Showing papers on "Chemical state published in 2000"

Profiling nitrogen in ultrathin silicon oxynitrides with angle-resolved x-ray photoelectron spectroscopy

Abstract: Angle-resolved x-ray photoelectron spectroscopy (AR–XPS) is utilized in this work to accurately and nondestructively determine the nitrogen concentration and profile in ultrathin SiOxNy films. With furnace growth at 800–850 °C using nitric oxide (NO) and oxygen, 1013–1015 cm−2 of nitrogen is incorporated in the ultrathin (⩽4 nm) oxide films. Additional nitrogen can be incorporated by low energy ion (15N2) implantation. The nitrogen profile and nitrogen chemical bonding states are analyzed as a function of the depth to understand the distribution of nitrogen incorporation during the SiOxNy thermal growth process. AR–XPS is shown to yield accurate nitrogen profiles that agree well with both medium energy ion scattering and secondary ion mass spectrometry analysis. Preferential nitrogen accumulation near the SiOxNy/Si interface is observed with a NO annealing, and nitrogen is shown to bond to both silicon and oxygen in multiple distinct chemical states, whose thermal stability bears implications on the relia...

Influence on the gas sensor performances of the metal chemical states introduced by impregnation of calcinated SnO2 sol–gel nanocrystals

Abstract: The effects of the introduction of Pt and Pd by impregnation in sol–gel fabricated SnO 2 nanoparticles after calcination are reported in this paper. The differences in base resistance and sensitivity of sensors prepared using these powders are presented and explained — taking into account the chemical states of the metal additives and the generated surface states in the band gap of the SnO 2 .

X-Ray and Vibrational Spectroscopy of Sulfate in Earth Materials

Abstract: Sulfate is one of the most abundant inorganic ligands in the lithosphere and hydrosphere. It plays a major role in mediating mineral dissolution and precipitation, crystal growth, mineral–water and air–water interfacial reactions, aerosol chemistry and global climate, and biogeochemical cycling of several elements including inorganic and organic toxic contaminants. For several years, macroscopic methods and thermodynamic models have been used in understanding and predicting the geochemistry of sulfate in a variety of systems. As shown by several recent studies, molecular chemistry of chemical species cannot be identified by the macroscopic methods alone (Sposito 1990, Brown et al. 1999). Although researchers have been using different spectroscopic methods (especially infrared spectroscopy, IR) for examining sulfate molecular chemistry, sulfate in geologic materials has not been probed as extensively as some of the other oxoanions, such as chromate, selenate and arsenate. Details of different spectroscopic methods and their applications in geochemical studies are discussed by Hawthorne (1988). The molecular properties of sulfate, such as coordination environment (types of connecting atoms, their number and bond distances), electronic state, and symmetry, dictate how sulfate reacts in a geochemical system. Several electronic states exist in a molecule, with each electronic state containing several vibrational states, and each vibrational state containing several rotational states (Fig. 1⇓). The energies and probabilities of transitions between different electronic, vibrational, or rotational states can be measured and used in the identification of molecules and their chemical states. However, transitions among all of these states in a molecule are not feasible and the molecule symmetry determines whether a particular transition is allowed or forbidden (Cotton 1971). A variety of electron, X-ray, and optical spectroscopic methods can be used in studying the core (innermost) and valence (outermost) electronic transitions, and infrared and Raman spectroscopic methods can be used to obtain information …

Stability and excitation of potassium promoter in iron catalysts - the role of KFeO2 and KAlO2 phases

Abstract: Well‐characterized catalyst model compounds of KAlO2 and KFeO2 are investigated by thermal desorption of potassium from the material. The desorbing fluxes of ions, atoms and highly excited states (field ionizable Rydberg states) were studied with surface and field ionization detectors in a vacuum apparatus. From the Arrhenius plots the activation energies for desorption of K and K+ were determined. The chemical state of potassium at the surfaces is concluded to be: ionic on KAlO2 (with the K desorption barrier of 1.76 eV) and covalent on KFeO2 (barrier of 2.73 eV). These results agree with the data obtained earlier for industrial catalysts for ammonia and styrene production. They are interpreted in terms of the Schottky cycle, which is completed for KAlO2 and fails for KFeO2. This failure indicates a non‐equilibrium desorption process. K Rydberg states are only found to desorb from KFeO2, in agreement with the suggestion that such states in some way are responsible for the catalytic activity.

Chemical state of (Ta, Si)N reactively sputtered coating on a high-speed steel substrate

Abstract: The chemical state of (Ta, Si)N coating reactively sputtered on a high-speed steel substrate was studied by XRD, AES and XPS Reactive sputtering was conducted by using Ta 5 Si 3 target with the flux of N 2 as the major variable, ranging from 4 to 20 sccm In the as-deposited condition, the major phase was found to be TaN containing Si in solution and with the N content increasing with the flux of N 2 during deposition The chemical state of Ta was complex in that TaN, Ta 2 O 5 and other ionic states of Ta co-existed in the oxide Si, in addition to the existence in TaN, also formed an Si 3 N 4 compound When the reactively sputtered samples were annealing heat treated at 1000°C, an outward diffusion of C and Fe from the substrate changed the chemical composition of the coating The concentration of C and Fe increased considerably across the whole thickness of the coating while that of Si showed a small increase at the interface of the coating and the substrate In addition, formation of TaC was confirmed in the coating The microhardness of the coating increased with the nitrogen flux and the annealing heat treatment that also increased the critical load in the adhesion test Formation of the multiphase compounds in the coating and enrichment of the interface with Fe was suggested to be responsible for the improvement of the mechanical properties caused by the post-coating annealing heat treatment

XPS and TEM study of new carbon material: N-containing catalytic filamentous carbon

Abstract: N-containing fibrous carbon material prepared by decomposition of CH4/H2/pyridine mixtures over Ni–Cu catalysts has been studied by X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The essential effect of the decomposition temperature (in the range of 820–1020 K) and reaction mixture composition on the nitrogen content, its chemical state and the texture of produced carbon filaments was found.

Surface characterization of polydimethylsiloxane treated pharmaceutical glass containers by X-ray-excited photo- and Auger electron spectroscopy.

Abstract: The siliconization of pharmaceutical glass containers is an industrially frequently applied procedure. It is done by spreading an aqueous silicone oil emulsion film on the inner surface and successive heat curing treatment at temperatures above 300 degrees C for 10-30 min. It was often proposed that a covalent bonding of PDMS to the glass or branching of the linear PDMS occurs during heat treatment. The present study was performed for a detailed investigation of the glass and silicone (polydimethylsiloxane = PDMS) chemical state before and after heat-curing treatment and analysis of the bond nature. Combined X-ray excited photoelectron (XPS) and Auger electron spectroscopy as well as angle resolved XPS-measurements were used for analysis of the glass samples. The silicon surface atoms of the borosilicate container glass were transformed to a quartz-like compound whereas the former linear PDMS had a branched, two-dimensional structure after the heat curing treatment. It was concluded that the branching indicates the formation of new siloxane bonds to the glass surface via hydroxyl groups. Further evidence for the presence of bonded PDMS at the glass surface can be found in the valence band spectra of the siliconized and untreated samples. However, this bond could not be detected directly due to its very similar nature to the siloxane bonds of the glass matrix and the organosilicon backbone of PDMS. Due to the high variation of data from the siliconized samples it was concluded, that the silicone film is not homogeneous. Previously raised theories of reactions during heat-curing glass siliconization are supported by the XPS data of this investigation. Yet, the postulation of fixing or baking the silicone on the glass surface is only partially true since the bonded layer is very thin and most of the silicone originally on the surface after heat curing can be removed by suitable solvents. This fraction can therefore still interact with drug products being in contact to the siliconized container wall.

Microstructure and chemical state of Ti1-xYxN film deposited by reactive magnetron sputtering

Abstract: A feasibility of using Ti1−xYxN as a hard coating material was investigated. Coatings were made on a Si(100) surface as well as on a steel surface using a dual-target rf-dc reactive magnetron sputtering method with the range of Y varying from x=0 to x=0.16. By x-ray diffraction analysis, it was found that all the coated films were of a single phase with a NaCl structure, with their lattice parameters increasing with Y content. A transmission electron microscopy analysis of the coated film revealed fine columnar grains in the samples containing high NY. This was attributed to Y atoms of low surface mobility and a strong bonding tendency with oxygen. The Y atoms promote the rate of heterogeneous nucleation by easily forming fine oxide particles at the substrate surface. From x-ray photoelectron spectroscopy analysis, it was learned that the binding energies of Y 3d5/2 and N 1s in YN bonding were 157.8 and 397.5 eV, respectively. The optimum combination of microhardness and adhesion strength was obtained in ...

Two successive effects in the interaction of nanocrystalline SnO2 thin films with reducing gases

Abstract: Interaction of pure and doped (Pd, Pt, Cu, Ni) nanocrystalline SnO2 thin films with different reducing gases (H2, CO, C3H8/C4H10) was studied in a temperature range of 30–400°C in situ by the electrical response processing. Two successive effects of conductance growth were found. It is supposed that the more pronounced second effect may be associated with tin dioxide and doping metal oxides transformations resulting from the consumption of lattice oxygen in redox reactions on the SnO2 grain surface. The variation of the chemical state of elements during annealing in different gas atmospheres was determined by the X-ray Photoelectron Spectroscopy (XPS) method. A special procedure of thin film annealing was proposed to reduce the induction period necessary for the second peak to appear.

Crystal-field splitting in coadsorbate systems: c (2x2) CO/K/Ni (100)

Abstract: It is demonstrated how the crystal field splitting (CFS) fine structure can be used to characterize a coadsor-bate system. We have applied K 2p x-ray absorption spectroscopy (XAS) to the c(2x2) CO/K/Ni(100) system. The CFS fine structure is shown to be sensitive to the the local atomic environment, the level of interaction, and the chemical state of the alkali atoms. From angle dependent XAS measurements, combined with x-ray photoelectron spectroscopy, a significant K-CO electrostatic adsorbate-adsorbate interaction is found, whereas the K-Ni interaction is substantially weaker. The present results provide evidence for a coad-sorbed overlayer best described in terms of the properties associated with an ionic (two-dimensional) crystal.

In Situ Observation of the Potential-Dependent Chemical State and Structure of a Cu Monolayer Deposited on the Surface of Carbon-Supported Platinum Clusters

Abstract: A complete electrochemical oxidation−reduction cycle for a Cu monolayer on carbon-supported Pt clusters in alkaline solution has been monitored in situ by X-ray absorption spectroscopy. No desorption of Cu was observed upon oxidation. Near-range order and oxidation state of the Cu layer as a function of potential was obtained by in situ X-ray absorption spectroscopy. In contrast to bulk copper, the adsorbed copper monolayer transforms directly from the reduced state to Cu2+ and from the oxidized form to Cu0. Adsorption of OH- ions on the Cu layer was observed for potentials below those for the Cu0 → Cu2+ and Cu2+ → Cu0 transitions.

Iron oxide thin films prepared by ion beam induced chemical vapor deposition: Structural characterization by infrared spectroscopy

Abstract: Iron oxide thin films as hematite (α-Fe2O3) have been prepared by ion beam induced chemical vapor deposition. Very compact and dense films are obtained by this procedure. The thin films have been grown by bombardment of the substrate surfaces with O2+ ions or mixtures of O2+ and Ar+ ions, while a volatile precursor of iron [i.e., Fe(CO)5] is dosed onto the substrate surface. In the latter case, Ar atoms are incorporated within the iron oxide lattice. Atomic force microscopy, Rutherford backscattering spectroscopy, and x-ray photoelectron spectroscopy were utilized to characterize the films’ surface morphology, stoichiometry and chemical state. The film structure has been analyzed by grazing angle x-ray diffraction (XRD) and infrared spectroscopies. In particular, infrared spectroscopy has permitted a thorough structural characterization of the films, even in the cases where XRD does not provide information about the structure. Thus, when O2+ ions are used for the synthesis, iron oxide thin films grow with...

Biomimetic deposition of calcium phosphates on oxides soaked in a simulated body fluid

Abstract: 31P magic-angle-spinning (MAS) NMR spectra were measured for several oxides, such as Al2O3, SiO2, TiO2 and Ta2O5 which were treated with TaCl5-free H2O2 solutions and TaCl5-containing H2O2 solutions and soaked in a simulated body fluid (Kokubo solution; pH=7.4) for 7 days. The chemical states of phosphate anions deposited on these oxides were determined. A 31P MAS-NMR peak at a chemical shift ca. 3 ppm was observed in the spectra of Ta2O5 and for the other oxides when they were treated with the TaCl5-containing H2O2 solution. Without the treatment with the TaCl5-containing H2O2 solution no 31P MAS-NMR peaks were observed in the spectra of the oxides. The 31P chemical shift, ca. 3 ppm, indicated that orthophosphate anions, PO43− as found in hydroxyapatite and a cortical bone (rabbit) were adsorbed on the oxides. The surface of Ta2O5 particles and the oxides treated with the TaCl5-containing H2O2 solution induced the deposition of apatite. We concluded that the surface Ta(V) species supported on the oxides induced a bone-like apatite nucleus, even though the base oxides did not deposit apatite.

Surface segregation of transition metals in sol-gel silica films

Abstract: Silica sol-gel films (SGFs) doped with various transition metals derived by spin-coating on glass substrates and silicon wafers have been studied. Precursor solutions were prepared by mixing tetraethylorthosilicate, ethanol, water and nitrates of the transition metals (Cr, Mn, Fe, Co, Ni and Cu) using HCl as a catalyst. Remarkable segregation of metals at the surface was observed for films doped with Cu and Co. For Mn- and Ni-doped films this effect was much less, and it vanished for the films doped with Cr or Fe. The influence of boron and phosphorus upon the chemical state and the distribution of metal atoms was also analysed. The structure, optical properties and composition of the SGFs were studied and some pathways to control the dopant segregation effect were realized.

Oxidation and chemical state analysis of polycrystalline magnetron sputtered (Ti, Al)N films at ambient and liquid N2 temperatures

Abstract: In order to improve the functional properties of hard coatings, recent investigations have been directed towards Ti–N based multicomponent materials. The nitride (Ti, Al)N, in particular, with a Ti:Al ratio of 1:1 seems to be a promising alternative to the widely used TiN, exhibits better oxidation resistance and hence improved performance over that of TiN. (Ti, Al)N coatings were dc sputter deposited onto 316SS substrates under ambient and liquid nitrogen temperatures. As deposited films were oxidized in a vertical fused-silica tube furnace in pure O2 flowing atmosphere at temperatures ranging from 700 to 900 °C. Scanning electron microscope and atomic force microscope images reveal information about the particle size and film thickness. X-ray photoelectron spectroscopy was employed to study the chemistry of the top few atomic layers in addition to compositional analysis and information on the details of chemical bonding. The difference in film stoichiometry are compared at two different deposition conditions thus reflecting their behavior under oxidizing conditions.

Thin Ta2O5 Films on Si by XPS

Abstract: X-ray photoelectron spectra (XPS) for thermally grown (oxidation temperature 673 K) thin (13 nm) tantalum pentoxide films on Si are presented. The peak decomposition technique was employed to identify the composition and the chemical state throughout the film. It is established that stoichiometric Ta2O5 detected at the surface of the layer is reduced to tantalum suboxides in its depth, which amount increases in the depth of Ta2O5 film. The films have a two-layer structure (i.e., silicon dioxide at the interface with Si and tantalum oxide above it) suggesting oxidation of silicon substrate in addition to oxidation of the tantalum film on Si. The interface between Si and this ultra thin SiO2 is not abrupt and the coexistence of Si–O and Ta–O bonding states in close proximity to the interface is found. The thicknesses of both the tantalum oxide and the SiO2, as well as the width of the Si–SiO2 interface transition region are evaluated.

Surface chemical effects of low‐energy N2+ ion bombardment on single crystalline α‐Al2O3

Abstract: Composition changes and chemical structure alterations initiated by ion beams on metal oxide surfaces have been widely studied Significant differences in the effect of low-keV inert (Ar + ) and reactive (N 2 + ) ion impact on a series of metal oxides have been published recently by the present authors In this work the effect of 05-5 keV N 2 + bombardment on single crystalline α-Al 2 O 3 was studied by quantitative XPS Clarifying the existing ambiguity, experimental evidence is presented that supports the preferential oxygen loss and build-up of nitrogen The oxygen loss increased with increasing N 2 + ion energy until approaching an atomic ratio saturation value of O/Al ∼1 on 35 keV bombardment with the concomitant build-up of N at N/Al ∼05 In contrast to other oxides, for α-Al 2 O 3 two major types of nitrogen were detected on N 2 + impact; the two N 1s lines were separated by 7 eV The one at 3964 eV binding energy corresponds to a nitride-type N-Al environment, similar to that found in bulk AlN Formation of the nitride is interpreted as the result of replacement of lattice oxygen around Al by implanted nitrogen in a two-stage process The 4034 eV component is assigned to nitrogen trapped in the cation-deficient lattice of α-Al 2 O 3 in empty octahedral sites surrounded by oxygen atoms bonded to Al Both of these chemical states of nitrogen were stable on heating up to 550-650°C