Electronic structure and oxidation of aluminium-modified Ni and Cu surfaces

Changes in the valence bands and core levels of Al-modified Ni and Cu surfaces have been investigated. Interaction of oxygen with such modified surfaces gives rise to $Al_20_3$, leaving the transition metal unaffected

Nature of oxygen adsorbed on metal surfaces as revealed by electron spectroscopy

A review of O adsorption on metals with emphasis on the authors' work on Ag, Cu, and Ni (100), (110), and (111) faces. The available EELS, UPS, and XPS data are discussed. 60 Ref

A core-level photoemission spectroscopic study of the electron-doped superconductor, Nd2-xCexCuO4-δ

A photoemission study of superconducting Nd1.85Ce0.15CuO4-δ shows that Ce in the cuprate is essentially in the 4+ state. While the electron donated by Ce does not appear to affect the Cu 3d band, we still find evidence for the presence of considerable Cu1+ - related configurations due to covalency effects. A role for oxygen holes and Cu1+ species is indicated just as in other cuprate superconductors

Adsorption of oxygen on (100), (110) and (111) surfaces of Ag, Cu and Ni: an electron spectroscopic study

Adsorption of oxygen has been studied on (111), (110) and (100) surfaces of Ag, Cu, and Ni employing XPS and UPS. Besides atomic species with an O(1s) binding energy of \sim 530 eV, molecular adsorption is found on all the three Ag surfaces associated with a characteristic O(1s) binding energy of 532 eV. He II spectra show a feature around 2.5 eV due to the molecular species. Molecular adsorption is also found on all the three surfaces of Cu with a characteristic binding energy of 533 eV. He II spectra show characteristic features due to molecular adsorption on these surfaces at 100 K. The proportion of molecular species is maximum on the (111) surfaces and least on the (110) surfaces of both Ag and Cu. On Ni surfaces, there is no molecular adsorption; a unique O(1s) feature ascribed to $O^{1-}$ species is found at 531 eV. The intensity of this feature does not vary significantly with temperature in contrast to the O(1s) feature due to the molecular species on Ag and Cu surfaces

Adsorption of carbon monoxide on Ni/Ti and Ni/TiO2TiO_2 surfaces prepared in situ in the electron spectrometer: A combined UPS-XPS study

Adsorption of CO on a clean Ti surface is partly associative at 80 K with a 1\pi-4\sigma separation of 4.2 eV, becoming dissociative at 130 K. On Ni- covered Ti surfaces, however, associative adsorption (4\sigma-1\pi, 3.3 eV) occurs at 80 K and partial dissociation, around 200 K. $TiO_2$ is reduced more effectively on annealing, when it is covered with Ni. On the surfaces of Ni deposited on $TiO_2$, there is only dissociative adsorption, unlike on $Ni/Al_20_3$ and $Ni/TiO_2$ (non-annealed) surfaces

A comparative study of the interaction of oxygen with clusters and single-crystal surfaces of nickel

The interaction of oxygen with Ni(lOO), (110) and (111) surfaces as well as with Ni clusters of varying sixes has been investigated by employing core-level spectroscopy. On single-crystal surfaces, the main oxygen species are $O^{1-}$ and $0^{2-}$ with characteristic O(1s) binding energies of 531 and 530 eV, the percentage of the former being \sim 30. At relatively high oxygen exposures, $Ni^{2+}$ and $Ni^{3+}$ are found on these surfaces. On the surfaces of small clusters, $O^{1-}$ is the primary product (\geq 50%) and the proportion of the $0^{2-}$ species increases with the cluster size. The small clusters distinctly show that $Ni^{2+}$ is formed first, followed by $Ni^{3+}$ at higher exposures. A sequence of transformations occurring on Ni surfaces exposed to oxygen is suggested

A comparative study of COCO and N2N_2 adsorbed on clean and promoted transition metal surfaces by a combined use of EELS, XPES and UVPES

CO and $N_2$ adsorbed on transition metal surfaces in the end-on (perpendicular)configuration and possessing bond orders not far below 3, show two-peak u.v. photoelectron spectra with little separation between the $1\pi$ and $5\sigma$ levels. When the molecules are adsorbed on transition metal surfaces modified by Ba or At, the bond order of the adsorbate is close to unity in the case of CO and slightly less than two in the case of $N_2$. These precursor states which undergo facile dissociation to atomic species show three.peak u.v. spectra with well-separated $1\pi$ and $5\sigma$ levels. The ordering of the $1\pi$ and $5\sigma$ levels seems to be different in CO and $N_2$ adsorbed on the promoted. surfaces; furthermore, the $4\sigma$ level is shifted to higher energies in the former. UVPES results suggest that the orientation of the two molecules on the promoted surfaces are likely to be different

Role of the Cu−OCu-O charge-transfer energy in the superconductivity of cuprates: evidence from Cu 2p core-level spectroscopy and theory

Based on Cu 2p core-level spectroscopy and theoretical calculations, it has been demonstrated that the $Cu-O$ charge-transfer excitation energy which determines the Cu 2p satellite intensity also plays a crucial role in the superconductivity of cuprates. The relative intensity of the satellite generally decreases with an increase in the $T_c$ or in the hole concentration in a given series of cuprate superconductors. In the case of $Bi_2Ca_{1-x}R_xSr_2Cu_2O_{8+\delta}$ (R=rare earth), the satellite intensity goes through a minimum around the same composition where the hole concentration as well as the $T_c$ show maxima

Investigation of novel cuprates of the TlCa1-xLnxSr2Cu2O7- δ (Ln=rare earth) series showing electron- or hole-superconductivity depending on the composition

Superconductivity in cuprates of the general formula TlCa1-xLnxSr2Cu2O7+ delta has been investigated as a function of Ln and x. Compositions with 0.25<or=x<or=0.8 are superconducting for all Ln with Tc in the range 60-90 K (except when Ln=Yb where x=1 is also superconducting); the value of the Tc varies with x as well as Ln. When x approximately=0.25, electrons are the majority charge carriers, while holes are the majority carrier when x >0.25. Thus, these cuprates exhibit a composition-dependent electron- or hole-superconductivity. In the normal state, most of the members of the series traverse compositionally determined metal-insulator transitions. High-energy spectroscopies show the presence of Cu in the 1+ and 2+ states. The Raman frequency around 525 cm-1 characteristic of the Tl-O2-Cu linkage is sensitive to both Ln and x, indicating a possible involvement in the mechanism of superconductivity