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Your search keyword '"Stephens, Peter"' showing total 4 results
Start Over Author "Stephens, Peter" Publisher american institute of physics
4 results on '"Stephens, Peter"'

1. Construction and performance of a bent crystal x-ray monochromator.

Author

Stephens, Peter W., Eng, Peter J., and Tse, Teddy

Subjects
*MONOCHROMATORS, *X-rays
Abstract

We describe an x-ray monochromator which uses a sagittally bent crystal to focus 5.7 mrad of horizontal divergence. Complete construction details are given, enabling the reader to duplicate the device. The rocking curve width and diffraction efficiency differ insignificantly between the bent (focusing) and flat crystal geometries. The unit has been operated successfully at energies up to 18 keV, providing a seventyfold increase in x-ray flux over unfocused radiation. [ABSTRACT FROM AUTHOR]

Published
1993
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2. A Guinier Camera for SR Powder Diffraction: High Resolution and High Throughput.

Author

Siddons, D. Peter, Hulbert, Steven L., and Stephens, Peter W.

Subjects
*CAMERAS, *OPTICAL diffraction, *SYNCHROTRON radiation sources, *DETECTORS, *X-ray tubes
Abstract

The paper describe a new powder diffraction instrument for synchrotron radiation sources which combines the high throughput of a position-sensitive detector system with the high resolution normally only provided by a crystal analyser. It uses the Guinier geometry which is traditionally used with an x-ray tube source. This geometry adapts well to the synchrotron source, provided proper beam conditioning is applied. The high brightness of the SR source allows a high resolution to be achieved. When combined with a photon-counting silicon microstrip detector array, the system becomes a powerful instrument for radiation-sensitive samples or time-dependent phase transition studies. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2007
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3. Spectroscopic study of (two-dimensional) molecule-based magnets: [MII(TCNE)(NCMe)2][SbF6] (M = Fe, Mn, Ni).

Author

Olson, Christopher, Heth, Christopher L., Lapidus, Saul H., Stephens, Peter W., Halder, Gregory J., and Pokhodnya, Konstantin

Subjects
*MAGNETS, *ACRYLONITRILE, *MOLECULAR structure, *TEMPERATURE effect, *VIBRATION (Mechanics), *ANIONS, *PARAMAGNETISM, *STATISTICAL correlation
Abstract

The M-[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) system is one of the most interesting classes of molecule-based magnets, exhibiting a plethora of compositions and structures (inorganic polymer chains, 2D layers, 3D networks, and amorphous solids) with a wide range of magnetic ordering temperatures (up to 400 K). A systematic study of vibrational (both infrared and, for the first time, Raman) properties of the family of new TCNE-based magnets of MII(TCNE) (NCMe)2[SbF6] [M = Mn, Fe, Ni] composition is discussed in conjunction with their magnetic behavior and newly reso-lved crystal structures. The vibrational properties of the isolated TCNE•- anion in the paramagnetic Bu4N [TCNE•-] salt and recently characterized 2D layered magnet FeII(TCNE)(NCMe)2[FeCl4] are also reported for comparison. Additionally, a linear correlation between νC=C (ag) frequency of the TCNE ligand and its formal charge Z (the spin density on the π* orbital), Z = [1571 - νC=C (ag)]/154.5 [e], is presented. It is shown that monitoring Z by Raman spectroscopy is of great use in providing information that allows understanding the peculiarity of the superexchange interaction in M-[TCNE] magnets and establishing the structure-magnetic properties correlations in this class of magnetic material. [ABSTRACT FROM AUTHOR]

Published
2011
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4. Structure of Haloform Intercalated C60 and its Influence on Superconductive Properties.

Author

Dinnebier, Robert E., Gunnarsson, Olle, Brumm, Holger, Koch, Erik, Stephens, Peter W., Huq, Ashfia, and Jansen, Martin

Subjects
*CRYSTALS, *HALOCARBONS, *X-ray diffraction
Abstract

We have determined the crystal structure of CHCl[SUB3] and CHBr[SUB3] intercalated C[SUB60] using synchrotron x-ray powder-diffraction, and found that the expansion of the lattice mainly takes place in one dimension (triclinic b-axis), leaving planes of C[SUB60] molecules on an approximately hexagonal, slightly expanded lattice. We have performed tight-binding band structure calculations for the surface layer. In spite of the slight expansion of the layers, for the range of dopings where a large T[SUBc] has been observed, the density of states at the Fermi energy is smaller for C[SUB60]-2CHCl[SUB3] and C[SUB60].2CHBr[SUB3] than for C[SUB60]. This suggests that lattice expansion alone cannot explain the increase of T[SUBc]. [ABSTRACT FROM AUTHOR]

Published
2002

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