Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Optical Absorption Properties of BaSi2 Epitaxial Films Grown on a Transparent Silicon-on-Insulator Substrate Using Molecular Beam Epitaxy

Abstract: We have grown 100-nm-thick BaSi2 films on transparent silicon-on-insulator (SOI) substrates using molecular beam epitaxy, for optical absorption measurements. The SOI substrate has a 0.7-µm-thick (111)-oriented Si layer on top of a fused silica substrate. Reflection high-energy electron diffraction and θ–2θ X-ray diffraction patterns showed that a-axis-oriented BaSi2 layers were grown epitaxially. The absorption spectrum of the film measured in a transmission configuration at room temperature revealed that BaSi2 has a large absorption coefficient of 3 ×104 cm-1 at 1.5 eV and an indirect optical absorption edge of 1.34 eV.

Photoacoustic technique for determining optical absorption coefficients in solids.

Abstract: An investigation was made of a photoacoustic technique for determining the optical absorption coefficient in solids. A train of laser pulses was passed through the solid, and a piezoelectric transducer attached directly to the sample measured the amplitude of the elastic wave generated by the absorbed radiation. Calibration was performed at a wavelength of known absorption. The sensitivity of the technique was found to be limited to about 1 × 10−5 cm−1 in our samples due to radiation scattered onto the transducer, but the technique is capable of measuring absorption coefficients in the 10−6 cm−1 range using laser powers of about 1 W.

Nearest-neighbor oxygen distances in liquid water and ice observed by x-ray Raman based extended x-ray absorption fine structure.

Abstract: We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 A for water and 2.76 A for ice) but a slightly shorter peak position (2.70 A for water and 2.71 A for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water.

Fischer–Tropsch Synthesis: Characterization and Reaction Testing of Cobalt Carbide

Abstract: Hydrogenation of carbon monoxide was investigated for cobalt carbide synthesized from Co3O4 by CO carburization in a fixed-bed reactor. The cobalt carbide synthesized was characterized by BET surface area, X-ray diffraction, scanning electron microscopy, X-ray absorption near edge spectroscopy, and extended X-ray absorption fine structure spectroscopy. The catalysts were tested in the slurry phase using a continuously stirred tank reactor at P = 2.0 MPa, H2/CO = 2:1 in the temperature range of 493–523 K, and with space velocities varying from 1 to 3 Nl h–1 gcat–1. The results strongly suggest that a fraction of cobalt converts to a form with greater metallic character under the conditions employed. This was more pronounced on a Fischer–Tropsch synthesis run conducted at a higher temperature (523 versus 493 K).