Search

Your search keyword '"Segre, C. U."' showing total 99 results
Start Over Author "Segre, C. U."
99 results on '"Segre, C. U."'

8. Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution

Author

Mukherjee, Soham, Nag, Angshuman, Kocevski, Vancho, Santra, Pralay K., Balasubramanian, Mahalingam, Chattopadhyay, Soma, Shibata, Tomohiro, Schaefers, Franz, Rusz, Jan, Gerard, Celine, Eriksson, Olle, Segre, C. U., Sarma, Dipankar Das, Mukherjee, Soham, Nag, Angshuman, Kocevski, Vancho, Santra, Pralay K., Balasubramanian, Mahalingam, Chattopadhyay, Soma, Shibata, Tomohiro, Schaefers, Franz, Rusz, Jan, Gerard, Celine, Eriksson, Olle, Segre, C. U., and Sarma, Dipankar Das

Abstract

Extended x-ray absorption fine-structure studies have been performed at the Zn K and Cd K edges for a series of solid solutions of wurtzite Zn1-xCdxS samples with x = 0.0, 0.1, 0.25, 0.5, 0.75, and 1.0, where the lattice parameter as a function of x evolves according to the well-known Vegard's law. In conjunction with extensive, large-scale first-principles electronic structure calculations with full geometry optimizations, these results establish that the percentage variation in the nearest-neighbor bond distances are lower by nearly an order of magnitude compared to what would be expected on the basis of lattice parameter variation, seriously undermining the chemical pressure concept. With experimental results that allow us to probe up to the third coordination shell distances, we provide a direct description of how the local structure, apparently inconsistent with the global structure, evolves very rapidly with interatomic distances to become consistent with it. We show that the basic features of this structural evolution with the composition can be visualized with nearly invariant Zn-S-4 and Cd-S-4 tetrahedral units retaining their structural integrity, while the tilts between these tetrahedral building blocks change with composition to conform to the changing lattice parameters according to the Vegard's law within a relatively short length scale. These results underline the limits of applicability of the chemical pressure concept that has been a favored tool of experimentalists to control physical properties of a large variety of condensed matter systems.

Published
2014
Full Text
View/download PDF

10. Magnetic properties of Er2Fe14B and Nd2Fe14B thin films.

Author

Zasadzinski, J. F., Segre, C. U., and Rippert, E. D.

Subjects
*THIN films, *SPUTTERING (Physics)
Abstract

Presents a study which synthesized thin films of Nd[sub2]Fe[sub14]B and Er[sub2]Fe[sub14]B by direct current sputtering onto single-crystal sapphire substrates. Benefits from thin-film methods; Description of the compounds synthesized; Advantage of thin-film geometry.

Published
1987
Full Text
View/download PDF

11. Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution

Author

Mukherjee, Soham, primary, Nag, Angshuman, additional, Kocevski, Vancho, additional, Santra, Pralay K., additional, Balasubramanian, Mahalingam, additional, Chattopadhyay, Soma, additional, Shibata, Tomohiro, additional, Schaefers, Franz, additional, Rusz, Jan, additional, Gerard, Celine, additional, Eriksson, Olle, additional, Segre, C. U., additional, and Sarma, D. D., additional

Published
2014
Full Text
View/download PDF

12. Dopant activation in Sn-doped Ga2O3 investigated by X-ray absorption spectroscopy.

Author

Siah, S. C., Brandt, R. E., Lim, K., Schelhas, L. T., Jaramillo, R., Heinemann, M. D., Chua, D., Wright, J., Perkins, J. D., Segre, C. U., Gordon, R. G., Toney, M. F., and Buonassisi, T.

Subjects
GALLIUM compounds, TIN, X-ray absorption, OXIDES, DOPING agents (Chemistry), OXIDATION states, CRYSTAL growth, LOW temperatures
Abstract

Doping activity in both beta-phase (β-) and amorphous (a-) Sn-doped gallium oxide (Ga2O3:Sn) is investigated by X-ray absorption spectroscopy(XAS). A single crystal of β-Ga2O3:Sn grown using edge-defined film-fed growth at 1725°C is compared with amorphous Ga2O3:Sn filmsdeposited at low temperature (<300°C). Our XAS analyses indicate that activated Sn dopant atoms in conductive single crystal β-Ga2O3:Sn are present as Sn4+, preferentially substituting for Ga at the octahedral site, as predicted by theoretical calculations. In contrast, inactive Sn atoms in resistive a-Ga2O3:Sn are present in either +2 or +4 charge states depending on growth conditions. These observations suggest the importance of growing Ga2O3:Sn at high temperature to obtain a crystalline phase and controlling the oxidation state of Sn during growth to achieve dopant activation. [ABSTRACT FROM AUTHOR]

Published
2015
Full Text
View/download PDF

16. The New MRCAT (Sector 10) Bending Magnet Beamline at the Advanced Photon Source

Author

Kropf, A. J., primary, Katsoudas, J., additional, Chattopadhyay, S., additional, Shibata, T., additional, Lang, E. A., additional, Zyryanov, V. N., additional, Ravel, B., additional, McIvor, K., additional, Kemner, K. M., additional, Scheckel, K. G., additional, Bare, S. R., additional, Terry, J., additional, Kelly, S. D., additional, Bunker, B. A., additional, Segre, C. U., additional, Garrett, R., additional, Gentle, I., additional, Nugent, K., additional, and Wilkins, S., additional

Published
2010
Full Text
View/download PDF

25. The MRCAT insertion device beamline at the Advanced Photon Source.

Author

Segre, C. U., Leyarovska, N. E., Chapman, L. D., Lavender, W. M., Plag, P. W., King, A. S., Kropf, A. J., Bunker, B. A., Kemner, K. M., Dutta, P., Duran, R. S., and Kaduk, J.

Subjects
*PHOTONS, *MATERIALS science, *X-rays, *SEMICONDUCTORS
Abstract

The Materials Research Collaborative Access Team (MRCAT) beamline 10-ID at the Advanced Photon Source has been in Commissioning since January 1998. This Beamline has been designed as a flexible spectroscopy, scattering, and diffraction facility for the study of materials in situ. Over 70 users have performed experiments at the beamline during this period. Details about the beamline layout, components, performance and configuration for typical experiments will be presented © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

26. A bent Laue analyzer detection system for dilute fluorescence XAFS.

Author

Karanfil, C., Zhong, Z., Chapman, L. D., Fischetti, R., Bunker, G. B., Segre, C. U., and Bunker, B. A.

Subjects
MAGNETIC analyzers (Nuclear physics), X-ray spectroscopy
Abstract

An analyzer for detection of fluorescence radiation has been developed for XAFS of dilute samples in the 15–25keV range. The analyzer is a thin bent Laue crystal of logarithmic spiral shape held in a machined frame. A large solid angle of k fluorescence lines can be collected with moderate reflectivity using the asymmetric [111] reflection of a silicon crystal 200 microns thick. The crystal (35mm by 120mm active area) covers a solid angle of 0.1 sr of the sample fluorescence. A set of Soller slits to match the virtual x-ray source and reject scatter were designed and fabricated. Experiments were performed at the APS BioCAT and MRCAT ID beamlines using silver fluorescence x-rays. Measurements of the performance of this device and plans for a detection system are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

27. A robust cryogenic crystal design in use at the APS.

Author

Ivanov, Ivan, Rosenbaum, Gerd, Chrzas, John, Fischetti, Robert, Segre, C. U., and Chapman, L. D.

Subjects
SILICON crystals, LOW temperature engineering, SYNCHROTRON radiation sources
Abstract

A simple and robust design for the liquid nitrogen-cooled first monochromator crystal suitable for large Bragg-angles has been implemented at three undulator beamlines at the Advanced Photon Source (IMCA CAT, BioCAT, and MR CAT). The design features a simple and reliable seal and a strain free mount. The system has been pressure tested intentionally and accidentally to failure and the crystal reseals. Measurements have been made under closed gap conditions with little indication of distortion. The crystal design, implementation and measurements are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

28. A ‘beam cleaner’ for harmonic selection/rejection.

Author

Karanfil, C., Chapman, L. D., Bunker, G. B., Segre, C. U., and Leyarovska, N. E.

Subjects
ELECTRICAL harmonics, MONOCHROMATORS, OPTICAL diffraction, KINEMATICS
Abstract

A ‘beam cleaner’ for selection of a harmonic from the beamline monochromator and rejection of other harmonics has been developed using a bent Laue crystal post-monochromator. This is a set of cylindrically bent Si (111) crystals that are aligned to diffract the 2nd harmonic (3× fundamental) from the beamline Si (111) monochromator. This device will reject the fundamental and other harmonics up to the Si (999) reflection from the monochromator. It has particular advantages over a flat crystal device since the reflectivity width is approximately 0.2 milliradian. This makes it insensitive to vibration and alignment errors. Over a narrow energy range it does not require adjustment. The diffraction efficiency of each crystal at 25 keV is ∼80% with an overall efficiency of the crystal pair ∼60%. The device is intended to be used for EXAFS at higher x-ray energies using the beamline monochromator harmonic. An additional benefit is that the crystal set can be passively adjusted to nearly eliminate (to the micron level) the vertical beam motion of a channel-cut mode beamline monochromator. Measurements and plans are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

33. EXAFS Studies of Nanocrystals of Zn1-xMnxO: A Dilute Magnetic Semiconductor Oxide System.

Author

Chattopadhyay, S., Kelly, S. D., Shibata, T., Viswanatha, R., Balasubramanian, M., Stoupin, S., Segre, C. U., and Sarma, D. D.

Subjects
NANOCRYSTALS, EXTENDED X-ray absorption fine structure, MAGNETIC semiconductors, MAGNESIUM, OXIDES
Abstract

Zn edge and Mn edge EXAFS studies have been performed on bulk and nanocrystals (4.7 nm) of the dilute magnetic semiconductor Zn1-xMnxO, with x varying from 0.05 to 0.5. Preliminary analysis and linear combination fitting shows that Mn replaces Zn in the bulk sample, whereas in the nanocrystal samples, with different amounts of Mn, only a very small percentage of the Mn atoms replace Zn. The majority of the Mn atoms remain on the surface of the nanocrystallites in the form of Mn oxides. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2007
Full Text
View/download PDF

35. Superconductivity in (Y1−xSrx) (Ba1.5Sr0.5)Cu3O7−dcompounds

Author

Matacotta, F C, Moyo, T, Arhuis, J Ramos, Segre, C U, Siddiqi, S A, and Migliori, A

Abstract

Careful characterization of (Y0.95Sr0.05)(Ba1.5Sr0.5)Cu3O7−δand Y(Ba1.5Sr0.5)Cu3O7−δceramic samples has confirmed the simultaneous substitution of Sr for both Y and Ba in the YBa2Cu3O7structure. The substitution at the Y site has a distinct effect on the superconducting properties of the material. The inter-grain transport properties of both samples in an external d.c. field are enhanced with respect to undoped YBa2Cu3O7ceramics.

Published
1991
Full Text
View/download PDF

36. Structure of the single-phase high-temperature superconductor YBa2Cu3O7-δ.

Author

Beno, M. A., Soderholm, L., Capone, D. W., Hinks, D. G., Jorgensen, J. D., Grace, J. D., Schuller, Ivan K., Segre, C. U., and Zhang, K.

Subjects
COPPER oxide superconductors, HIGH temperature superconductors, STOICHIOMETRY, CRYSTAL lattices
Abstract

We have determined the crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y-Ba-Cu-O system using high-resolution neutron powder diffraction. This compound has an orthorhombic structure with space group Pmmm and lattice constants a=3.8231 Å, b=3.8864 Å, and c=11.6807 Å. The structure consists of ‘‘dimpled’’ CuO2 layers in the a-b planes loosely bonded by one-dimensional fencelike square-planar CuO3 chains in the b-c planes. [ABSTRACT FROM AUTHOR]

Published
1987
Full Text
View/download PDF

37. Phase diagram and superconductivity in the Y-Ba-Cu-O system.

Author

Hinks, D. G., Soderholm, L., Capone, D. W., Jorgensen, J. D., Schuller, Ivan K., Segre, C. U., Zhang, K., and Grace, J. D.

Subjects
PHASE diagrams, HIGH temperature superconductivity, CRITICAL currents
Abstract

We have determined the phase diagram of the Y-Ba-Cu-O system through structural, superconducting critical temperature and critical current density characterization. Our results show that a single-phase compound with a stoichiometry YBa2Cu3Oy is responsible for the high-temperature superconductivity (92.5 K) in this system. [ABSTRACT FROM AUTHOR]

Published
1987
Full Text
View/download PDF

45. Raman scattering from high-Tcsuperconductors

Author

Bhadra, R., primary, Brun, T. O., additional, Beno, M. A., additional, Dabrowski, B., additional, Hinks, D. G., additional, Liu, J. Z., additional, Jorgensen, J. D., additional, Nowicki, L. J., additional, Paulikas, A. P., additional, Schuller, Ivan K., additional, Segre, C. U., additional, Soderholm, L., additional, Veal, B., additional, Wang, H. H., additional, Williams, J. M., additional, Zhang, K., additional, and Grimsditch, M., additional

Published
1988
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results