Core-level Threshold Research Articles

Valance-Band photoemission intensities in thorium dioxide

Resonant photoemission spectra of the O 2 p-derived valence band of insulating ThO 2 are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5 d corelevel threshold energies (85 ⩽ hv ⩽ 120 eV), resonance is greatest at the bottom of the O 2 p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2 p states and Th 6 d.

Empty states near the Fermi level in Bi2Sr2CaCu2O8.

Unoccupied states are seen at the Fermi level in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ by use of inverse photoemission. They have partial oxygen 2p character, as evidenced by a resonance at the O 2s core-level threshold and by the similarity between the inverse photoemission spectrum and the O 1s absorption edge. These states are likely to be related to the hole states introduced by doping of oxide superconductors. A peak at ${E}_{F}$+2.9 eV can be assigned to the unoccupied Cu 3d states (if they are localized) or to the Bi 6p states (for delocalized Cu 3d states).

5p-5d resonance in Gd

Photoemission measurements of Gd films in the photon energy range 16 to 45 eV indicate that a 5 p - 5 d intershell interaction results in an enhancement of the 5 d emission above the 5p 3 2 and 5p 1 2 core level thresholds. This resonant behavior has been previously observed in Sm, Yb, and Lu. A constant kinetic energy feature that appears only above the 5p 3 2 threshold is tentatively identified as being due to autoionization following the creation of a 5p 3 2 hole with a locally collapsed 5 d- screening orbital as an intermediate step.

Inverse photoemission study of InP, InAs, and InSb.

Unoccupied bulk and surface electronic states of InP, InAs, and InSb are determined via inverse photoemission from their cleaved (110) surfaces. With use of a tunable photon detector, the band dispersion of the lowest p-like bands along the \ensuremath{\Gamma}\ensuremath{\Sigma}KX line is mapped and the critical points ${\ensuremath{\Gamma}}_{15}$ and ${X}_{1}$ of the conduction band are determined (${\ensuremath{\Gamma}}_{15}$=5.3, 4.5, and 4.2 eV and ${X}_{1}$=2.8, 1.9, and 1.8 eV, for InP, InAs, InSb, respectively). Surface resonances are found in the region 1.9--2.7 eV above the valence-band maximum. Resonance effects near the In 4d core-level threshold and the onset of In 4d luminescence are studied.

Ultraviolet-photoemission- and energy-loss-spectroscopy study ofNbNxandZrNx

Reflection electron-energy-loss spectroscopy (ELS) and angle-integrated ultraviolet-photoemission spectroscopy (UPS) have been used to study the electronic properties of the mononitrides of Nb and Zr. Polycrystalline, high-purity transition-metal foils were nitrided by heating in a nitrogen atmosphere. ELS was used to examine collective oscillations (''plasmons'') of the valence electrons and the one-electron core-level thresholds, while UPS at photon energies of 16.8 and 21.2 eV was used to probe the occupied-valence-band density of states. The results provide good qualitative support for existing band-structure and density-of-states calculations for NbN. Strong similarities are found between the present results and those reported previously for VN/sub x/.

Resonant5fvalence-band satellite at the5dthreshold in uranium metal

Photoelectron energy distribution curves for polycrystalline $\ensuremath{\alpha}$-uranium show a giant Fano-type resonance for the intensity of the $5f$ valence-band features at the Fermi energy ${E}_{F}$, when the photon energy is tuned through the $5d$ core absorption edge at around $h\ensuremath{\nu}\ensuremath{\approx}94 \mathrm{to} 103$ eV. Further, a sharp (full width at half maximum = 2.2 eV) $5f$ satellite excitation at an initial energy ${E}_{i}=\ensuremath{-}2.3$ eV below ${E}_{F}$ has been observed, which has a close analogy to the "6 eV satellite" in Ni. This shakeup satellite shows also a strong resonant enhancement (\ensuremath{\ge} 6 times) at the $5d$ core-level threshold, but a distinctly different cross-section dependence. The origin of the resonances of the $5f$ main line and the 2.3-eV satellite is discussed in an atomic framework taking $5f$ and $6d$ screening into account.

Direct recombination and Auger deexcitation channels of La4d→4fresonant excitations in LaB6

La $4{d}^{9}4{f}^{1}$ excited states ($^{1}P_{1}$, $^{3}D_{1}$, and $^{3}P_{1}$) created by resonant photoexcitations $h\ensuremath{\nu}+4{d}^{10}\ensuremath{\rightarrow}4{d}^{9}4{f}^{1}$ decay via direct recombination and Auger deexcitation channels as revealed from a photon energy dependence of photoemission spectra of La${\mathrm{B}}_{6}$. The Auger deexcitation channel is dominant for $^{3}D_{1}$ and $^{3}P_{1}$ excited states below the $4d$ core-level threshold, while for the $^{1}P_{1}$ excited state above the threshold both channels are important to a comparable extent.