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.

Ultralow values of the absorption coefficient of Si obtained from luminescence.

Abstract: Photoluminescence spectra were measured on homogeneously doped silicon at temperatures of 90 and 295 K. By using the generalized Planck law for the emission of luminescence by indirect transitions, values for the absorption coefficient as small as ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ have been obtained for photon energies well below the band gap. At higher photon energies, where absorption coefficients can be obtained from transmission, good agreement with literature data is observed.

Electro-Absorption Effects at the Band Edges of Silicon and Germanium

Abstract: The change in the absorption coefficient $\ensuremath{\Delta}\ensuremath{\alpha}=\ensuremath{\alpha}(\ensuremath{\omega}, \mathcal{E})\ensuremath{-}\ensuremath{\alpha}(\ensuremath{\omega}, 0)$ due to the presence of an electric field $\mathcal{E}$ has been measured for the indirect-absorption edges of silicon and germanium and for the direct-absorption edge in germanium. The results show good qualitative agreement with the theoretical predictions. The quantitative deviations are caused by the presence of excitons and thermal and electric-field broadening, which have not been taken into account in the theory. The energies of the phonons which take part in indirect optical absorption have been determined from the room-temperature data and are in very good agreement with the values found at liquid-helium temperatures by other means.

Structure and Bonding of Gold Metal Clusters, Colloids, and Nanowires Studied by EXAFS, XANES, and WAXS

Abstract: The structure and bonding of a series of gold clusters and gold nanomaterials stabilized by ligands or confined within nanoporous alumina have been investigated using EXAFS, XANES, and WAXS. Two gold clusters stabilized by two different ligands, Au-55(PPh3)(12)Cl-6 and AU(55)(T-8-OSS - SH)(12)Cl-6 were confirmed to be of face-centered cubic structure type with metal-metal distances of 2.785 and 2.794 Angstrom, respectively, shorter than in bulk gold. Colloidal gold of 180 Angstrom diameter stabilized by sulfonated phosphine ligands had structural and electronic properties very similar to those of bulk gold but smaller Debye-Waller factors. The cluster Au-55(PPh3)(12)Cl-6 adsorbed into nanoporous alumina membrane was found to retain its integrity inside the membrane but with slightly longer Au-Au bonds due to some aggregation. The same cluster thermally transformed into colloidal gold within the alumina membrane was found to be almost identical structurally and electronically to the bulk. Gold nanowires electrochemically grown within the nanoporous alumina were found to be composed on average of 120 Angstrom diameter crystallites. These have the same structure as the bulk, but with smaller Debye-Waller factors, indicating either a better crystallinity or that the gold atoms are more tightly held than in the bulk. The difference of area method L-3 - kL(2) was used to quantify the d orbital occupancy. The two ligand-stabilized Au-55 clusters both had a smaller value (2.7) than the bulk material (4.1). The nanomaterials inside the membrane also showed smaller L-3 - kL(2) values. The geometrical and electronic structures of these gold materials how a very clear pattern of buildup as the number of gold atoms increases from Au-55 clusters through Au colloids and nanowires to the bulk metal.