10 research outputs found
Czochralski growth of silicon bicrystals
No full textUtilization of polycrystalline silicon for solar cell applications poses the problem of the effects of grain boundaries on the electronic properties of this type of material: preferential impurity diffusion at the boundary, electrical properties of the boundary in relation to the existence of dangling bonds and impurities. Silicon bicrystals, where the interface between two adjacent grains can be well defined, have been grown to study the properties of the grain boundaries. Such specimens have been realized by the Czochralski growth technique with p-type and n-type silicon.L'utilisation du silicium polycristallin pour les cellules solaires pose le problème de l'effet des joints de grains sur les propriétés électroniques de ce type de matériau : diffusion des impuretés aux joints de grains, propriétés électriques du joint en relation avec l'existence de liaisons pendantes et d'impuretés. Des bicristaux de silicium où l'interface entre deux grains voisins peut être parfaitement définie ont été préparés pour étudier les propriétés des joints de grains. Les échantillons ont été obtenus par la méthode de Czochralski avec du silicium du type p et du type n
ETUDE PAR MICROSCOPIE ELECTRONIQUE CONVENTIONNELLE EN TRANSMISSION DES DISLOCATIONS INTERGRANULAIRES INTRINSEQUES
No full textPar contraste de déformation ou interférentiel, la microscopie électronique conventionnelle permet l'étude des dislocations intergranulaires parfaites et imparfaites. Le contraste interférentiel donne également des informations sur la structure des joints de coïncidence de faible indice. Différents aspects de la structure des joints sont illustrés à partir de l'exemple du germanium.Using strain or interferential contrast, the conventionnal electron microscopy allows to study perfect and non perfect grain boundary dislocations. Interferential contrast is also used to obtain informations on atomic structure of low index coincidence boundaries. Different aspects of grain boundary structure are illustrated with germanium bicrystals
Atomic structure of grain boundaries in semiconductors
No full textThis paper summarizes the electron microscope observations (high resolution, diffraction and α-fringes) on germanium bicrystals. Observed structures were found isomorphous to those of silicon. They tend to form a 2D-periodic medium with eventually additional linear defects. In pure tilt grain boundaries the tetrahedral coordination is always restored by dangling bond reconstruction. The electrical activity of such grain boundaries can therefore only be due to point defects (intrinsic defects or impurities).Cet article résume l'ensemble des observations en microscopie électronique (haute résolution, diffraction et franges-α) sur les bicristaux de germanium. Les structures observées sont totalement isomorphes à celles qui existent dans le silicium. Elles tendent à former des arrangements bidimensionnels périodiques sur lesquels se superposent éventuellement des défauts linéaires. Sur les joints de flexion il a été montré que l'environnement des atomes reste toujours tetraédrique par reconstruction des liaisons pendantes. L'activité électrique éventuelle de ces joints ne peut donc venir que de défauts ponctuels (intrinsèques ou impuretés)
Recherche des orientations mutuelles optimales entre une phase CFC et une phase CC. Cas du système cuivre-chrome
No full textThe 0-lattice method has been used in order to predict possible mutual orientations between an f. c. c. phase (Cu) and a b. c. c. phase (Cr). The result of these calculations is in good enough agreement with previous experimental observations.La méthode du réseau 0 a été utilisée pour rechercher les orientations mutuelles préférentielles possibles entre les phases du système cuivre-chrome. Les orientations mutuelles favorables déduites des calculs présentent un accord satisfaisant avec les observations expérimentales
STRUCTURE DES JOINTS DE GRAINS DANS LE GERMANIUM
No full textDes joints de flexion symétriques d'axe [011] e t [001] dans le germanium ont été étudiés par microscopie électronique conventionnelle en transmission. Une synthèse de nos principaux résultats dégage quelques caractéristiques de ces joints. Les observations expérimentales sont illustrées par l'étude du joint (1[MATH]0) Σ=5 pour lequel un modèle est proposé.Some [011] and [001] symmetrical tilt grain boundaries in germanium have been studied using conventional T E M. A synthesis of our main results points out some characteristics of these bouniaries. Experimental observations are illustrated with the study of the (1[MATH]0) Σ=5 boundary which is modeled
X-RAY Determination and Analysis of Residual Stresses in Uniform Films and Patterned Lines of Tungsten
No full textAbstractThe determination by X-ray diffraction of the elastic strain tensors and the corresponding stress tensors in uniform films and patterned lines of tungsten was used to investigate the effect of line width. The stresses were found to increase with increasing line width. These experimental results are discussed with respect to the values obtained from a model using a distributed force in the line. The results of the calculations are in agreement with the X-ray measurements. The edge effects appear to be significant for tungsten lines.</jats:p
X-ray Determination and Analysis of Residual Stresses in Uniform Films and Patterned Lines of Tungsten
No full textABSTRACTThe determination by X-ray diffraction of the elastic strain tensors and the corresponding stress tensors in uniform films and patterned lines of tungsten was used to investigate the effect of line width. The stresses were found to increase with increasing line width. These experimental results are discussed with respect to the values obtained from a model using a distributed force in the line. The results of the calculations are in agreement with the X-ray measurements. The edge effects appear to be significant for tungsten lines.</jats:p
X-Ray Diffraction Determination of the Effect of Passivations on Stress in Patterned Lines of Tungsten
No full textABSTRACTThe determination by X-ray diffraction of the elastic strain tensors and the corresponding stress tensors in patterned lines of tungsten has been performed to investigate the effect of various passivation. For unpassivated lines, the stresses are biaxial and decrease with decreasing line width. Passivation over patterned lines results in triaxial tensile stress. The stress along the line is not changed by the passivation. The stress across the line decreases as the line width decreases. The third component of stress, perpendicular to the surface, which appears with the passivation, increases with decreasing line width. High compressive intrinsic stress in the passivation does not result in high tensile stress in the metal line.</jats:p
CHEMICAL HERSCHEL SURVEYS OF STAR FORMING REGIONS (CHESS)
No full textAuthor Institution: California Institute of Technology, Pasadena CA 91125 (email: [email protected])CHESS is an unbiased line survey of low-, intermediate-, and high-mass star forming regions at different stages of their evolution. The eight sources in the CHESS program are observed with the HIFI instrument on board of the Herschel Space Telescope, which provides a high spectral resolution (R) and covers a frequency range from 480 to 1910~GHz. The objective of CHESS is to study the chemical composition and physical conditions in star forming regions and their variation with mass and evolutionary stage. To date about 50\% of the program have been completed. One of the eight objects in the CHESS program is the hot core NGC~6334~I. With an envelope mass of 200~M and temperatures ~K, NGC~6334~I is very line rich. In this object emission lines of more than 40 species have been identified, including first detections of HCl (Lis et al.~2010) and HO (Ossenkopf et al.~2010). Furthermore, several lines of ortho and para water and ammonia have been detected, allowing to determine the ortho/para ratio of these crucial species. In addition many hydrides (HF, CH) and hydride ions (SH, OH, CH) have been found. In the low mass protostar IRAS~16293-2422, another source of our sample, several deuterated species, including the first detection of ND (Bacmann et al.~2010), were found. The data allowed also the first determination of the ortho/para ratio of DH () (Vastel et al.~2010). In this talk I will give a summary of the conducted observation and highlight the most important results
Hedge Fund Contagion and Liquidity
Get PDFUsing hedge fund indices representing eight different styles, we find strong evidence of contagion within the hedge fund sector: controlling for a number of risk factors, the average probability that a hedge fund style index has extreme poor performance (lower 10% tail) increases from 2% to 21% as the number of other hedge fund style indices with extreme poor performance increases from zero to seven. We investigate how changes in funding and asset liquidity intensify this contagion, and find that the likelihood of contagion is high when prime brokerage firms have poor performance (which would be expected to affect hedge fund funding liquidity adversely) and when stock market liquidity (a proxy for asset liquidity) is low. Finally, we examine whether extreme poor performance in the stock, bond, and currency markets is more likely when contagion in the hedge fund sector is high. We find no evidence that contagion in the hedge fund sector is associated with extreme poor performance in the stock and bond markets, but find significant evidence that performance in the currency market is worse when hedge fund contagion is high, consistent with the effects of an unwinding of carry trades.
