Showing papers on "Chemical state published in 1997"

Native Oxide Layers Formed on the Surface of Ultra High-Purity Iron and Copper Investigated by Angle Resolved XPS

Abstract: Angle resolved X-ray photoelectron spectroscopy (AR-XPS) has been used for characterizing native oxide layers formed on the surface of ultra high-purity iron and copper by exposure to air at room temperature. Thickness of an oxide layer formed on the surface of ultra high-purity iron is found to be thicker than that for ultra high-purity copper in the initial stage of oxidation and almost unchanged by air exposure time. On the other hand, thickness of an oxide layer formed on ultra high-purity copper is found to increase with increasing air exposure time. These results are consistent with spectral information for ultra high-purity iron and copper exposed to air; the chemical state of Fe in the surface of ultra high-purity iron is almost independent of exposure time, whereas the chemical state varies in the surface of ultra high-purity copper by exposure for a long term.

XPS Evidence of Redox Chemistry between Cold Rolled Steel and Polyaniline

Abstract: The electrochemical response of polyaniline (PANI) in its undoped intermediate (emeraldine base, EB) oxidation state coated on cold rolled steel (CRS) or glass substrate has been evaluated by X-ray photoelectron spectroscopy (XPS). The oxidation state of the polymer was determined from the ratio of amine vs imine nitrogen chemical states observed in the N(1s) photoelectron spectrum. A room-temperature air-dried PANI coating cast from NMP solution onto CRS was found to be reduced relative to its as-synthesized, air-stable state. Heating the PANI coated on CRS in the absence of air (165 °C, in ultrahigh vacuum) produced an even deeper reduction, resulting from the transfer of electronic charge to the polymer from the metal substrate. Subsequent brief exposure of this reduced PANI coating to air at elevated temperature (165 °C) reoxidized the PANI to the EB state. Analogous treatment of a PANI coating on glass caused no such change in the oxidation state of the polymer. Unlike steel, which provides a redox c...

Study of chemical state of toxic metals during the life cycle of fly ash using X-ray absorption near-edge structure

Abstract: The non-destructive x-ray absorption near-edge structure (XANES) method was applied to the quantitative determination of chromium and arsenic species in coal fly ash. In order to study the chemical state changes caused by deposition and sedimentation of the particles, land fill and river sediment samples obtained in the neighborhood of power plants were also investigated. The measurements were carried out at the X26 beam line of the BNL National Synchrotron Light Source (USA) in fluorescent mode. For achieving quantitative results on the ratio of close-lying oxidation state forms, a non-linear fitting model was developed to process the XANES spectra obtained. The features of the spectra such as the white line, the multiple scattering resonance peak and the absorption edge were modelled with analytical functions. The results obtained show that chromium is present mostly (>95%) as Cr(III) in fly ash and the chemical state remains the same after deposition and sedimentation. Arsenic is present as As(V) in fly ash and land fill samples, while the possible As(III) content of sediment samples is around 40%. © 1997 by John Wiley & Sons, Ltd.

Substrate Effects and Chemical State Plots for the XPS Analysis of Supported TiO2 Catalysts

Abstract: Tbe analysis by XPS of TiO 2 deposited on different substrates (SiO 2 , MgO, Ag, SnO) shows the existence of shifts in the Ti 2p binding energy and Auger parameter values. The magnitude of these shifts is a function of the support and of the coverage. A systematic representation of these shifts is possible with a chemical state plot. The implications of the existence of such shifts for the characterization of catalysts are discussed.

Changes in the Chemical State and Composition of the Clean Surface of K2CrO4 and K2Cr2O7 due to Air Exposure and Argon Ion Bombardment

Abstract: X-ray photoelectron spectra have been used for characterizing changes in the chemical state and composition of the clean surface of single K 2 CrO 4 (potassium chromate) and K 2 Cr 2 O 7 (potassium dichromate) crystals with Cr(VI) due to air exposure and argon ion bombardment. Their clean surface was prepared by cleaving these crystals in UHV, and XPS spectra from the surface were successfully obtained only by optimizing conditions of the neutralizer because of non-conductivity. The chemical state of constituent elements in the surface of K 2 CrO 4 , and K 2 Cr 2 O 7 was not significantly affected by air exposure, although the surface concentration was changed. On the other hand, argon ion bombardment considerably induced reduction of chromium ions, Cr(VI) to Cr(III), in K 2 CrO 4 , and K 2 Cr 2 O 7 , while the chemical state of potassium and oxygen is almost unchanged by the bombardment. It was also found that the preferential sputtering of potassium in K 2 CrO 4 and K z Cr 2 O 7 takes place during the argon ion bombardment, and the degree of the preferential sputtering in K 2 Cr 2 O 7 is about twice as high as that in K 2 CrO 4 . From the correlation between the variation in the chemical state of chromium and the preferential sputtering of potassium, the reduction behavior of chromium ions by the ion bombardment is considered mainly attributed to the preferential sputtering of potassium from the surface of K 2 CrO 4 and K 2 Cr 2 O 7 crystals. by John Wiley & Sons, Ltd.

Characterization study of GaAs(001) surfaces using ion scattering spectroscopy and x-ray photoelectron spectroscopy

Abstract: A surface characterization study using ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) has been performed on solvent cleaned, n-type GaAs(001) substrates before and after cleaning by ion sputtering and annealing. The native oxide layer on this surface contains large amounts of As2O5,As2O3, and Ga2O3 according to XPS with Ga2O3 being the predominant species. Before cleaning C is present as hydrocarbons, carbonates, and carbide with hydrocarbons as the predominant chemical state. Ion sputtering converts the hydrocarbons into carbide, which is difficult to remove by further sputtering/annealing cleaning cycles, but O is removed by these cycles. According to ISS data, the outermost atomic layer is enriched in Ga before cleaning, but after cleaning the ISS Ga-to-As atom ratio is about 1:2. The results obtained in this study are consistent with the presence of a layered oxide structure with Ga2O3 just above the interface. A sputter-cleaned surface initially exhibits an increase in t...

Chemical reactions induced by the room temperature interaction of hyperthermal atomic hydrogen with the native oxide layer on GaAs(001) surfaces studied by ion scattering spectroscopy and x-ray photoelectron spectroscopy

Abstract: A surface characterization study using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy has been performed on solvent-cleaned, n-type GaAs(001) substrates before and after room temperature exposure to the flux produced by a novel atomic hydrogen source based on electron-stimulated desorption of hyperthermal (∼1 eV) hydrogen atoms. The native oxide layer on the solvent-cleaned GaAs(001) substrate contains C, As2O5 , As2O3 , and Ga2O3 according to the XPS data with Ga2O3 being the predominant species. Before H atom exposure, the C is present as hydrocarbons, carbonates, alcohols, and carbides with hydrocarbons as the predominant chemical state. Upon room temperature exposure to a 1 eV hyperthermal H atom flux, the O in As and Ga oxides is removed, and the amount of C present is reduced through methane formation and desorption. In this process hydrocarbons are not converted to carbides, which are difficult to remove, as in the case of ion sputtering. After reduction the predominant form...

Auger electron spectroscopy study of oxidation behavior of iron and chromium in Zr(Fe,Cr)2 precipitate in zircaloy-4

Abstract: The oxidation behavior of Zr(Fe,Cr)2 precipitates being present at the surface of Zircaloy-4 was examined with microprobe Auger electron analysis, focussing attention on the oxidation behavior of chromium and iron in the early stage of oxidation where the oxide film was coherent. Chromium formed a thin oxide layer at the top surface of the zirconium oxide film of precipitate and remained in a metallic state inside the oxide film. Iron was oxidized via dissolution in the matrix zirconium oxide near the top surface and remained in a metallic state inside the oxide film. Such variety of chemical state of chromium and iron with depth in the oxide film was attributed to the existence of oxygen potential gradient in the oxide film.

Tribological Study of Chemical States of Protective Oxide Film Formed on Steel After Sliding in Humid Atmosphere and in Aqueous Solutions

Abstract: A tribological study of low-carbon steel was carried out in humid atmospheres and in corrosive aqueous solutions (water and 1 percent H2 O2 solution), to determine the chemical states of the protective oxide film and its tribological properties. The chemical states of the oxide film on the slid steel surface were determined using an electron probe microanalyzer. The analytical results showed that the Fe3 O4 layer effectively reduced the friction coefficient, whereas FeO and Fe2 O3 did not. The chemical states and compositions of the oxide film were attributed to the sliding conditions which induced the oxidation tribologically. And the oxide forms remained stable until analysis even in the aqueous solutions. Friction work was a simple and useful parameter for classifying corrosive and mechanical wear on the slid surface.

Electron spectroscopic investigation of polymers and glasses

Abstract: X-ray induced photo and Auger electron spectroscopic techniques have been applied to investigate conducting polymers, their blends and some glasses. In the Nls region of the spectra of films containing polypyrrole the peak corresponding to fl at 402.0 eV is separated from the neutral N. Intensity of the "+ peak can be correlated with electrical conductivity of the films and the spectroscopically derived ratio of F/N+ is close to 4 indicating that one BF4- dopant ion is incorporated for every oxidized nitrogen center. In the spectra of the films of polythiophene and its blends peaks corresponding to S and S+ can not be resolved, but again FIC ratio correlates with the electrical conductivity. On the basis of measured XPS chemical shifts in the binding energies the chemical state of Sn (+2 or +4) incorporated on to the float glasses could not be assigned. Use of the Auger parameter lets one separate relaxation and chemical contributions. The derived true chemical shifts of Sn on float-glasses are larger than those of SnO andor SnO2 due to the larger ionic environment of the glass matrix.

Chemical State of Phosphorus at the Silicon Surface

Abstract: We used synchrotron radiation photoelectron spectroscopy (SRPES) to investigate the chemical state of phosphorus that piles up at the silicon surface covered with a native oxide and found that the piled-up phosphorus does not make bonds with oxygen.

Investigation of the chemical state of copper in Cu/SiO2 composite films by x-ray photoelectron spectroscopy

Abstract: The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 A in the subsurface region and about 50 A in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.

XPS Measurement for the Elements in the Interface between Oxygen Ion Irradiated ZrO2–Y2O3 Films and Iron Substrate

Abstract: Zirconia-yttria films containing 7 wt% Y 2 O 3 were prepared on Fe substrate by rf magnetron sputter deposition followed by 40 keV oxygen ion irradiation at room temperature. A study was carried out to investigate the chemical states of the elements of the film as well as of the Fe substrate within the interface region between the oxygen ion irradiated ZrO 2 -Y 2 O 3 film and the iron substrate by using X-ray photoelectron spectroscopy (XPS). It was found that the Zr oxidized states were reduced from Zr 4+ on the side of the film to Zr 3+ mixed with a small amount of Zr 2+ with depth in the interface region, and the trend of Y was similar to that of Zr, while Fe as the substrate element entered into the interface region where it was oxidized.