Summary of HgCdTe 2D array technology in the U.K.

HgCdTe 2D arrays are needed in both medium (MW) and long (LW) wavebands for imaging, search, and track and guidance applications. Often the detector is the performance-limiting component in the system, and it is necessary to use detectors with very low excess noise and few defective pixels. Normally the detector is cooled sufficiently to freeze-out thermally generated leakage currents, so the main interest is to understand the mechanisms that determine the general detector performance and the cause of defective pixels. This paper describes the detector technology and the ion beam junction-forming process. The fundamental performance limits of homojunction HgCdTe technology and the doping levels needed to produce a detector with impact-ionization limited performance are discussed. Extensive studies have been made on defective pixels in long wavelength arrays and some technologies for reducing them are described here. Defective pixels have been found to be associated with material dislocations crossing the p-n junction and a model has been proposed for the noise-generating mechanism.     

Electronically scanned cmt detector array for the 8?14 ?m band

A cadmium-mercury-telluride photovoltaic hybrid array of 1024 elements is described. The device operates in the 8?14 ?m band and is electronically scanned by means of MOS silicon switches. An example of a `staring? image obtained with the device is shown.     

CO/sub 2/ laser processing of alumina (Al/sub 2/O/sub 3/) printed circuit board substrates

We report the results of an investigation of the laser-material interaction processes involved in laser drilling of alumina, through the use of an enhanced peak power (2.5 kW) CO/sub 2/ laser and novel temporal pulse formats. Peak power was varied from 30 W to 2 kW for pulses of constant energy to observe the effect produced on scribe depth. High-speed videography of hole formation has been combined with microscopic analysis to investigate the key processes involved in laser processing of alumina. Plasma screening was observed for short, high peak power laser pulses, and optimal scribing was achieved in the weakly plasma absorbing regime. A new processing technique for scribing alumina has been developed, which exploits the fast response of the laser to produce novel temporal pulse shapes, which can be modified to generate cleaner holes. Scribe speeds of up to 280 mm/spl middot/s/sup -1/ were obtained for scribe holes >200 /spl mu/m deep and 150 /spl mu/m apart, with no material plugging the hole, in 0.635-mm-thick 96% alumina.     

Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures

TiO₂ nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO₂ nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO₂ nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO₂ nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons.     

A Protein-Adsorbent Hydrogel with Tunable Stiffness for Tissue Culture Demonstrates Matrix-Dependent Stiffness Responses

Although tissue culture plastic has been widely employed for cell culture, the rigidity of plastic is not physiologic. Softer hydrogels used to culture cells have not been widely adopted in part because coupling chemistries are required to covalently capture extracellular matrix (ECM) proteins and support cell adhesion. To create an in vitro system with tunable stiffnesses that readily adsorbs ECM proteins for cell culture, a novel hydrophobic hydrogel system is presented via chemically converting hydroxyl residues on the dextran backbone to methacrylate groups, thereby transforming non-protein adhesive, hydrophilic dextran to highly protein adsorbent substrates. Increasing methacrylate functionality increases the hydrophobicity in the resulting hydrogels and enhances ECM protein adsorption without additional chemical reactions. These hydrophobic hydrogels permit facile and tunable modulation of substrate stiffness independent of hydrophobicity or ECM coatings. Using this approach, it is shown that substrate stiffness and ECM adsorption work together to affect cell morphology and proliferation, but the strengths of these effects vary in different cell types. Furthermore, it is revealed that stiffness-mediated differentiation of dermal fibroblasts into myofibroblasts is modulated by the substrate ECM. The material system demonstrates remarkable simplicity and flexibility to tune ECM coatings and substrate stiffness and study their effects on cell function.     

The KidSat project

Imagine viewing our world from space; a world astronauts have described as “bright and vivid” with “no borders or boundaries”. Then consider how much can be learned by studying Earth from this unique vantage point. The National Aeronautics and Space Administration (NASA) began a three-year pilot program in 1995 designed by a team of scientists, educators, engineers, and high school and college students to share astronauts' unique view of Earth with middle school students. This pilot program was called KidSat. KidSat's primary objective was to merge real-time professional space flight with middle school education by providing students with equal access and direct contribution to the United States space program for the exploration of the Earth. KidSat's long-term intent was to produce higher student achievement and increased competence in science, math, technology, and geography, and to promote an interactive understanding of Earth as an integrated system. Similar to the regular duties of astronauts, scientists, and engineers, students around the nation planned observations and captured images to study Earth's dynamic, fragile environment, using a remotely operated high-resolution color digital camera onboard the Space Shuttle, custom flight software, the Internet, NASA's infrastructure, and a mission operations infrastructure that linked middle schools to the Shuttle through a student-built mission Control Gateway. Using accompanying curriculum, students determined which areas of Earth they wanted to explore and photograph along the Shuttle's flight path. Orbiting communications satellites and the Internet transmitted commands, telemetry and images to and from the classrooms. Via the Shuttle cargo bay video camera. NASA TV carried video of the mission and the Earth for simultaneous viewing in classrooms. The KidSat pilot program was conceived in November 1993 and ended in December 1997. This paper summarizes the results of this program     

The effects of boron penetration on p+ polysilicon gatedPMOS devices

The penetration of boron into and through the gate oxides of PMOS devices which employ p⁺ doped polysilicon gates is studied. Boron penetration results in large positive shifts in V_FB , increased PMOS subthreshold slope and electron trapping rate, and decreased low-field mobility and interface trap density. Fluorine-related effects caused by BF₂ implantations into the polysilicon gate are shown to result in PMOS threshold voltage instabilities. Inclusion of a phosphorus co-implant or TiSi₂ salicide prior to gate implantation is shown to minimize this effect. The boron penetration phenomenon is modeled by a very shallow, fully-depleted p-type layer in the silicon substrate close to the SiO ₂/Si interface     

A technique for electron microscope autoradiography (and X-ray microanalysis) of diffusible substances using freeze-dried fresh frozen sections

Several attempts have been made over the past few years to localize diffusible radioactive substances in tissues at the electron microscope level. The procedures employed hitherto have involved one or more aspects of the methods used in tissue preparation for conventional electron microscopy and as such are unlikely to be universally applicable for all classes of diffusible substance. The present paper shows that the use of ultrathin frozen sections of fresh unembedded biological material permits the ultrastructural localization by autoradiography and X-ray microanalysis of highly soluble electrolytes.     

△∑转换器中的转换时延

小信号传感器通常生成慢速移动的DC信号。对这类传感器来说,△∑ADC就可以作为完整的高分辨率、低噪声解决方案,而无需大部分模拟输入电路。一些系统采用多个传感器,这些传感器要求输出端带多路复用器的高分辨率、低噪声ADC相匹配。例如,汽车诊断应用就是一种多路夏用传感器系统,其通过焱多小信号传感器监控温度、胎压、气囊就绪情况等（如图1所示）。