New thermoelectric components using microsystem technologies

This paper describes the first thermoelectric devices based on the V-VI-compounds Bi/sub 2/Te/sub 3/ and (Bi,Sb)/sub 2/Te/sub 3/ which can be manufactured by means of regular thin film technology in combination with microsystem technology. Fabrication concept, material deposition for some 10-/spl mu/m-thick layers and the properties of the deposited thermoelectric materials will be reported. First device properties for Peltier-coolers and thermogenerators will be shown as well as investigations on long term and cycling stability. Data on metal/semiconductor contact resistance were extracted form device data. Device characteristics like response time for a Peltier-cooler and power output for a thermogenerator will be compared to commercial devices.     

Low-temperature MBE-grown In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As/InP optical waveguides

The MBE growth of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As ( lambda /sub g/=1.06 mu m) layers in the temperature range of 400-450 degrees C was demonstrated to give high-quality optical waveguides which not only exhibit low propagation losses as low as 0.5 dB/cm at lambda =1.55 mu m but concomitantly high resistivity of >10/sup 4/ Omega cm. The refractive index of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As was estimated to be 3.207+or-0.03 at lambda =1.55 mu m.<>     

Microstructure and transport properties of porous building materials. II: Three-dimensional X-ray tomographic studies

Three-dimensional X-ray microtomography is used to obtain three-dimensional images of the microstructure of two types of brick. The images are processed to remove the noise (random and circular pattern) and then thresholded to match the porosity determined experimentally. The 3-D binary images are then analyzed to estimate their vapor diffusivity and air permeability to compare to experimental data published in part one of this report. Care must be taken in obtaining the tomographic images at a resolution that both enables isolation and quantification of the pores of interest and provides a representative elementary volume for the transport property calculations. In general, the agreement between computed and measured properties is reasonable, suggesting that X-ray microtomography can provide valuable information on the characteristics and properties of the pore networks developed in these porous building materials. A preliminary evaluation indicates that the Katz-Thompson relationship between permeability, diffusivity, and pore size is valid for these materials.

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Résumé La microtomographie à rayons X synchrotron, est utilisée pour obtenir des images tridimensionnelles de la microstructure de deux types de briques. Les images sont tout d’abord traitées pour éliminer le bruit (anneaux aléatoires_ et ensuite seuillées par ajustement avec la porosité déterminée expérimentalement. à partir des images binaires 3D, on estime numériquement la diffusivité à la vapeur et la perméabilité à l’air, les valeurs obtenues sont ensuite comparées avec les données expérimentales publiées dans la partie I de cette communication. Dans le cadre d’une telle procédure, la résolution des images doit à la fois rendre possible la discrimination et la quantification de tous les pores importants vis-à-vis du phénomène étudié et fournir un volume élémentaire représentatif pour le calcul des propriétés de transport. L’accord satisfaisant obtenu entre les valeurs calculées et mesurées montre que la microtomographie X peut fournir des informations pertinentes sur les caractéristiques et les propriétés du réseau poreux des matériaux de construction. Une évaluation préliminaire indique que la relation de Katz-Thompson entre la perméabilité, la diffusivité et la taille des pores est applicable pour ces matériaux.

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Editorial Note Mr. D. P. Bentz is a RILEm Senior, Member. He works at NIST (USA), a titular member. He is also a Member of RILEm Coordinating Committee. He was the 1998 Robert l’Hermite medallist.