A perfect crystal X-ray analyser with meV energy resolution
ABSTRACT We present a new method to construct a spherical crystal X-ray energy analyser. The energy analysis is based on high order Bragg reflections from a silicon perfect crystal at angles very close to 90°. In order to preserve the perfect crystal properties in a focusing optics, necessary for meV energy resolution and large angular acceptance, we developed a procedure to mount ≈12 000 small crystals, obtained from the same silicon wafer, on a spherical substrate. The method is based on computer controlled glueing and cycles of etching for each crystal. We obtained analysers with an energy resolution of 1.7±0.5 meV for 21.75 keV X-rays, using the Si(11 11 11) reflection, and with 25 mrad2 angular acceptance. These analysers have been specifically developed for high energy resolution inelastic X-ray scattering.
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ABSTRACT: Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has become a valuable spectroscopic tool, complementing the well established coherent inelastic neutron scattering (INS) technique for phonon dispersion investigations. In the study of crystalline systems IXS is a viable alternative to INS, especially in cases where only small samples are available. Using IXS, we have measured the phonon dispersion of Nd1.86Ce0.14CuO4 + δ along the [ξ, 0, 0] and [ξ, ξ, 0] in-plane directions. Compared to the undoped parent compound, the two highest longitudinal optical (LO) phonon branches are shifted to lower energies because of Coulomb-screening effects brought about by the doped charge carriers. An additional anomalous softening of the highest branch is observed around q = (0.2, 0, 0). This anomalous softening, akin to what has been observed in other compounds, provides evidence for a strong electron-phonon coupling in the electron-doped high-temperature superconductors.International Journal of Modern Physics B 01/2012; 17(04n06). · 0.46 Impact Factor
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ABSTRACT: Optical spectrometers, instruments that work with highly monochromatic light, are commonly rated by the spectral bandwidth, which defines the ability to resolve closely spaced spectral components. Another equally important feature is the spectral contrast, the ability to detect faint objects among these components. Here we demonstrate that a combined effect of angular dispersion (AD) and anomalous transmission (AT) of x rays in Bragg reflection from asymmetrically cut crystals can shape spectral distributions of x rays to profiles with high contrast and small bandwidths. The AD&AT x-ray optics is implemented as a five-reflection, three-crystal arrangement featuring a combination of the above-mentioned attributes so desirable for x-ray monochromators and analyzers: a spectral contrast of ≃500, a bandwidth of ≃0.46 meV, and a remarkably large angular acceptance of ≃107μrad with 9.1 keV x rays. The new optics can become a foundation for the next-generation inelastic x-ray scattering spectrometers for studies of atomic dynamics.Physical Review A 11/2011; · 2.99 Impact Factor
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ABSTRACT: The sound attenuation in the THz region is studied down to T=16 K in glassy glycerol by inelastic x-ray scattering. At striking variance with the decrease found below 100 K in the GHz data, the attenuation in the THz range does not show any T dependence. This result i) indicates the presence of two different attenuation mechanisms, active respectively in the high and low frequency limits; ii) demonstrates the non-dynamic origin of the attenuation of THz sound waves, and confirms a similar conclusion obtained in SiO2 glass by molecular dynamics; and iii) supports the low frequency attenuation mechanism proposed by Fabian and Allen (Phys.Rev.Lett. 82, 1478 (1999)).11/1999;