Showing papers on "Chemical state published in 2002"

XPS, XANES and EXAFS investigations of CuO/ZnO/Al2O3/ZrO2 mixed oxide catalysts

Abstract: Systematic X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (AES), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were undertaken to investigate the electronic structure, chemical states and local geometry of the active species in the CuO/ZnO/Al2O3/ZrO2 multicomponent mixed oxide catalysts employed in the oxidative steam reforming of methanol (OSRM) reaction for H2 production. The core level XPS and AES indicated the existence of CuO and ZnO-like species. Two kinds of zirconium species, one similar to that of ZrO2 and another with relatively higher electron density were noticed from the Zr 3d core level XPS of Zr- containing catalysts. The valence band (VB) XPS studies revealed that for Zr-containing catalysts, the Cu 3d anti-bonding orbital splits from the main VB and shifts toward lower binding energy (BE). The surface Cu/(Al + Zr) ratios were found to be close to those in the bulk while segregation of Zn at the surface was evidenced in all samples. The XANES and EXAFS results also indicated the existence of CuO and ZnO-like species, whose local environments are modified with respect to the chemical composition. The EXAFS study of the Zr-containing catalysts indicated the existence of a “Cu–O–Zr” bonding with a Cu–Zr distance in the range 3.5 to 3.9 A. The results indicated the existence of a Cu–Zr synergistic interaction in these catalysts which improved the catalytic performance in the OSRM reaction

Ablation of noble metals in liquids: a method to obtain nanoparticles in a thin polymeric film

Abstract: Pulsed laser ablation of gold and silver in several liquids (mainly water, ethanol and chloroform) has been studied to obtain nanoparticle sols using a 532 nm, 5 ns radiation. We observed the formation of metallic and non-metallic particles in the nanometre size range depending on the liquid used as environment. The chemical state of the formed nanoparticles depends mainly on the chemical reactivity of the liquid. Here we demonstrate the possibility of using this method to obtain nanocomposite polymer films.

A Study on the Chemical Forms and Migration Behavior of Carbon-14 Leached from the Simulated Hull Waste in the Underground condition

Abstract: The chemical forms of carbon leaching from carbon-containing Zr and Fe-based metallic materials have been investigated to improve the estimation of the contribution of C-14 in the performance assessment of TRU waste disposal. Both organic and inorganic carbons were identified in the leached solution with carbon containing zirconium and steel, and the concentrations of total carbon (organic plus inorganic) in the leached solutions increased with time. The carbon concentrations in the leached solution for both metallic samples were higher at higher pH. With High Performance Liquid Chromatography (HPLC), organic carbons were identified to be low-molecular weight alcohols, carboxylic acids and aldehydes. To explore the chemical state of carbon in the matrix materials, the leaching experiments were carried out also for ZrC, Fe3C, the powder mixtures of carbon and zirconium, and of carbon and iron. The low-molecular weight organic carbons were detected only in the case of carbides (ZrC and Fe3C). The chemical forms of carbon in the zirconium alloy were suggested to be carbide or carbon by H.D. Smith[1]. The present result suggests that the chemical forms of carbon in zirconium or iron are mainly in the form of carbide. In the interest of performance assessment, the distribution coefficients of the organic carbon species identified in the leached solution for cement were obtained. As expected, some of them were shown to be larger than the values assumed in the performance assessment of Progress Report on Disposal Concept for TRU Waste in Japan[2].

XPS Applications in Thin Films Research

Abstract: XPS (X-ray Photoelectron Spectroscopy) or ESCA (Electron Spectroscopy for Chemical Analysis) as a surface analytical technique has been developed over years and has been used successfully in characterization of a variety of thin films. Information such as composition, chemical states, depth profile, imaging and thickness of thin films is especially useful in thin film research. This paper aims at reviewing these applications of XPS in thin film area.

Surface chemical changes induced by low-energy ion bombardment in chromium nitride layers

Abstract: In this work three types of CrN x layers-one close to Cr 2 N, the other to CrN and a third with high nitrogen content CrN 1+x - were prepared by reactive magnetron sputtering. The samples were subjected to bombardment by Ar + and N 2 + ions applied in sequence. The relative atomic concentration and the chemical states of the elements in the surface layer were determined by x-ray photoelectron spectroscopy. Alternate bombardment with Ar + and N 2 + ions (1-2 keV) resulted in significant compositional and chemical state changes. Although prolonged Ar + bombardment did not decrease the nitrogen content of Cr 2 N below the nominal (CrN 0.5 ) composition, it decreased the nitrogen content of the closely stoichiometric CrN appreciably, to about CrN 0.8 . At bombardment with N 2 + ions nitrogen could be implanted into the Cr 2 N films, changing its composition up to about CrN 0.8 . It was shown that extra nitrogen could be incorporated also into the CrN samples, increasing the nitrogen content above the stoichiometric composition up to about CrN 1.2 . The CrN 1+x -type sample showed high stability towards Ar + bombardment. Two significantly different chemical states of nitrogen were determined for the two types of nitrides: the N is peak at 397.5 ± 0.1 eV binding energy was characteristic of N in Cr 2 N and the peak at 396.5 ± 0.1 eV of N in the CrN state. The effect of Ar + and N 2 + bombardment on the surface composition discussed in this paper may provide information for elaboration of deposition conditions for CrN x coatings with predetermined chemical composition and structure.

Characterization of the interface in rubber/silica composite materials

Abstract: In the rubber industry, especially tyre production, the most widely used elastomer is styrene-butadiene rubber (SBR) in which the styrene units generally are present at 25 wt.%. The unit repeats are random distributed along the macromolecular chains and the configuration of the butadiene units is mostly 1,4-trans. The elastomer blends are mixed with fillers, acting as reinforcing agents, and the effect that silica particles have on their physical and mechanical properties is now well established. One of the most important parameters in determining the performance of such composite materials is the degree of adhesion at the rubber/silica interface. In this context, the interface characterization has been performed through a spectroscopic investigation (XPS/x-ray-induced Auger electron spectroscopy) in order to derive information from core-level and Auger line chemical shifts. A series of composite rubbers have been examined by means of a detailed curve-fitting procedure that allows the determination of intrinsic and extrinsic structures connected to each photopeak and the spectroscopic results compared with those of reference compounds. The changes in the C 1s lineshape and shake-up region of the polymers and the reduced binding energies of silicon, oxygen and sulphur core lines have provided clear evidence of interfacial reactions. Moreover, the Auger parameters of silicon show systematic shifts that can be interpreted on a chemical state plot in terms of initial- and final-state contributions and used for theoretical investigation of the local chemical environment.

Chemical state speciation by resonant Raman scattering

Abstract: In the resonant Raman scattering (RRS) process the emitted photon exhibits a continuous energy distribution with a high energy cutoff limit. This cutoff energy depends on the chemical state of the element under examination. In the present work, the possibility of identifying the chemical state of V atoms by employing RRS spectroscopy with a semiconductor Si(Li) detector is investigated. A proton induced Cr Kα x-ray beam was used as the incident radiation, having a fixed energy lower than the V K-absorption edge. The net RRS distributions extracted from the energy dispersive spectra of metallic V and its compound targets were simulated by an appropriate theoretical model. The results showed the possibility of employing RRS spectroscopy with a semiconductor detector for chemical speciation studies.

High-resolution X-ray spectroscopy for copper and copper oxides and a new WDX system using an ion microbeam

Abstract: High-resolution Cu L X-ray spectra from Cu, Cu2O and CuO targets induced by MeV H, He, C and F ions have been measured. High-resolution Cu Lα1,2 and Lβ1 X-ray spectra from Cu, Cu2O and CuO targets induced by 2.0 MeV focused protons have been also measured. It is shown that high-resolution X-ray spectra are sensitive to the chemical states of the emitting projectile and target atoms. The Cu Lα1,2 and Lβ1 X-ray spectra were compared with Cu 2p XPS spectra to investigate the atomic and electronic structures and electron excitation and relaxation processes in Cu and its compounds. High-resolution X-ray spectroscopy with a microbeam is found to be useful for analysis of the chemical environment of atoms of interest in the near surface region of bulk and particle samples.

Micro-XPS analysis of slide-tested TiN films with/without Cl+ implantation.

Abstract: We analysed the surface of TiN films (∼2 μm thick) with/without Cl + implantation by scanning XPS. Both TiN films were subjected to a sliding test by a stainless-steel ball, resulting in round, 150 μm wide scratches on the surface. We examined the difference in chemical composition and chemical state between the worn and the unworn surfaces. On the TiN film without Cl + implantation, the primary compounds found were TiO 2 and TiN with carbon contamination. The friction coefficient was ∼0.8 on this surface. The chemical compound on the worn surface was mainly Fe 2 O 3 with a small amount of TiO 2 . This suggests that TiN is hard but not lubricative and that elements from the stainless-steel ball adhered to the surface of the TiN film during the sliding test. On the TiN film with Cl + implantation, the main compound found was TiO 2 , although we also observed a small amount of TiN. Furthermore, we detected a small amount of Cl, whose chemical state indicated binding with a metal component. The friction coefficient was <0.2 on this surface. The chemical compounds on the worn surface were TiN and TiO 2 , and no Fe was detected. We could clearly detect TiO 2 on the surface of the stainless-steel ball, therefore we concluded that oxidation is enhanced on Cl + implanted TiN and that titanium oxide functions as a lubricant. During the sliding test, oxidation of the TiN film seemed to continue and titanium oxide was supplied continuously.

The nature of chemical species in novel antimicrobial silver films deposited by magnetron sputtering

Abstract: As part of a broad multidisciplinary investigation to elucidate the role of chemical speciation in biological efficacy, novel silver films exhibiting antimicrobial behaviour were produced by magnetron sputtering a pure silver cathode. These physically vapour-deposited films, grown using a range of gas compositions, gas pressures and input powers, were studied in situ and ex situ using X-ray photoelectron spectroscopy (XPS), in both the as-deposited and the annealed condition. In the in-situ case, a special system was employed to transfer the sample to the analytical chamber of the XPS without exposure to the ambient environment. On the basis of the data obtained, it is postulated that oxygen species detected in the films are present in several chemical states. Furthermore, silver films deposited under specific process conditions exhibited antimicrobial behaviour in laboratory biological tests. The unique antimicrobial properties are explained in terms of the bulk composition, microchemistry and c...

The structure, composition, and chemical state of the surface of wire-like silicon nanocrystal grown by self-organization technology

Abstract: The surfaces of wire-like silicon crystals grown by self-organization processes are characterized using electron microscopy of high resolution, scanning tunnelling microscopy, x-ray microprobe analysis, secondary-ion mass spectroscopy, and Auger electron spectroscopy. The results obtained have shown that the upper layer of each microcrystal is a nanoporous envelope. The composition of the envelope is in general similar to the composition of the bulk part of the crystal but with some differences: the density of the matter - due to the porous nature of the envelope - is much smaller, and the density of metal impurities is slightly increased on the external surface. More striking was the fact that the external surface of the envelope is passive under exposure to oxygen. In Auger spectra of crystals stored in open air for several years, only the LVV and KLL peaks that are specific to the atomically clean silicon surface were observed.

Changes in the Chemical State and Composition of the Surface of Iron Oxides due to Argon Ion Sputtering

Abstract: XPS has been used for investigating the influence of argon ion sputtering on the chemical state and composition of the surface of three iron oxides, Fe2O3, Fe2NiO4 and Fe2ZnO4. XPS spectra of these oxides were measured, while bombardment by argon ions of 3keV were interrupted. The chemical state of the surface of these oxides was found to change from Fe3+ to Fe2+ by argon ion bombardment, suggesting the reduction of the surface of these oxides. This behavior was attributed to a decrease of the oxygen composition of the surface of these oxides. Then, particular attention should be paid in analysis of a layered structure of oxides formed on the iron and steel surface.

Interaction of NH3 and oxygen with Cu(1 1 0), investigated by FT-IRAS

Abstract: Adsorption of ammonia, on the Cu(1 1 0) surface, has been investigated in situ, at room temperature, by Fourier-transformed infrared reflection–absorption spectroscopy (FT-IRAS). The role of oxygen in the reaction of oxy-dehydrogenation of ammonia was made clear by successively characterising the interaction of ammonia, co-adsorbed with oxygen on metallic Cu(1 1 0) or adsorbed on an oxygen-pre-dosed Cu(1 1 0) surface. Auger electron spectroscopy was used to check the chemical state of the surface after oxygen and/or ammonia exposure. NH 3 was observed to adsorb in a molecular form on the metallic Cu(1 1 0) surface. When co-adsorbed with ammonia or pre-adsorbed on the surface, oxygen favours abstraction of hydrogen from NH 3 , eventually yielding dinitrogen.

A study of alumina thin films grown by low pressure mocvd: xps and aes

Abstract: We have studied the chemical composition of alumina (Al2O3) films grown on Si(100) at different substrate temperatures by metalorganic chemical vapor deposition (MOCVD) using aluminium acetylactonate {Al(acac)3} as the precursor. We have found that the resulting films of Al2O3 contain substantial amounts of carbon. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical state of carbon present in such films. The XPS spectrum reveals that the carbon present in Al2O3 film is graphitic in nature. Auger electron spectroscopy (AES) was employed to study the distribution of carbon in the Al2O3 films. The AES depth profile reveals that carbon is present throughout the film. The AES study on Al2O3 films corroborates the XPS findings. An investigation of the Al2O3/Si(100) interface was carried out using cross-sectional transmission electron microscopy (XTEM). The TEM study reveals textured growth of alumina film on Si(100), with very fine grains of alumina embedded in an amorphous carbon-containing matrix.

Use of the absolute Auger parameter for vanadium in the study of the dielectric relaxation of cerium vanadate

Abstract: X-ray photoelectron spectroscopy (XPS) is known, mainly, as a technique for surface analysis. It is especially valued for interpretation of the chemical state by means of the chemical shift. This paper concerns the contribution to this shift from polarization of the ligands following core photoionization. Intercalation of ions such as lithium will influence the electronic polarizability of the oxygen ions and hence the value of the Auger parameter (AP). The AP is the difference in kinetic energy of the Auger peak in the spectrum and that of the principal photoelectron peak, calculated by an internationally accepted procedure. Thus, while obtaining the composition and chemical state of a compound one can also determine the polarizability of the material. Polarizability is crucial to the dielectric properties of oxides, such as refractive index, and is of value in optimizing intercalation compounds for use in optoelectronic devices. The use of this methodology will be illustrated using the vanadium ion in V2O5 and CeVO4, including its lithium-intercalated form. Copyright © 2002 John Wiley & Sons, Ltd.

Chemical state sensitivity by PIXE, using solid state detectors

Abstract: With accurate analog and digital signal processing, the stability of an X-ray line in a typical spectrum can be as good as 0.3 eV given appropriate precautions. In contrast, newly available atomic binding energy databases indicate that the difference between the Kα and Kβ X-ray energies can range over several eV, depending on the chemical state of the emitter element. In addition the Kβ ′ satellite structure varies significantly in energy and intensity depending on chemical state. It follows that PIXE spectra cannot be fitted with optimal accuracy if the database does not recognize these effects. On the positive side, it now appears worthwhile to investigate the possibility of deducing chemical information from the Kα–Kβ separation in PIXE spectra.

Rapid chemical state analysis by a highly sensitive high-resolution PIXE system

Abstract: We have developed a crystal spectrometer system for rapid chemical state analysis by external beam particle induced X-ray emission. The system consists of a flat single crystal and a five-stacked position-sensitive proportional counter assembly. Chemical state analysis in atmospheric air within several seconds to several minutes is possible. A mechanism for time-resolved measurements is installed in the system. Performance of the system is demonstrated by measuring the time-dependence of chemical shifts of sulfur Kα1,2 line from marine sediment and aerosol samples.

X-ray Absorption Spectroscopy on Copper Trace Impurities on Silicon Wafers

Abstract: Trace metal contamination during wet cleaning processes on silicon wafer surfaces is a detrimental effect that impairs device performance and yield. Determining the chemical state of deposited impurities helps in understanding how silicon surfaces interact with chemical species in cleaning solutions. However, since impurity concentrations of interest to the semiconductor industry are so low, conventional techniques such as x-ray photoelectron spectroscopy cannot be applied. Nonetheless, chemical information on trace levels of contaminants can be determined with x-ray absorption near edge spectroscopy (XANES) in a grazing incidence geometry. In this study, silicon samples were dipped in ultra pure water (UPW) and 2% hydrofluoric (HF) solutions with copper concentrations of 5 and 1000 ppb, respectively. These samples were then analyzed using XANES in fluorescence yield mode to determine the oxidation state of deposited copper contaminants. It was found that copper impurities on the silicon surface from HF solution were metal in character while copper impurities deposited from the spiked UPW solution were deposited as an oxide. These results show that XANES can provide information on the chemical state of trace impurities even at surface concentrations below a few thousandths of a monolayer.