Excitations of the $2p$ subshell in the $3d$ transition metals and their oxides have been studied by inelastic scattering of 75-keV electrons. The ${L}_{23}$ "white lines" which arise from dipole transitions to unoccupied $d$ states have been investigated in terms of their threshold energies, widths, and intensity ratios. Shifts in the ${L}_{3}$ threshold energy between the metal and oxide are different from the chemical shifts measured by x-ray photoemission spectroscopy and this suggests the importance of relaxation effects. Single-particle calculations for the ${L}_{3}$ spectra are also discussed. Measured ${L}_{3}$ linewidths are generally larger than those predicted by suitably broadened theory. A variation from the statistical ${L}_{3}$-to-${L}_{2}$ white-line intensity ratio of 2:1 has been observed across the $3d$ transition row, with values ranging between 0.8:1 for Ti to 5:1 for FeO. This behavior appears to be associated with the white lines since Cu with a filled $3d$ band exhibits the statistical results. It is suggested that the anomalous ratios may be explained by a breakdown of $j\ensuremath{-}j$ coupling caused by an exchange mechanism. Finally, the extended x-ray absorption fine-structure-type structure extending several hundred eV above the white lines is analyzed for Cr to provide the radial distribution function.

Study of the L 23 edges in the 3 d transition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory

Angle-resolved x-ray photoelectron spectroscopy

NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

Ion beam crystallography of surfaces and interfaces

Alkali-metal-affected adsorption of molecules on metal surfaces

Orientation of Chemisorbed Molecules from Surface-Absorption Fine-Structure Measurements: CO and NO on Ni(100)

The (111) and (110) surfaces of Pt, clean, oxidized, and covered by CO, have been investigated for surface $4f$ core-level binding-energy shifts. For the (111) face the surface $\mathrm{Pt}4{f}_{\frac{7}{2}}$ core level was shifted by 0.40\ifmmode\pm\else\textpm\fi{}0.05 eV to lower binding energy relative to the bulk peak. On the (110)-(1\ifmmode\times\else\texttimes\fi{}2) reconstructed surface similarly shifted peaks at 0.21\ifmmode\pm\else\textpm\fi{}0.05 and 0.55\ifmmode\pm\else\textpm\fi{}0.05 eV were observed. Chemisorbed carbon monoxide shifts the Pt(111) surface-related core level by 1.3 eV to higher binding energy. Formation of subsurface oxygen did not produce changes in the $\mathrm{Pt}(111)4{f}_{\frac{7}{2}}$ core-level binding energies. The results obtained are explained and their possible implications are discussed.

Surface core-level shifts for Pt single-crystal surfaces

Improvements in the signal-to-noise ratio of surface extended x-ray-absorption fine-structure spectra of chemisorbed low-$Z$ atoms allow for the first time precise determination of complete adsorption geometries. For $c(2\ifmmode\times\else\texttimes\fi{}2)$ S on Ni(100) the first-nearest-neighbor distance is 2.23\ifmmode\pm\else\textpm\fi{}0.02 \AA{} and the adsorption site is the fourfold hollow as independently derived from either the second nearest S-Ni distance, amplitude ratios for three polarization directions, or the absolute S coordination number on the surface.

Structure determination of c(2×2) S on Ni(100) using polarization-dependent surface extended x-ray-absorption fine structure

Structural models for the interaction of oxygen with Al(111) and A1 implied by photoemission and surface exafs

Absorption measurements above the K edges of the low-Z atoms, C, N, O, and F, are discussed, which utilize 250–1000-eV synchrotron radiation. The paper emphasizes experimental procedures of soft x-ray absorption and extended absorption fine structure (EXAFS) measurements as well as applications and future prospects of such studies. In particular, we discuss such applications as surface EXAFS, surface absorption fine structure, and ion yield EXAFS measurements.

R. Jaeger

Papers

Orientation of Chemisorbed Molecules from Surface-Absorption Fine-Structure Measurements: CO and NO on Ni(100)

Surface core-level shifts for Pt single-crystal surfaces

Structure determination of c(2×2) S on Ni(100) using polarization-dependent surface extended x-ray-absorption fine structure

Structural models for the interaction of oxygen with Al(111) and A1 implied by photoemission and surface exafs

Extended absorption fine structure studies above the carbon, nitrogen, oxygen, and fluorine K absorption edges.