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Local atomic structure of kesterite type materialsRitter, Konrad 08 November 2021 (has links)
Kesterite sind Verbindungshalbleiter aus ungiftigen und vergleichsweise häufigen Elementen,
die als Absorber in Dünnschichtsolarzellen genutzt werden können. Häufig wird
ihre Zusammensetzung durch Variation der Stöchiometrie oder Legierung verändert, um
ihre Effizienz marktfähig zu machen. Die langreichweitigen, strukturellen Einflüsse dieser
Methoden sind wohl bekannt. Erkenntnisse aus den ähnlichen Chalcopyriten legen jedoch
nahe, dass die lokale atomare Struktur sich nicht im gleichen Maße ändert. In der
vorliegenden Arbeit wurde daher Extended X-ray Absorption Fine Structure spectroscopy
(EXAFS) verwendet, um Veränderungen in der lokalen Struktur von nicht stöchiometrischen
oder legierten Pulverproben und Dünnschichten auf winzigen Skalen zu analysieren. Es
zeigt sich, dass Kesterite viele Eigenschaften ihrer lokalen Struktur auch über signifikante
Zusammensetzungsveränderungen hinaus beibehalten. Trotzdem wird die Wichtigkeit
dieser Untersuchungen deutlich. So kann unter anderem der direkte Einfluss der lokalen
Struktur auf die Bandlücke gezeigt werden. / Kesterite type materials are researched for their ability to form thin film solar cell absorbers
from earth abundant and non-toxic elements. Main routes to increase their efficiencies
to the level of competing materials include compositional variations such as
deviations from stoichiometry and alloying. While the long range structural impacts
of these methods are well known, similarities with chalcopyrites indicate that the local
atomic structure will not change on the same order of magnitude. This thesis hence employs
low temperature Extended X-ray Absorption Fine Structure spectroscopy (EXAFS)
measurements on off-stoichiometric or alloyed powder samples and thin films, to reveal
the small changes in local atomic environments. It is shown that kesterites tend to keep
many aspects of their local atomic structure despite major compositional changes. Yet,
both the impact of these small changes on band gap energy as well as further value of
probing the local atomic structure of kesterite thin films are demonstrated.
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Rossendorf Beamline at ESRF: Biannual Report 2003/2004Schell, N., Scheinost, A. C. January 2005 (has links)
No description available.
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ROBL - a CRG Beamline for Radiochemistry and Materials Research at the ESRFNeumann, Wolfgang, Strauch, Udo, Claußner, Jürgen, Matz, Wolfgang, Reichel, Peter, Funke, Harald, Eichhorn, Frank, Schlenk, Rainer, Krug, Hans, Hüttig, Gudrun, Oehme, Winfried, Dienel, Siegfried, Reich, Tobias, Prokert, Friedrich, Denecke, Melissa A., Schell, Norbert, Bernhard, Gert, Pröhl, Dieter, Brendler, Vinzenz, Betzl, Manfred January 1999 (has links)
The paper describes the Rossendorf Beamline (ROBL) built by the Forschungszentrum Rossendorf at the ESRF. ROBL comprises two different and independently operating experimental stations: a radiochemistry laboratory for X-ray absorption spectroscopy of non-sealed radioactive samples and a general purpose materials research station for X-ray diffraction and reflectometry mainly of thin films and interfaces modified by ion beam techniques. The radiochemistry set-up is worldwide an unique installation at a modern synchrotron radiation source.
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Glyoxalase 2-2: Over-expression and Characterization of a Metallohydrolase from Arabidopsis thalianaWenzel, Nathan F. 25 November 2003 (has links)
No description available.
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Theory and Experiment of Chalcogenide MaterialsPrasai, Binay K. 25 September 2013 (has links)
No description available.
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Constraints on the Short-Range Structure of Amorphous Calcium Phosphate: A Precursor in the Formation of HydroxylapatiteHoeher, Alexandria J. 05 August 2015 (has links)
No description available.
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Surface Complexes Of Lead And Organic Acids At The Hematite / Water InterfaceNoerpel, Matthew Robet January 2015 (has links)
No description available.
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Photoluminescence and Extended X-ray Absorption Fine Structure Studies on CdTe MaterialLiu, Xiangxin 20 June 2006 (has links)
No description available.
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Novel, High Activity Hydroprocessing Catalysts: Iron Group PhosphidesWang, Xianqin 27 March 2002 (has links)
A series of iron, cobalt and nickel transition metal phosphides was synthesized by means of temperature-programmed reduction (TPR) of the corresponding phosphates. The same materials, Fe₂P, CoP and Ni₂P, were also prepared on a silica (SiO₂) support. The phase purity of these catalysts was established by x-ray diffraction (XRD), and the surface properties were determined by N₂ BET specific surface area (Sg) measurements and CO chemisorption. The activities of the silica-supported catalysts were tested in a three-phase trickle bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene using a model liquid feed at realistic conditions (30 atm, 370 °C). The reactivity studies showed that the nickel phosphide (Ni₂P/SiO₂) was the most active of the catalysts. Compared with a commercial Ni-Mo-S/g-Al₂O₃ catalyst at the same conditions, Ni₂P/silica had a substantially higher HDS activity (100 % vs. 76 %) and HDN activity (82 % vs. 38 %).
Because of their good hydrotreating activity, an extensive study of the preparation of silica supported nickel phosphides, Ni₂P/SiO₂, was carried out. The parameters investigated were the phosphorus content and the weight loading of the active phase. The most active composition was found to have a starting synthesis Ni/P ratio close to 1/2, and the best loading of this sample on silica was observed to be 18 wt.%.
Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES) measurements were employed to determine the structures of the supported samples. The main phase before and after reaction was found to be Ni₂P, but some sulfur was found to be retained after reaction.
A comprehensive scrutiny of the HDN reaction mechanism was also made over the Ni₂P/SiO₂ sample (Ni/P = 1/2) by comparing the HDN activity of a series of piperidine derivatives of different structure. It was found that piperidine adsorption involved an a-H activation and nitrogen removal proceeded mainly by means of a b-H activation though an elimination (E2) mechanism. The relative elimination rates depended on the type and number of b-hydrogen atoms. Elimination of b-H atoms attached to tertiary carbon atoms occurred faster than those attached to secondary carbon atoms. Also, the greater the number of the b-H atoms, the higher the elimination rates. The nature of the adsorbed intermediates was probed by Fourier transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TPD) of the probe molecule, ethylamine. This measurement allowed the determination of the likely steps in the hydrodenitrogenation reaction. / Ph. D.
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L'anisotropie magnétique perpendiculaire induite par oxydation et recuit thermique : de la structure au magnétismeMohamed Garad, Houmed 03 April 2012 (has links) (PDF)
Dans le domaine des couches minces (épaisseur~Å) associant un métal magnétique (Fe, Co, Ni) et un élément non magnétique (essentiellement métallique ou isolant), de remarquables propriétés physiques (aimantation, transport) nécessitent des caractérisations structurales fines. En particulier, citons le cas de jonctions tunnel (métal/isolant/métal) à aimantation perpendiculaire qui sont en cours d'étude au laboratoire Spintec (UMR8191 (CEA/CNRS/UJF). Ces nanomatériaux sont déposés par voie physique (pulvérisation cathodique) au sein de ce laboratoire. Ces nanostructures sont également sondées par diffraction aux rayons X au sein de l'Institut Néel (UPR 2940) via une collaboration entre Spintec et une équipe de cet Institut (Surface, interfaces et nanostructures du Département MCMF, Matière Condensée, Matériaux, et Fonctions). Ces mesures de réflectivité X constituent la sonde privilégiée de choix dans la cadre de cette thèse. D'autres voies sont également exploitées: à l'aide des moyens de rayonnement synchrotron tels que la spectroscopie d'absorption de rayons X : EXAFS, XANES et XMCD. La thèse aura pour but d'étudier expérimentalement ces phénomènes en couches continues sur ces empilements à jonction tunnel avec aimantation perpendiculaire. Plus précisément, le travail de thèse permettra de comprendre les mesures magnétiques (effectuées à l'institut Néel notamment par magnétométrie SQUID et HALL à basse température) grâce à une batterie de mesures structurales (diffraction aux rayons X, rasant, figures de pôles, réflectivité, absorption X ...). Notamment, l'influence des paramètres de dépôt (types de couches, épaisseurs, recuits) du matériau sont étudiées via la collaboration entre les différents groupes de recherche précédemment cités. Cette thématique s'inscrit d'une part dans le cadre de travaux menés à Spintec et dédiés à la recherche de nouveaux matériaux à forte valeur ajoutée industrielle (sur le stockage d'information à ultrahaute densité sur media discrets par exemple). Elle s'inscrit d'autre part dans le renforcement de liens entre recherches fondamentales (laboratoire propre du CNRS comme l'institut Néel) et appliquées (CEA), avec un recours aux solides compétences en caractérisations structurales et magnétiques de l'Institut Néel.
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