P. H. Ansari

XAS studies of 1:2:2 transition metal compounds

Abstract X-ray absorption spectroscopy (XAS) investigations of the electronic structure of 4d transition metal (T) based materials are presented. The sensitivity of the white line (WL) feature at the T−L 2,3 edges to the above E F , d-component of the electronic states is first emphasized with a study of the 4d row elements Mo to Ag. This WL based method is then extended to a systematic study of RT 2 X 2 compounds with: R = Gd or Ce; T = Ru, Rh, Pd and Ag; and X = Si, Ge, and Sn. A central interpretation proposed for the 1:2:2 compounds is the identification of a near edge XAS feature with T(4d)−X anti-bonding states split above E F by hybridization. The strength and splitting of this feature are found to decrease in the sequence X = Si→Ge→Sn, consistent with the decreasing bonding interaction. A second interpretation proposed is the decrease of T(4d) states at E F in these compounds relative to the elements.

X‐ray absorption spectroscopy studies of high‐Tc superconductors

X‐ray absorption spectroscopy measurements on rare‐earth (R) and Ba sites in the new superconducting oxides and in binary rare‐earth oxides are discussed. All of the near‐edge spectra appear to manifest a continuum resonance feature whose energy is quantitatively well correlated with the R–O and Ba–O bond lengths. Evidence supporting a second such feature related to the R/Ba interatomic distance is also presented. Finally, simultaneous consideration of both of these features appears consistent with the inverse square‐law expectation for the interatomic distance dependence of the energies of these spectra features.

The near‐edge x‐ray absorption spectroscopy of RT2Si2 and RT2Ge2 compounds

X‐ray absorption near‐edge spectroscopy (XANES) measurements on 1:2:2 compounds of the form RT2X2 with R=Ce and Eu, T=a transition metal, and X=Si or Ge are presented. XANES measurements on each of the three sublattices are used to elucidate elements of the electronic structure of these compounds. In particular, the evidence for the strongly bonded T‐X planes, the coupling of the Ce valence‐state stability to the T‐X planes, and the response of the X‐p orbitals to varying transition‐metal components are discussed.

Fe-fcc layer stabilization in [111]-textured Fe/Pt multilayers

Abstract Multilayered Fe/Pt films were deposited on Si-(111) substrates and manifest a fcc-Pt-(111) structure. The results of extensive X-ray absorption spectroscopy (XAS) measurements are reported on materials with varying Fe-layer thickness. On the basis of both XAS near edge and EXAFS analysis it is possible to clearly identify the Fe-fcc versus Fe-bcc structure in the Fe-layers. The basis of the near edge Fe-phase identification will be supported by theoretical modeling and discussed in terms of literature results. The Fe-bcc/Fe-fcc phase diagram is discussed in terms of the Fe and Pt layer thicknesses. The effective Fe-fcc lattice parameter is estimated to be in the 3.9–4.0 A range and the effective Fe-bcc lattice parameter is estimated to be 0.04 A expanded as compared to bulk α-Fe.

Near-edge x-ray absorption spectroscopy of RT/sub 2/Si/sub 2/ and RT/sub 2/Ge/sub 2/ compounds

X‐ray absorption near‐edge spectroscopy (XANES) measurements on 1:2:2 compounds of the form RT2X2 with R=Ce and Eu, T=a transition metal, and X=Si or Ge are presented. XANES measurements on each of the three sublattices are used to elucidate elements of the electronic structure of these compounds. In particular, the evidence for the strongly bonded T‐X planes, the coupling of the Ce valence‐state stability to the T‐X planes, and the response of the X‐p orbitals to varying transition‐metal components are discussed.