The reactions of nitric oxide with nickel films as studied by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been employed to study the reactions between nitric oxide and freshly deposited nickel films. When the nickel surface is treated with NO at pressures of less than 1 · 10^?4 torr for 60 s (6000L), the NO is dissociatively adsorbed with no oxidation of the nickel surface. When treated with 0.40 torr of NO that has been exposed to varying degrees of oxidation, the nickel surface is oxidized and species such as NO₃^?, NO₂^?, NO and N₂ may be found on the surface. The species found are determined by the extent of oxidation of NO.     

Oxidation of nickel studied by UV and X-ray photoelectron spectroscopy

The nature of argon-ion bombarded nickel surfaces (polycrystalline, and (111), (110) and (100) single crystals) and their subsequent interaction with oxygen at ordinary temperatures have been studied using X-ray and UV photoelectron spectroscopy, including angular variation measurements and the determination of work function changes, in combination in the same apparatus. Variations between the HeI spectra of the four clean substrates were taken to confirm the presence of substantial order within the depth sampled by UPS. The four surfaces exhibited similar but not identical behaviour during oxidation, resembling that reported by other workers from studies of both annealed single crystals and evaporated polycrystalline films. The initial process was deduced to be essentially dissociative chemisorption: no evidence supporting a previous suggestion of associative adsorption at low coverages was found. Oxygen commenced to penetrate below the surface of all samples before oxygen equivalent to a monolayer had been taken up (~10 L exposure) and further substantial uptake followed resulting in the formation of a stable film (~18 Å) of nickel oxide by ~100 L exposure. This oxide layer was not stoichiometric nickel(II) oxide: it was characterized by the presence of two distinct O 1s signals, the relative intensities of which depended on the crystallographic nature of the surface. It is tentatively suggested that the oxygen signal with the higher BE be associated with Ni^III. Comparison of the X-ray and UV spectra suggests that the oxide film is very non-uniform in thickness, some Ni metal remaining very close to the surface.     

In-situ X-ray photoelectron spectroscopy study of supported gallium oxide

In-situ XPS study of supported gallium oxide catalysts prepared by impregnation of different metal oxides supports (SiO₂, γ-Al₂O₃, TiO₂, and MgO) has been performed. It has been found that the formation of metallic gallium takes place upon high-temperature reduction of the catalysts in flowing hydrogen. Relative concentrations of metallic gallium were most high in the cases of alumina- and titania-supported catalysts. It was suggested that interaction of gallium oxide with a support surface favors the formation of metallic gallium upon high-temperature reduction. A possible mechanism of metallic gallium formation upon the reduction is discussed.     

X-ray photoelectron spectroscopy of tin oxide nanolayers

X-ray photoelectron spectra of 30- and 100-nm nanolayers, recorded in the energy range 0–35 eV, show a strong dependence of both the distribution of the density of Sn 5s, p+ O₂ p valence states and the change in the intensity ratio for the Sn 4d and O 2s subvalence states on the annealing temperature and nanolayer thickness. In the nanolayers fabricated at an annealing temperature of 450°C, an unusually strong band of O 2s states of unbound oxygen is observed, which is retained for nanolayers doped with palladium and disappears for nanolayers doped with gold and silver.     

X-ray study of molecular oxygen adsorbed on graphite

We have performed a detailed X-ray diffraction study of O₂ adsorbed on UCAR-ZYX and Le Carbon Lorraine vermicular exfoliated graphite between 15 and 50 K. At least four phases of physisorbed oxygen are found. The monolayer δ phase consists of a centered parallelogram lattice, with the molecular axes parallel to the graphite surface. The data are consistent with a triple point at 26 K. The melting transition at a coverage of one monolayer appears to be first order. At higher coverages the molecules undergo a lying-down to standing-up transition; the higher coverage ζ phase froms an approximately triangular lattice with the molecular axes perpendicular to the graphite surface. Satellite peaks around the (1, 0) Bragg peak indicate, however, that this cannot be a simple triangular lattice; possible explanations include successively incommensurate layers or a sinusoidal density modulation. For coverages in the two-layer region the ζ phase modulation peaks disappear at 37 K, and at 40 K the adsorbed oxygen appears to undergo a first order melting transition into a fluid phase. With increasing coverage, the 2D X-ray diffraction profiles and phase boundaries do not connect smoothly onto those of the 3D α and β phases. At low temperatures (T < 30 K) the ζ phase always coexists with bulk crystallites; for temperatures near the 2D melting transition the 3D peaks are not observable. These data, taken together with the heat capacity results, suggest a wetting transition with only the bilayer lamellar phase or bulk O₂ being stable at low temperatures.     

Orientation of adsorbed ethylene oxide on Ni(110) by X-ray photoelectron diffraction

The adsorption of ethylene oxide on Ni(110) was studied at 95 K and monolayer coverage by angle-resolved X-ray photoelectron spectroscopy. A slow radiation-induced decomposition at hv = 1486.7 eV to most likely methoxy was noted. The orientation of the adsorbed ethylene oxide was determined by measuring forward scattering enhancements in the O 1s intensity distribution. Peaks in polar (θ) as well as azimuthal (φ) scans occurred at four angular positions in 2π above the surface: (θ = 54°, φ = 36°, 144°, 216°, 324°). These positions were evaluated to yield the tilt angle of the molecule at 48°_relative to normal, and the COC bond angle of adsorbed C₂H₄O of about 57°. The molecule is tilted towards the [001] and [001&#x0304;] directions (two domains), with a mirror plane in the [001] azimuth.     

Analysis of protective oxide films on copper—nickel alloys by photoelectron spectroscopy

Photoelectron spectroscopy was used to determine the elemental composition of thin films formed on 70:30 cupronickel exposed to sodium chloride solutions at different impressed electrochemical potentials. At anodic potentials below the passivation potential, ?0.350 V versus SCE under the experimental conditions, either no film or a film containing copper and nickel in the same ratio as the alloy existed on the alloy. At the passivation potential the spectrum of the passive film indicated primarily nickel oxide and was very similar to the spectrum obtained from a pure nickel specimen passivated in the same environment.     

Characterisation of thin films of bismuth oxide by X-ray photoelectron spectroscopy

The XPS (or ESCA) technique has been used for the characterisation of vacuum-deposited thin films of bismuth oxide. The spectra of Bi metal and Bi₂O₃ powder are used for comparison. The characterisation is carried out by consideration of the positions of the Bi 4f_{$\text{7}\text{2}$} and 4f_{$\text{5}\text{2}$} peaks and by using peak-fitting routines. A lower suboxide of bismuth, and metallic bismuth are observed in bismuth oxide films as evaporated. Oxidation of these films by heating in air results in bismuth(III) oxide. A linear relation is found between the binding energies and oxidation state. The corresponding O 1s spectra for the two types of film are also discussed.     

Electronic structure of nickel porphyrin NiP: Study by X-ray photoelectron and absorption spectroscopy

Physics of the Solid State - Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and...     

X-ray photoelectron spectroscopy study of magnetic films

Ta/NiO_x/Ni₈₁Fe₁₉/Ta films were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field H_ex and the coercivity H_c of NiO_x/Ni₈₁Fe₁₉ as a function of the ratio of Ar to O₂ during the deposition process were studied. The composition and the chemical states in the interface region of NiO_x/NiFe were also investigated using X-ray photoelectron spectroscopy (XPS) and the peak decomposition technique. The results show that the ratio of Ar to O₂ has a great effect on the chemical states of nickel in NiO_x films. The exchange coupling field H_ex and the coercivity H_c of Ta/NiO_x/Ni₈₁Fe₁₉/Ta are thus seriously affected. XPS is shown to be a powerful tool for characterizing magnetic films. Received: 18 July 2001 / Accepted: 21 December 2001 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-010/6232-7283, E-mail: guanghua_yu@263.net     

Evidence from photoelectron spectroscopy for dissociative adsorption of oxygen on nickel oxide

XPS and UPS spectra from oxygen adsorption at high temperature on polycrystalline nickel oxide surfaces pre-heated at 700°C and 1450°C are presented. Adsorption results in complete loss of surface charge on both surfaces. There is an increase in intensity of the 0(1s) 529.7 eV peak, attributed to O^2? ions, and the $\text{Ni}\text{(2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}$ spectra show a shift of intensity to the 854.6 eV peak due to Ni²⁺ ions. The results are compared with previous data from kinetic, conductivity and electrochemical measurements. Agreement with a model of O^2? and nickel vacancy production is demonstrated. UPS spectra indicate considerable reorganisation of electronic charge in the surface of the 1450°C pre-heated oxide, after oxygen adsorption, giving an almost stoichiometric surface similar to that of a cleaved single crystal.     

X-ray diffraction on chlorine adsorbed on graphite

Cl₂ layers adsorbed on Grafoil have been investigated by X-ray diffraction between 78 and 285 K. Mono- and submonolayers crystallize in a parallelogram lauttce, incommensurate with the (001) graphite surfaces, the molecules oriented almost perpendicular to the surface. The structure is closely related to that of the (001) planes of three-dimensional solid chlorine. For coverages above the monolayer completion bulk crystalization sets in.     

Electronic structure of carbyne studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy

The electronic structure of amorphous carbyne has been investigated by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. Carbyne band structure has been calculated semiempirically and the experimental data have been interpreted on the basis of the calculation results. The valence band width was found to be about 20 eV which is the same as that in all other condensed carbon structures. The fine satellite structure near the 1s line of carbon has been studied. It is shown that the energy bands in carbyne are arranged in a mirror-like way relative to the Fermi level. The real carbyne structure is susceptible to conformations which affect primarily the π-subband structure.     

A comparative study on lithium nickel cobalt oxide prepared by different wet chemistry routes

LiNi_0.8Co_0.2O₂ is one of the potential cathode materials for Li-ion battery. Materials with a homogeneous phase, narrow distribution of particle size, and with enhanced performance of Li-ion battery can be achieved by wet chemistry. Coprecipitation, sol–gel, and hydrothermal reactions were used to prepare LiNi_0.8Co_0.2O₂ in order to compare its effects on materials properties. The synthesized products were examined by using a scanning electron microscope, energy dispersive X-ray, X-ray diffractometry, Rietveld refinement, and cyclability measurements. Sol–gel’s sample has superior electrochemical performance to that of coprecipitation. Hydrothermal reaction fails to form the product; however, it was found that the crystal morphology correlates with its local ratio of cobalt-to-nickel content.     

X-ray photoelectron spectra of cobalt compounds

The X-ray photoelectron spectra of a variety of cobalt(II) and cobalt(III) complexes have been investigated. Intense satellite lines were observed for the 2p, 3s and 3p peaks in the case of the high spin cobalt(II) compounds, but not for low spin cobalt(III) complexes. The satellites of the 2p levels are best explained as arising from shake-up processes, whereas those of the 3s and 3p levels are thought to arise largely from multiplet (exchange) splitting of the levels. Multiplet splitting of the 2p level is small and responsible for an increase in the doublet separation of the 2p_1/2, 2p_3/2 spin-orbit levels of the high spin cobalt(II) compounds. The chemical shifts for cobalt differ for the 2p, 3s and 3p levels of the high spin cobalt(II) compounds. Those of the 2p and 3p levels of diamagnetic cobalt(III) and low spin cobalt(II) complexes are equal. The difference in the case of the high spin cobalt(II) compounds is thought to be due to the presence of unpaired 3d electrons.     

X-ray photoelectron spectroscopy study of NiSi formation on shallow junctions

The influence of boron (B)/arsenic (As) on X-ray photoelectron spectroscopy (XPS) study of NiSi formation on shallow junctions is investigated in this paper. The Ni-silicide film was formed after 30 s soak anneal at 450 °C on ultra shallow p+/n or n+/p junctions. The atomic ratio of Ni/Si profile in depth was probed by XPS and the results show that a uniform NiSi layer forms on B-doped p+/n junction while a non-uniform, Ni-rich silicide layer forms on As-doped n+/p junction. It does not agree with the results of other independent phase identification methods such as X-ray diffraction, Rutherford backscattering spectroscopy, and Raman scattering spectroscopy, which all demonstrate the formation of NiSi on both n+/p and p+/n junctions. Comparing the raw binding energy spectra of Ni and Si for each silicide film, the similar spectra for Ni signals are revealed. But the Si signals with an obviously smaller intensity is found to be responsible for the apparent Ni rich silicide formation on As-doped n+/p junction. It indicates that As atoms in the silicide film can affect the sputtering yield of Ni and Si, while no noticeable effect is observed for B atoms. More As atoms than B atoms segregation into the silicide layer is indeed verified by secondary ion mass spectroscopy. And micro-Raman scattering spectroscopy further confirms that the degree of crystallinity for NiSi on n+/p junction is inferior to that on p+/n junction.     

Chemisorption of nitric oxide by nickel

The adsorption of nitric oxide on clean and pre-oxidized nickel has been investigated by X-ray photoelectron spectroscopy. Three distinct states of chemisorption have been recognised at room temperature; one is dissociative while two involve molecularly adsorbed NO. Pre-exposing the nickel surface to oxygen enabled the activity of the surface to be controlled such that adsorption was confined to only one of the molecular states. The two molecular states are suggested to arise from “bent” and “linear” forms of NO.     

X-ray photoelectron spectroscopy study of pyrolytically coated graphite platforms submitted to simulated electrothermal atomic absorption spectrometry conditions

The present work is part of an ongoing project aiming to a better understanding of the mechanisms of atomization on graphite furnace platforms used for electrothermal atomic absorption spectrometry (ETAAS). It reports the study of unused pyrolytic graphite coated platforms of commercial origin, as well as platforms thermally or thermo-chemically treated under simulated ETAAS analysis conditions. X-ray photoelectron spectroscopy (XPS) was employed to study the elements present at the surfaces of the platforms. New, unused platforms showed the presence of molybdenum, of unknown origin, in concentrations up to 1 at.%. Species in two different oxidations states (Mo⁶⁺ and Mo²⁺) were detected by analyzing the Mo 3d spectral region with high resolution XPS. The analysis of the C 1s region demonstrated the presence of several signals, one of these at 283.3 eV related to the presence of Mo carbide. The O 1s region showed also various peaks, including a signal that can be attributed to the presence of MoO₃. Some carbon and oxygen signals were consistent with the presence of CO and C-O- (probably C-OH) groups on the platforms surfaces. Upon thermal treatment up to 2900 °C, the intensity of the Mo signal decreased, but peaks due to Mo oxides (Mo⁶⁺ and Mo⁵⁺) and carbide (Mo²⁺) were still apparent. Thermo-chemical treatment with 3 vol.% HCl solutions and heating up to 2900 °C resulted in further diminution of the Mo signal, with complete disappearance of Mo carbide species. Depth profiling of unused platforms by Ar⁺ ion etching at increasing time periods demonstrated that, upon removal of several layers of carbonaceous material, the Mo signal disappears suggesting that this contamination is present only at the surface of the pyrolytic graphite platform.