验结果。     

同轴型光电器件的研究开发

本文简要地介绍了武汉电信器件公司正在研究开发的同轴型光电器件，新的器件的工艺与结构特点以及主要技术指标、使用前景。     

Cover Picture: Light‐Emitting Organic Solar Cells Based on a 3D Conjugated System with Internal Charge Transfer (Adv. Mater. 22/2006)

The cover image illustrates the dual photovoltaic and electroluminescence function of a single‐layer device based on a thienylenevinylene–triphenylamine with internal charge transfer (ICT), as reported by Cravino, Roncali, and co‐workers on p. 3033. The material forms an organic glass with isotropic electronic properties while ICT leads simultaneously to an extension of the photoresponse to the red and to an increase of the open circuit voltage. The use of an additional layer of C₆₀ further improves the photovoltaic. Images of the sun and moon courtesy NASA/JPL–Caltech.     

高精细数字会聚校正系统

数字会聚校正使1%的会聚精度提高到0.1%以上。本文叙述了数字会聚校正系统的设计要求,工作原理以及设计计算,给出了在投影电视上的试验结果,最后,指出了今后发展的方向。     

变频器的选型及配置要点

本文针对应用广泛的通用变频器，提出了在变频器选型和外围配置中需要注意的一些问题。     

Inside Front Cover: Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning (Adv. Mater. 6/2007)

Columnar liquid crystals (LCs) are found to spontaneously form homeotropically‐aligned films when deposited on surfaces fabricated via friction transfer of polytetrafluoroethylene. The inside cover schematically shows the film structure of a phthalocyanine derivative together with the corresponding X‐ray diffraction pattern (inset). The results, reported on p. 815 by Dmitri Ivanov and co‐workers, indicate that not only are the columns homeotropically oriented but also that they form a single monodomain of macroscopic size. These findings can have an important impact for fabrication of LC‐based organic solar cells.