We report the design, construction, and performance of a soft x-ray beam line with accessible photon energy 0.8–4.0 keV at the Synchrotron Radiation Center, University of Wisconsin–Madison. The beam line features an ultrahigh-vacuum (UHV) compatible high-precision double-crystal monochromator (DCM) covering Bragg angles 12°–72°, which was designed and built at the Physical Science Laboratory (PSL), University of Wisconsin–Madison. The monochromatic x rays are focused by a bent cylindrical mirror (Ni-coated fused silica, located 7.5 m from the source) into the experimental chamber (located 5.5 m from the mirror) down to a spot less than 1 mm(h)×3 mm(v). During the initial runs, the DCM used a pair of InSb(111) crystals and covered photon energy 1.75–3.7 keV. At the silicon K edge (1840 eV), the beam line delivered about 4×1011 photons/s with stored electron beam at 100 mA at 1 Gev, among the most intense and stable sources currently available at this energy. The energy resolution is about 0.9 eV at the Si K edge.
The high-resolution Al L-edge x-ray-absorption near-edge structure from single-crystal sapphire has been recorded by measuring the total-electron yield and x-ray-fluorescence yield with synchrotron radiation. The edge structures up to 11 eV from the absorption edge are assigned in terms of the transitions of Al 2p electrons to empty levels using molecular-orbital calculations. The post-edge features between 11 and 60 eV above the Al L» absorption edge were found to correlate very well with the interatomic distances from the absorbing atom to its neighboring atoms as predicted by the multiple-scattering model.
The interactions of energetic ions with multi-cation compounds and their consequences in terms of changes in the local electronic structure, which may facilitate intriguing hybridization between O 2p and metal d orbitals and magnetic ordering, are the subject of debate and require a deep understanding of energy transfer processes and magnetic exchange mechanisms. In this study, nanocrystals of ZnFe2O4 were exposed to O7+ ions with an energy of 100 MeV to understand, qualitatively and quantitatively, the metal-ligand field interactions, cation migration and magnetic exchange interactions by employing X-ray absorption fine structure measurements and X-ray magnetic circular dichroism to get deeper mechanistic insights. Nanosized zinc ferrite nanoparticles (NPs) with a size of ∼16 nm synthesized in the cubic spinel phase exhibited deterioration of the crystalline phase when 100 MeV O7+ ions passed through them. However, the size of these NPs remained almost the same. The behaviour of crystal deterioration is associated with the confinement of heat in this interaction. The energy confined inside the nanoparticles promotes cation redistribution as well as the modification of the local electronic structure. Prior to this interaction, almost 42% of Zn2+ ions occupied AO4 tetrahedra; however, this value increased to 63% after the interaction. An inverse effect was observed for metal ion occupancies in BO6 octahedra. The L-edge spectra of Fe and Zn reveal that the spin and valence states of the metal ions were not affected by this interaction. This effect is also supported by K-edge measurements for Fe and Zn. The t2g/eg intensity ratio in the O K-edge spectra decreased after this interaction, which is associated with detachment of Zn2+ ions from the lattice. The extent of hybridization, as estimated from the ratio of the post-edge to the pre-edge region of the O K-edge spectra, decreased after this interaction. The metal-oxygen and metal-metal bond lengths were modified as a result of this interaction, as determined from extended X-ray absorption fine structure measurements. These measurements further support the observation of cation migration from AO4 tetrahedra to AO6 octahedra and vice versa. The Fe L-edge magnetic circular dichroism spectra indicate that Fe3+ ions occupying sites in AO4 tetrahedra and BO6 octahedra exhibited antiferromagnetic-like ordering prior to this interaction. The NPs that interacted with energetic O ions displayed a different kind of magnetic ordering.
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