Karen J. Gaskell

Effect of surrounding point charges on the density functional calculations of NixOx clusters (x = 4–12)

Embedded NixOx clusters (x = 4–12) have been studied by the density‐functional method using compensating point charges of variable magnitude to calculate the ionic charge, bulk modulus, and lattice binding energy. The computations were found to be strongly dependent on the value of the surrounding point charge array and an optimum value could be found by choosing the point charge to reproduce the experimentally observed NiO lattice parameter. This simple, empirical method yields a good match between computed and experimental data, and even small variation from the optimum point charge value produces significant deviation between computed and measured bulk physical parameters. The optimum point charge value depends on the cluster size, but in all cases is significantly less than ±2.0, the formal oxidation state typically employed in cluster modeling of NiO bulk and surface properties. The electronic structure calculated with the optimized point charge magnitude is in general agreement with literature photoemission and XPS data and agrees with the presently accepted picture of the valence band as containing charge‐transfer insulator characteristics. The orbital population near the Fermi level does not depend on the cluster size and is characterized by hybridized Ni 3d and O 2p orbitals with relative oxygen contribution of about 70%.

Valence-band x-ray photoelectron spectroscopic studies of different forms of sodium phosphate

This article reports the valence-band x-ray photoelectron spectroscopy (XPS) of various forms of sodium phosphate. Valence-band spectra are compared to spectra generated from cluster and band-structure calculations. Five different forms of sodium phosphate are studied as follows, Na4P2O7, Na5P3O10, Na4P4O12, Na2H2P2O7, and NaH2PO2. Core-level XPS studies are of little use for differentiating between such similar compounds while valence band photoemission has been found to be particularly effective at identifying subtle differences in surface chemistry. The results indicate that the valence-band region clearly distinguishes between these different phosphates and that these differences can be predicted by spectra generated from both cluster and band-structure calculations.

ZnxNi1-xO Mixed-Metal Oxides by AES

ZnxNi1-xO samples with a compositional range 0 < × ≤ 0.3 were synthesized via thermal dissolution in air and their surface characterized with Auger electron spectroscopy (AES). AES analysis shows the surface composition to be comparable to the bulk composition. These systems are interesting as they place zinc in an octahedral environment which is unusual for zinc normally preferring a tetrahedral environment. This submission contains survey spectra for the homogeneous solid solutions, Zn0.05Ni0.95O, Zn0.1Ni0.9O, Zn0.2Ni0.8O, Zn0.3Ni0.7O and for pure NiO and ZnO. All samples have the rocksalt crystal structure except ZnO which has the Wurtzite crystal structure.

Sodium Polyphosphate (Na4P4O12) by XPS

We report the XPS spectra of sodium polyphosphate. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium polyphosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the (P4O12)4− ion and therefore provide a means for distinguishing this compound from chemically similar compounds such as other phosphates. The valence band, survey, Na 1s, O 1s, C 1s, P 2s, P 2p, and Na 2s levels are reported.

Sodium Hypophosphite Hydrate (NaH2PO2⋅0.8H2O) by XPS

We report the XPS spectra of sodium hypophosphite. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium hypophosphite due to the abscence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the (H2PO2)− ion and therefore provide a means for distinguishing this compound from chemically similar compounds such as other phosphates. The valence band, survey, Na 1s, O 1s, C 1s, P 2p, and Na s levels are reported.

ZnxNi1-xO Mixed-Metal Oxides by XPS and Auger

ZnxNi1-xO samples with a compositional range 0 < × ≤ 0.3 were synthesized via thermal dissolution in air and their surface characterized with x-ray photoelectron spectroscopy (XPS). XPS analysis shows the surface composition to be comparable to the bulk composition. These systems are interesting as they place zinc in an octahedral environment which is unusual for zinc normally preferring a tetrahedral environment. Auger parameter analysis further illustrates this unusual environment yielding a zinc Auger parameter equal to ∼2011 eV, more than 1 eV greater than found for zinc oxide in the wurtzite form, also in the +2 oxidation state. This submission contains the core level and survey spectra for the homogeneous solid solutions, Zn0.05Ni0.95O, Zn0.1Ni0.9O, Zn0.2Ni0.8O, Zn0.3Ni0.7O and for pure NiO and ZnO. All samples have the rocksalt crystal structure except ZnO which has the wurtzite crystal structure.

Sodium Tripolyphosphate (Na5P3O10) by XPS

We report the XPS spectra of sodium tripolyphosphate. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium tripolyphosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the (P3O10)5− ion and therefore provide a means for distinguishing this compound from chemically similar compounds such as other phosphates. The valence band, survey, Na 1s, O 1s, C 1s, P 2s, P 2p, and Na 2s levels are reported.

Sodium Pyrophosphate Decahydrate (Na4P2O7⋅10H2O) by XPS

We report the XPS spectra of sodium pyrophosphate. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium pyrophosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the (P2O7)4− ion and therefore provide a means for distinguishing this compound from chemically similar compounds such as other phosphates. The valence band, survey, Na 1s, O 1s, C 1s, P 2s, P 2p, and Na 2s levels are reported.

Sodium Phosphate Dodecahydrate (Na3PO4⋅12H2O) by XPS

We report the XPS spectra of sodium phosphate. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium phosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the phosphate ion. The valence band, survey, Na 1s, O 1s, C 1s, P 2s, P 2p, and Na 2s levels are reported.

Sodium Dihydrogenpyrophosphate Hexahydrate (Na2H2P2O7⋅6H2O) by XPS

We report the XPS spectra of sodium dihydrogenpyrophosphate. XPS spectra were collected with a VSW HA150 x-ray photoelectron spectrometer using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of sodium dihydrogenpyrophosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The features seen in the valence band are unique to the (H2P2O7)2− ion which shows small but significant differences from the (P2O7)4− ion. The valence band, survey, Na 1s, O 1s, C 1s, P 2s, P 2p, and Na 2s levels are reported.