Showing papers on "Chemical state published in 1994"

Surface characterization study of the thermal decomposition of ago

Abstract: The changes in chemical states and composition of the surface region of a Ag2CO3 powder at various stages during thermal decomposition have been examined using X-ray photoelectron spectroscopy (XPS...

Altered layer as sensitive initial chemical state indicator

Abstract: XPS techniques are used for a comparative study of ion induced effects in simple oxides (ZrO2, SiO2, TiO2) and complex oxides (ZrSiO4, CaTiSiO5, La2TiO5, PbTiO3). We have found that reduction effects in simple and complex oxides differ. The interpretation of altered layer composition has been qualitatively considered in terms of the preferential loss of oxygen and reverse chemical reactions.

Analytical and electrochemical study of passive films formed on nickel—chromium alloys: Influence of the chromium bulk concentration

Abstract: Depth composition and chemical states of elements constituting the overlayers of NixCr alloys (x = 0–30 at.%) passivated in borate buffer solutions (pH = 9.2) were determined as a function of the chromium bulk content of the alloy. Depth sputter profiling was performed using both Auger electron spectroscopy (AES) and low energy ion scattering spectroscopy (LEIS). Chemical bonding and (oxy-hydroxy) structures of alloying elements in the passive films were investigated by x-ray photoelectron spectroscopy (XPS). The electrochemical study mainly consists in establishing the cathodic reduction kinetics of the passive layers to characterize the resistance of the internal Cr2O3 barrier to reduction. Very thin films (less than 2.5 nm) were obtained in those conditions showing duplex structures where minor external nickel oxy-hydroxide layers are depicted covering an inner protective barrier mainly composed of chromium oxide Cr2O3. Only at high bulk chromium contents (> 15 at.%) are complete Cr2O3 layers built at the interface with the metallic alloy. Beneath the film, in the underlying matrix, a metallic nickel enrichment combined with a chromium depletion is observed, which seems to confirm, as for FeCr alloys, a mechanism by which Cr oxidizes preferentially in this medium during the first steps of the film growth.

Near-Field Optical Microscopy, Spectroscopy, and Chemical Sensors

Abstract: Introduction Optical microscopy and spectroscopy have long been key techniques in medicine, biology, chemistry, and materials science. Among their advantages are: 1. Universality. All materials and samples attenuate light and have spectroscopic states. 2. Noninvasiveness. Most often the sample is not altered in a microscopic and/or spectroscopic investigation. Moreover, biological samples usually can be studied in their native environment. Most chemical reactions are not perturbed by light of long enough wavelength. 3. Real-time observation. Biological phenomena, chemical reactions, crystallization, and so on can be observed under the microscope as they happen in situ (even with one's eyes); spectroscopic measurements can be performed on line in an industrial process or other setting. 4. Energy and chemical state resolution. The obvious advantages of spectroscopy and photochemistry, at ambient temperature, can be trivially added to the optical methods mentioned above. By contrast, this is not easily accom...

(NH4)2Sx‐treated InP(001) studied by high‐resolution x‐ray photoelectron spectroscopy

Abstract: The chemical state of sulfur on (NH4)2Sx‐treated InP(001) surfaces has been studied by high‐resolution x‐ray photoelectron spectroscopy. We find three kinds of chemical states of sulfur (S2p3/2 lines at 161.2, 162.0, and 163.4 eV) on the sample treated at RT. It is suggested that they correspond to sulfur in phosphorus sites (in the second layer of the InP(001) surface), to sulfur bonded to indium on the first layer, and to elemental sulfur on sulfide, respectively. One (S2p3/2=162.0 eV) of them becomes predominant with long‐time exposure to atmosphere at RT. Upon annealing the sample at 400 °C, the 163.4 eV line disappears, while the lines at 162.0 and 161.2 eV remain on the surface. A model of the treated surface is presented.

Surface chemical changes in PVD TiN layers induced by ion bombardment

Abstract: TiN layers produced by the PVD method were subjected to bombardment by different ion species applied in sequence. The relative atomic concentration and the chemical states of the elements in the surface layer were determined by means of x-ray photoelectron spectroscopy. The composition and chemical states of a reference sample after wet chemical etching were taken to be representative for the stoichiometric TiN not affected by ion sputtering. For this sample characteristic line energies of Ti 2p3/2 = 454.7 eV and N 1s = 396.7 eV were found. Alternate bombardment with Ar+, N2O+ ions (1–5 keV) results in significant compositional and chemical state changes. Ar+ bombardment leads to preferential loss of N from the outermost (1–3 nm) surface layers of the nearly stoichiometric TiNx (x = 1.0–1.1) without observable changes in the chemical state of the constituents. Bombardment with N2+ ions leads to a build-up of excess N (x ≫ 1) followed by the appearance of new N 1s and Ti 2p lines at 395.8 ± 0.3 eV and at 456.3 ± 0.3 eV, respectively. N2O+ bombardment increases the O and decreases the N concentration together with a concomitant shot out of a Ti 2p3/2 component peak at about 457.6 eV assignable to Ti2O3.

Secondary ion mass spectrometry time of flight and in situ x‐ray photoelectron spectroscopy studies of polymer surface modifications by a remote oxygen plasma treatment

Abstract: Surface modifications induced by a remote oxygen microwave plasma on three different polymers (LDPE, PS, PMMA) have been extensively investigated in situ by x‐ray photoelectron spectroscopy (XPS) and, after transfer in atmosphere, by time of flight secondary ion mass spectrometry (TOF SIMS). By a direct transfer from the plasma chamber to the XPS spectrometer the chemical functionalities introduced on the surface of the polymeric substrate are identified and quantitatively determined. Furthermore, high resolution molecular analysis by TOF SIMS allows a better understanding of the chemical changes induced by the oxygen plasma. The information gathered from the two techniques permits us to propose oxidation mechanisms of the polymer surfaces. The relative density of ground state atomic oxygen O (3P) in the remote discharge is shown to be of fundamental importance for the initiation of the oxidation. This species is responsible for the formation of radicals from which are further produced highly oxidized fun...

Surface precipitation process of epitaxially grown graphite (0001) layers on carbon‐doped nickel(111) surface

Abstract: The surface precipitation process of epitaxially grown graphite (0001) layers on the C‐doped Ni(111) surface has been investigated by in situ x‐ray photoemission spectroscopy measurements. Peak intensity measurements at various temperatures clarified the change of the carbon chemical state from the segregated carbon through the monolayer graphite to the multilayer graphite. The simple thickness estimation in the transition region from the monolayer graphite to the multilayer graphite indicates that once the estimated thickness is calibrated, controlling the thickness of the graphite thin film in the monolayer range by a precise adjustment of the temperature may be possible. Changes of the chemical states of carbon on the Ni(111) surface with temperature were clarified by high‐resolution measurements with a monochromated Al Kα source. From the observed chemical shift of the C 1s peaks, a negative charge transfer from the monolayer graphite to the substrate can be postulated. This C–Ni interaction is consid...

Dispersion and electronic structure of titania-supported cobalt and cobalt oxide

Abstract: Results from a surface study of titania-supported cobalt are presented. The data show a clear interaction between the Ti(110) support and the overlayer, as a function of thermal treatments and oxidation state. Two model substrates, fully oxidized and partially reduced TiO[sub 2], were impregnated with metallic cobalt or cobalt oxide via dry chemical methods. The resulting four combinations, TiO[sub 2]-o/Co, TiO[sub 2]-o/CoO, TiO[sub 2]-r/Co, and TiO[sub 2]-r/CoO, were compared with reference spectra for the isolated constituents by means of electron spectroscopic measurements following annealing to subsequently higher temperatures. We employ a new fingerprint' technique to analyze the data, thereby allowing us to utilize all available peak positions for a better understanding of chemical interactions and dispersion changes. From our data we can conclude that only metallic cobalt influences the chemical state of titania. The dispersion of CoO changes at moderate temperatures, 500-700 K, but this is restricted to coalescence of the overlayer. The overlayer oxide is less stable on the partially reduced support than on fully oxidized titania. Metallic cobalt, as deposited or from decomposition of CoO, diffuses into titania at above 700 K on TiO[sub 2]-o and above 500 K on TiO[sub 2]-r. This interdiffusion is accompanied by amore » reduction of the support. The lower stability of CoO on the partially reduced support is accompanied by a stabilization of cobalt in the surface region. 52 refs., 10 figs., 1 tab.« less

Chemical States of Implanted Aluminum Ions in Silica and Silicon Ions in Alumina

Abstract: Aluminum and silicon ions have been implanted in silica glass and [alpha]-alumina single crystal, respectively, to doses ranging from 1 [times] 10[sup 15] to 1 [times] 10[sup 17] ions[center dot]cm[sup [minus]2]. The chemical states of these implanted ions have been studied by X-ray fluorescence spectroscopy. It is found that the implanted aluminum atoms are coordinated only by oxygen atoms, irrespective of implantation dose. On the other hand, the implanted silicon atoms are coordinated only by oxygen atoms at low doses and by both oxygen and silicon atoms at high doses. Although the chemical state of the aluminum atoms is unchanged by heat treatment, that of the silicon atoms is changed toward a less positively charged state. It is inferred that the chemical states of the implanted atoms are controlled by the transport process, although these tend to obey the thermodynamic stability.

The chemical environment of nitrogen in the surface of carbon fibres

Abstract: The electrolytic oxidation of Type AU carbon fibres in an ammonium bicarbonate electrolyte was used as a model for the surface treatment of commercially available Type AS fibres. XPS and for SIMS of a range of fibre treatment levels was used to obtain information on the chemical changes at the fibre surface resulting from this treatment. The chemical state of the nitrogen determined by XPS to be present on the surface of Type AU fibre was identified as a protonated amine from the N1s peak position. Nitrogen was introduced into the surface of the Type AU fibre as a result of the electrolytic oxidation process. From a combination of XPS and for SIMS it it postulated that this was present as either an aromatic imide or urethane

Characterization of a-C:H/W and a-C:H/Cr solar selective absorber coatings

Abstract: Tungsten and chromium containing hydrogenated amorphous carbon films were deposited in a process which combines plasma activated chemical vapor deposition of methane and r.f.- sputtering of a metallic target. The metal content of the deposits can be adjusted by the ratio of gas flow between argon and methane and was determined by X-ray Photoelectron Spectroscopy (XPS). For the a-C:H/W composites the XPS data are presented in detail and supply information about the chemical state of carbon and tungsten. The presence of W in carbidic state could be proven. Furthermore the optical constants n and k of a-C:H/W were obtained in the wavelength range between 0.4 and 2.6micrometers and for W concentrations of up to 33 at.%. The morphology of the deposits, determined by atomic force microscopy, ranges from very porous to compact and can be controlled by the substrate bias voltage. Accelerated ageing investigations were performed in air in order to characterize the deterioration mechanisms of a-C:H/W and a-C:H/Cr films deposited on different substrate materials. The significance of the morphology of the coating and the roughness of the substrate for the ageing mechanisms could be shown. Very promising results concerning the film stability were obtained for a-C:H/Cr.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Chemical characterization of environmental particulate matter using synchrotron radiation

Abstract: First results from a new program for chemical characterization of environmental particulates using synchrotron radiation are described. Trace element concentrations and chemical state determinations were made on fly ash samples from lignite-fired power stations. The experiments were based on the use of x-rays produced by an electron beam passing a bending magnet at the Brookhaven National Synchrotron Light Source. The high brilliance, energy tunability and almost complete polarization of the x-rays were used as the basis of a versatile X-ray microscope (XRM) at the X26 beam line. Mossbauer spectroscopy was employed as a complementary method for determination of the compounds in the iron-containing fly ash particles. The results demonstrate the practicality and strengths of using the synchrotron XRM for measurements of trace elements in fly ash particles and for the determination of oxidation states using x-ray absorption near-edge structure.

Co oxidation on LaCoO3 perovskite

Abstract: A study of CO oxidation on LaCoO3 perovskite was performed in an ultrahigh vacuum system by means of adsorption and desorption. All gases were adsorbed at ambient temperature. Two adsorption states (α- and β-) of CO exist. The α-peak at 440 K is attributed to carbonyl species adsorbed on Co3+ ions while the β-peak at 663 K likely comes from bidentate carbonate formed by adsorption on lattice oxygens. CO2 shows a single desorption peak (β-state, 483 K) whose chemical state may be monodentate carbonate. A new CO2 desorption peak at 590 K can be created by oxidation of CO. O2 also shows two adsorption states. One desorbs at 600 K, which may reflect adsorption on Co3- ions. The other apparently incorporates with bulk LaCoO3 and desorbs above 1000 K. The two adsorption states of CO are oxidized via different mechanisms. The rate determining step in oxidation of a-CO is the surface reaction whereas for that of β-CO, it is desorption of product CO2.

Microscopic characterization and electrochemical behavior of high-dose carbon-implanted stainless steels

Abstract: A study was made of the electrochemical properties and microscopic characteristics of types 304 and 430 stainless steel implanted at room temperature with carbon at a dosed of 1018 ions cm-2 at 100 keV. The electrochemical properties were measured by multisweep cyclic voltammetry in a solution of H2SO4 + Na2SO4. X-ray diffraction and X-ray photoelectron spectroscopy were used to analyze the structure, composition depth profiles and chemical bonding states of carbon-implanted layers. Carbon implantation suppressed the dissolution with transpassivation of stainless steels without influencing adversely their excellent passivity. The amorphized carbon-implanted layers were composed of graphitic solid state carbon, which had a gaussian depth profile corresponding to the distribution of implanted carbon, and metallic carbide with a uniform chemical state in the region containing more than approximately 20 at.% carbon. From these investigations, it is proposed that room-temperature carbon implantation at a very high dose can improve the aqueous corrosion resistance of stainless steels owing to the formation of amorphous layers consisting of graphitic solid state carbon and metallic carbide.

X-ray absorption spectroscopy study of the local structure and the chemical state of yttrium in polycrystalline α-alumina

Abstract: The chemical state and local structure around the yttrium ion in doped polycrystalline α-alumina (0·03 <- mol% Y2O3 <- 1) system was examined by extended X-ray absorption fine structure (EXAFS) measurements for yttrium K-edge energy. In the case of highly doped alumina samples (0·1 and 1 mol% Y2O3) most of the yttrium is precipitated as a Y3Al5O12 phase, whereas in the dilute doped alumina sample (0·03 mol% Y2O3) yttrium is in solid solution, being located on the octahedral aluminium sites. The yttrium ion size, comparatively greater than that of the aluminium ion, induces locally a significant distortion of the oxygen ion lattice. This effect creates point defects in the nearest neighbour shell of the yttrium: vacancy (Vo) and interstitial (Oi′) oxygen point defects.

Dielectric characteristics and chemical structures of Nb2O5 thin films grown by sol-gel techniques

Abstract: Nb2O5 thin films were produced on silicon substrates by sol-gel spin-coating technique. The films were heat-treated at temperatures ranging from 600°C to 1000°C in oxygen atmosphere, and their crystalline phases, chemical states, and dielectric characteristics were investigated by X-ray diffractometry (XRD), Auger electron spectroscopy(AES), and C-V measurements, respectively. The Nb2O5 thin films annealed at temperatures ranging from 600°C to 1000°C as well as the powders annealed in the temperature region from 600°C to 800°C are of the T-type structure, while the powders annealed at 1000°C are of the H-type structure. The films heat-treated at temperatures ranging from 600°C to 800°C exhibit dielectric constants of less than 20, while the films annealed at 1000°C show a dielectric constant of 28.

Chemical states of implanted ions in an oxide crystal

Abstract: The chemical states of implanted copper and bismuth in an oxide crystal were investigated by using X-ray photoelectron spectroscopy (XPS). Metal ions were implanted into semiconductive strontium titanate single crystals with a fluence of 1 × 1016 ions/cm2 at an energy of 150 keV. Subsequently oxygen ions were implanted with the appropriate fluences and energies to fit the depth profiles to those of implanted metals. Chemical states of ions were determined by XPS with sputter-etching. The state of implanted Cu which was Cu0 in the as-implanted sample could be changed to Cu1+ by the post-annealing at 800°C in air or by the co-implantation of oxygen. The state of implanted Bi which was Bi0 in the samples as-implanted, post-annealed, and oxygen co-implanted could be changed to Bi3+ by the co-implantation of oxygen followed by heating. Electrical properties were also measured.

X-ray photoelectron spectroscopy study of zirconium-implanted iron and carbon-implanted zirconium

Abstract: A study has been made of the chemical bonding states of zirconium-implanted iron and carbon-implanted zirconium. Ion implantations were carried out at an energy of 100 keV with fluences of 5 × 1016 Zr ions cm-2 and 1.5 × 1016 C ions cm-2. The depth profile and chemical states of elements were investigated by X-ray photoelectron spectroscopy combined with Ar+ sputtering. In the case of zirconium implantation into iron oxide, the Zr 3d 5 2 peak observed on the surface appears at a binding energy of 181.9 eV. Considering this value and the binding energy of Fe 2p 3 2 spectra, zirconium on the surface seems to be bound to oxygen and iron. In the interior, the Zr 3d 5 2 peak shifts to 179.3 eV corresponding to Zr-C and the Fe 2p 5 2 peak also shifts to 706.6 eV corresponding to Fe-C. The binding energy of C 1s appears at 282.0 eV, which corresponds to an intermediate state between C-Fe and C-Zr. These chemical states of Zr, Fe and C indicate the formation of some complex states in implanted layers, associated with ZrxFeyCz.

Thermally Stimulated Desorption Measurements of Heavily Phosphorus-Doped Silicon Surfaces with a Very Thin Oxide Film

Abstract: Heavily phosphorus-doped silicon wafers were prepared by the Shiraki method as a chemical treatment. The thermally stimulated desorption (TSD) from these samples with thin oxide films was studied by using Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and mass spectroscopy. The chemical states of the etched surfaces were measured by X-ray photoelectron spectroscopy (XPS). It was found that the thin oxide film on the doped polycrystalline Si surface was desorbed easily at relatively low temperature (560°C), similarly to a single-crystal one. The desorption of the oxide is due to the chemical state from the interface to the near-surface region which includes not only SiO2 but also SiOx. For a single-crystal silicon, a large quantity of phosphorus segregated to the near-surface region even after the oxide had desorbed. It is considered that this phosphorus segregation is attributable to the existence of the strain which is not relaxed because of the low annealing temperature even after desorption of the oxide.

XPS and AES study of Al2O3/Ti6Al4V interface: Influence of oxidation and nitruration of the metal surface

Abstract: Important properties of the coating/substrate combination like hardness, stress and, in particular, adhesion rely partly on the morphology and microstructure of the interface, which is often physically and chemically different from the substrate as well as from the coating. The aim of this work is to study the influence of the chemical state of the metal surface on the structure of the interface Al 2 O 3 /Ti6Al4V, obtained by deposition via sputtering of the ceramic. For this purpose three different surface treatments of the substrate were performed: air oxidation, cleaning by Ar + sputtering and nitrogen ion implantation