Molecular adsorption on oxide surfaces: Electronic structure and orientation of NO on NiO(100)/Ni(100) and on NiO(100) as determined from electron spectroscopies andab initiocluster calculations

Abstract

We have investigated the adsorption of NO on a thin NiO(100) film of several layers thickness grown on top of a Ni{100) surface in comparison with data of an in vacuo cleaved NiO(100) single crystal. The layer exhibits a high defect density. We demonstrate via application of several surface-sensitive electron-spectroscopic techniques [i.e., x-ray photoelectron spectroscopy (XPS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS), near-edge x-ray-absorption fine structure (NEXAFS), and high-resolution electron-energy-loss spectroscopy (HREELS)j that this layer has similar occupied (ARUPS) and unoccupied (NEXAFS) states as a bulk NiO(100) sample. In spite of its limited thickness, the band structure of the film exhibits dispersions perpendicular to the surface compatible with bulk NiO(100). It is shown that the electronic structure of the oxygen sublattice can be described in a band-structure picture while for the Ni sublattice electron localization eftects lead to a breakdown of the band-structure picture. NO on NiO desorbs at 220 K. This indicates weak chemisorption. The NO coverage is close to 0.2 relative to the number of Ni surface atoms as determined by XPS. HREELS reveals that there is only one species on the surface documented by the observation of only one bond-stretching frequency. NEXAFS data on the system and a comparison with previous data on the system NO/Ni(100) indicate that the molecular axis of adsorbed NO is tilted by an angle of approximately 45' relative to the surface normal. The N 1s XP spectra of the weakly chemisorbed species show giant satellites similar to the previously observed cases for weak chemisorption on metal surfaces. This is the first observation of an intense satellite structure for an adsorbate on an insulator surface, which shows that there must be sufficient screening channels even on an insulating surface. A theoretical assignment of the peaks is discussed. We compare the spectroscopic properties of the NO species on the thin-film oxide surface, which is likely to contain a certain number of defects, with NO adsorbed on a basically defect-free bulk oxide surface by thermal-desorption (TDS) and XP spectra. TDS and XP spectra of the bulk system are basically identical as compared with the oxide film, indicating that the majority of species adsorbed on the film is not adsorbed on defects but rather on regular NiO sites. Results of ab initio oxide cluster calculations are used to explain the bonding geometry of NO on regular NiO sites.

LDA+DMFTcomputation of the electronic spectrum of NiO

“…5 Despite the success of the cluster approach it has apparent drawbacks since it neglects the band aspects of O 2p states completely which are known to play an important role in NiO. 8,10 The translational symmetry has been taken into account to some extent within the cluster perturbation theory recently. 11 Another extension is the treatment of a larger cluster (Ni 6 O 19 ) so that nonlocal charge transfer excitations can be identified.…”

X-ray standing-wave investigations of valence electronic structure

“…NiO surfaces were produced by repeated cycles of argon sputtering and annealing in oxygen. 22 For the x-ray standing-wave experiments, the Cu͑111͒ crystal was aligned so that the ͑11Ϫ1͒ diffracting planes were normal to the synchrotron beam, and the NiO͑001͒ crystal was aligned so that the ͑111͒ diffracting planes were normal to the synchrotron beam. For both the Cu and NiO studies, the horizontal axis of the spectrometer was aligned parallel to the polarization vector of the synchrotron radiation.…”

Local Structure of CPO-27-Ni Metallorganic Framework upon Dehydration and Coordination of NO

“…In case of (001) faces of microcrystalline NiO, it has been found that linear NO, formed at low coverages, is accompanied by tilted NO at medium/high coverages, which are characterized by a coverage dependent ν(NO) stretching frequency in the 1805-1799 cm -1 range due to both static and dynamic dipole-dipole interactions (∆ν dyn ) 32 cm -1 and ∆ν st ) -26 cm -1 ). [70][71][72][73][74] The Freund group in Berlin investigated with high resolution EELS the adsorption of NO on thin NiO(001) layers deposited on Ni(001) and on vacuum cleaved NiO(001) single crystal surfaces, 72 finding a ν 0 (NO) of 1800 cm -1 .…”