Showing papers on "Chemical state published in 1989"

Reduction of oxides of iron, cobalt, titanium and niobium by low-energy ion bombardment

Abstract: Ion-beam bombardment of solid surfaces with rare gas ions is used extensively in conjunction with XPS and AES for surface cleaning and depth profiling. It is sometimes not appreciated that the process can give rise to extensive chemical changes in the surface to be examined. The purpose of this investigation is to study this ion-induced chemical damage. As a vehicle for this, changes in the elemental chemical states associated with some transition metal oxides have been examined using XPS, when the oxides were subjected to progressive periods of argon ion bombardment. Chemical reduction of all oxides investigated has been observed and the data have been compared with theoretical predictions from a current model for preferential oxygen removal. Measurements of the core electron energy levels in oxides and some hydroxides of iron, cobalt, titanium and niobium have been made and the results are tabulated.

Surface analysis method and apparatus

Abstract: Described is a surface analysis method for analyzing energy of particles such as photoelectrons which are emitted from a sample surface by the irradiation of light with wavelengths ranging from the soft x-ray region to the vacuum ultraviolet region using an optical system including a reflective optical element to the sample surface so as to obtain chemical state information about the sample surface, wherein the beam diameter of the light on the sample surface is reduced to 1 μm or less in terms of full width at half maximum of the beam intensity profile on the sample surface so that the chemical state information about the sample surface can be obtained with high sensitivity and high resolution, and an apparatus for implementing this method.

The Role of Alloyed Molybdenum in the Dissolution and the Passivation of Nickel‐Molybdenum Alloys in the Presence of Adsorbed Sulfur

Abstract: The authors discuss the effects of Mo on the dissolution and the passivation of a Ni-2 atom percent (a/o) Mo(100) alloy in 0.05M H/sub 2/SO/sub 4/ investigated with or without adsorbed sulfur. Sulfur was preadsorbed on the alloy surface in H/sub 2/S-H/sub 2/ gas mixtures. Complete monolayers of S (i.e., 43 X 10/sup -9/ g/cm/sup 2/) were formed with pH/sub 2/ = 2 X 10/sup -4/ and T = 600{sup 0}C. The surface coverages by sulfur were measured using the sulfur 35 radioisotope (/sup 35/S) and the chemical state was analyzed by electron spectroscopy for chemical analysis. Potentiodynamic and potentiostatic measurements were performed, and the concentration of sulfur on the surface was measured as a function of the amount of dissolving molybdenum. The effect of S is found to be very weak compared to the one previously observed on Ni and Ni-Fe alloys, which shows that molybdenum counteracts the detrimental effects of adsorbed sulfur.

Electronic structure of BaO/W cathode surfaces

Abstract: The local electronic structure of the emissive layer of barium dispenser thermionic cathodes is investigated theoretically using the relativistic scattered-wave approach. The interaction of Ba and O with W, Os, and W-Os alloy surfaces is studied with atomic clusters modeling different absorption environments representative of B- and M-type cathodes. Barium is found to be strongly oxidized, while oxygen and the metal substrate are in a reduced chemical state. The presence of oxygen enhances the surface dipole and Ba binding energy relative to Ba on W. Model results for W-Os alloy substrates show only relatively small changes in Ba and O for identical geometries, but very large charge redistributions inside the substrate, which are attributed to the electronegativity difference between Os and W. If Os is present in the surface layer, the charge transfer from Ba to the substrate and the Ba binding energy increase relative to W. Explanations are offered for the improved electron emission from alloy surfaces and the different emission enhancement for different alloy substrates. >

Bulk and surface characterization of supported cobalt–copper catalysts active in CO hydrocondensation

Abstract: We report the results of the characterization of three cobalt–copper catalysts, supported respectively on MgO, CeO2 and ZrO2 and exhibiting different selectivity behaviour in the production of higher alcohols from synthesis gas. The local composition of the catalyst has been analysed by STEM and the surface state studied by FTIR spectroscopy of adsorbed CO. The results deduced from the STEM analysis show that each metallic particle has a global composition close to the nominal one. By contrast, i.r. data indicate large changes in surface compsition and chemical state. Thus, the surface is constituted for metallic cobalt for the CoCu/CeO2 system, principally of copper when the support is MgO, but is composed of both metallic cobalt and copper for the Co–Cu/ZrO2 catalyst. These results are discussed in relation to the catalytic properties, In particular, it seems that a high selectivity in higher alcohols requires metallic sites constituted of both cobalt and copper.

XPS studies on passivated and degraded YBa2Cu3O7−x films

Abstract: High-temperature YBa 2 Cu 3 O 7 − x superconductors are known to degrade in the presence of moisture. It was shown that the use of certain polymeric materials in solution during processing of the superconductor could passivate the film and reduce degradation in the macroscopic scale. X-ray photoelectron spectroscopy was used to study the surfaces of passivated as well as degraded YBa 2 Cu 3 O 7 − x samples. In the degraded sample, Y, Ba, Cu and O were present in chemical states other than those expected in superconductors. Segregation of Ba at the surface was also observed. In the passivated sample, superconducting species were retained at the surface despite limited impurity build-up.

Analysis of metallic components in zinc phosphate films using electron spin resonance and X-ray fluorescence

Abstract: Hopeite films are generally formed as Zn 3 (PO 4 ) 2 ·4H 2 O on galvannealed steel sheet, but the films also include manganese or nickel if the zinc phosphate solution contains Mn 2+ or Ni 2+ . Although these films are very effective in controlling the corrosion properties of base metals and these additional metallic components considerably improve the adhesion between paint films and base metals, the chemical structural states of these components in the crystalline films were unknown. These states were analysed by means of electron spin resonance (ESR). No ESR signal is observed for hopeite films in which zinc is the only metallic component, because the zinc(II) in the films has an electronic state of 3d 10 . In contrast, manganese and nickel components in the films give ESR signals. The spectrum of the manganese components showed six peaks and indicated that the manganese is present as Zn 3- x Mn x (PO 4 ) 2 · 4H 2 O. The spectrum of the nickel component was also observed and its pattern was similar to that of Ni 3 (PO 4 ) 2 ·7H 2 O. However, the g values, which correspond to the chemical states, were different from those of Ni 3 (PO 4 ) 2 ·7H 2 O. It was thought that the nickel component in hopeite films is present as Zn 3- x Ni x (PO 4 ) 2 ·4H 2 O similar to the manganese component. Furthermore, X-ray fluorescence data also indicated (by the 2θ locations) that the nickel component is not in the metallic state of Ni 0 . In this research it was confirmed that ESR was a very effective and valuable method for characterizing the metallic components in zinc phosphate films.

Composition and chemical states of the plasma anodised film on Ge

Abstract: Anodisation of a germanium surface was carried out successfully in oxygen plasma excited by a high-frequency (500 kHz) electromagnetic field in a quartz reactor. The refractive index of the oxygen plasma anodised (OPA) film on Ge(111) is generally 1.66-1.68 ( lambda =6328 AA). The chemical composition and chemical states of the Ge-OPA film have been analysed using Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) with argon ion sputtering. There is GeO2 on the surface of the OPA film. In the bulk of the OPA film, there is mainly GeO2 and some unoxidised germanium. The distribution of O and Ge is fundamentally homogeneous in the bulk. There are double peaks for Ge(3d) in the XPS of the Ge-OPA film after argon ion sputtering. The binding energy of 32.7 eV is due to the Ge in GeO2, and that of 29.2 eV corresponds to a few unoxidised Ge atoms in the OPA film. The chemical stoichiometry of the OPA film is very similar to that of vitreous GeO2.

Auger parameter and chemical state plots for copper- and zinc-containing compounds: charge distribution and screening effects

Abstract: Cu- and Zn-containing compounds are characterised making use of the Wagner Auger parameter and of the so-called chemical state plots to obtain information on the relative initial-state charge distributions and on the relative extra-atomic relaxation energy. The position in the plots of different classes of compounds is discussed. To explain the constancy of the Auger parameter for Cu(II) compounds and metallic Cu, it is suggested that the energy involved in the electron transfer 2p53d10L is similar to the screening energy in the metallic state.

Study of the low‐pressure chemical‐vapor‐deposited tungsten‐silicon interface: Interfacial fluorine

Abstract: Single‐crystal silicon 〈100〉 substrates uniformly doped at ≳12 Ω cm with boron were deposited with ∼800 A of low‐pressure chemically vapor deposited W in a hot‐quartz‐walled (Anicon) system at a deposition temperature of 300 °C. The samples studied include an as‐deposited sample and two others which were post‐deposition annealed at 600 °C in Ar for 15 min each. X‐ray photoelectron spectroscopy (XPS) coupled with an Ar+ ion sputter profiling technique was employed to investigate these structures as a function of depth. Particular emphasis was placed on the depth distribution, content, and chemical state of the fluorine present. Rutherford backscattering spectrometry and x‐ray diffraction were used to corroborate the XPS data. Results show that, for the as‐deposited and 600 °C annealed sample, the maximum concentration of fluorine (0.6–0.8 at. %) is observed, not at the W/Si interface, but rather at the W (H2 reduction)/W (Si displacement) interface. For the sample annealed at 850 °C, WSi2 is formed in the ...

Quantitative electron-probe microanalysis of light elements: Determination of a -Si∶C∶N∶O∶H insulating films

Abstract: Amorphous Si∶C∶N∶O∶H films (1–3 μm) are studied by EPMA after deposition of gold (1–5 nm) as a conductive coating. Its influence on thek-ratios (X-ray intensity relative to an uncoated standard) of silicon, carbon, nitrogen and oxygen is described as a linear function of the simultaneously determinedk-ratio of gold. Thek-ratios representing the uncoated specimen are obtained by extrapolation and, in combination with the PAP matrix correction model, quantitative EPMA can be performed with an analytical error of 2–5%, as it is demonstrated by samples of SiC, Si3N4 and SiO2. No systematic shift of the concentrations is observed for layers ofa-Si∶C∶N∶O∶H determined at various electron energies of 5–12.5 keV. Hydrogen is calculated by difference and the concentrations prove to be a useful estimate in agreement with the results of chemical analysis. Si-Kβ/Si-Kβ′ spectra recorded on organo-silicon films and binary silicon compounds point out significant differences concerning the formation of Si-C, Si-N and Si-O chemical bonds.

Interaction between S-organic compounds and iron surfaces

Abstract: Detaching of organic polymer coatings as a consequence of a corrosive attack of the substrate material means as serious problem for corrosion protection [1]. Because of the coating thickness and the complex nature of practical corrosion protection systems, direct studies of the phase boundary metal/coating are impossible up to now. Therefore, the mechanism of deadhesion is largely unknown, The aim of this work now is to produce a strong chemical bond between the metal surface to be protected and selected organic monomers (concept of chemically modified metal surfaces [2]). This bond should be stable against aggressive media like strong acid or basic electrolytes. The thickness of the adsorbed organic film is only that of several molecular layers. Therefore, the binding conditions at the phase boundary can be investigated with electron spectroscopic (AES, XPS) and electrochemical (cyclovoltammetry, rotating ringdisk-electrode) methods. Up to now these studies are restricted to the interaction of n-decanethiol (n-DMc) with polycrystalline iron surfaces of different conditions. At room temperature n-DMc is a water like liquid. A first preparation technique means to drop the organic liquid without any further solvent onto the air formed oxide on top of the iron surface covered by a contamination layer. Within a second method the organic liquid is used as a second phase on top of an aqueous acid electrolyte (1 tool/1 HC10,). The sample is removed from the electrolyte at conditions that stabilize metallic iron and is passed through the n-DMc layer. At the phase boundary organic liquid/electrolyte the thiol molecules are oriented in such a manner that the polar (SH)-groups look into the electrolyte. By this a coupling of the sulphur to the metallic substrate occurs when the iron substrate passes the phase boundary. The same procedure is also performed under anodic conditions, so that a surface oxide is stabilized. The results of the surface analytical studies can be summarized as follows: For the oxide free surface the intensity ratios of the Auger peaks of carbon (CKLL) and of sulphur (SLMM) in the freshly prepared state and during Ar+-ion sputtering prove that the preferred orientation of the organic molecules at the phase boundary organic liquid/electrolyte is transferred to the chemisorbed molecules. The thiol binds to the metallic iron surface by the mercapto group (-SH). The aliphatic chains are oriented more or less perpendicular with respect to the surface. For preoxidized and contaminated iron surfaces the dropping technique results in a statistical arrangement within the thiol film. By modifying the iron substrate under anodic conditions only traces of n-DMc could be adsorbed on the oxidized surface and no further investigations were performed for these samples. The sensitivity of adsorbed thiol against oxidation depends on the orientation of the organic molecules and the chemical state of the iron surface. High resolution XP-spectra of the S-2p-niveau are discussed and interpreted in comparison to results reported by Holm [3] and to own reference measurements. At oxide free surfaces the main signal results from the chemical interaction between metallic iron and the mercapto function, the binding energy for the S-2p-electrons being comparable to values obtained for FeS and segregated sulphur atoms by Panzner et al. [4]. On the preoxidized surface only oxidation products of the thiol could be detected as for example sulfonate ions (R-SO~) and species exhibiting an electron density at the sulphur atom similar to organic disulfides (R-S-S-R). Additionally performed electrochemical investigations lead to the following conclusions: The n-DMc film bound to the metal under cathodic potential control is extremly stable in an Ar-purged borate buffer (pH 8.5) at potentials between -1 .1 VSHE and +0.0 VsnE. In the corresponding cyclovoltammograms no signals of the clean iron could be observed. The application of more anodic potentials leads to the formation of one monolayer Fe3+-ions without any damage of the n-DNc layer. An oxidative desorption of the thiol molecules occurs only then, if the sample is polarized to -1 .1 VSnE in an O2-purged borate buffer for several minutes.

Surface characteristics of continuously annealed steel sheet in overaged condition

Abstract: The overaging treatment of a continuous annealing line was simulated in the laboratory. The chemical state of the surface of low carbon steel sheet was determined by using ESCA and SEM. The surfaces of a conventional, low alloyed deep drawing quality (DDQ) steel and a dual phase (DP) steel alloyed with Mn and Si were characterised in simulated and production line conditions. The influence of the surface state of the steels on the formation of surface phosphates was investigated. During overaging in the temperature range 200–400° C in a protective H2 + N2 atmosphere iron oxide is reduced to metallic iron. The alloying elements manganese and silicon are oxidised. Silicon especially is markedly enriched on the surface, in the form of pure Si02, due to its high diffusibility. The manganese and silicon oxides form particles on the surface during the overaging treatment. The results indicate that iron oxide is dissolved in the particles. Sodium and calcium are also present in their oxide states on the s...

The Role of Alloyed Molybdenum in the Dissolution and the Passivation of Nickel-Molybdenum Alloys in the Presence of Adsorbed Sulfur.

Abstract: The authors discuss the effects of Mo on the dissolution and the passivation of a Ni-2 atom percent (a/o) Mo(100) alloy in 0.05M H/sub 2/SO/sub 4/ investigated with or without adsorbed sulfur. Sulfur was preadsorbed on the alloy surface in H/sub 2/S-H/sub 2/ gas mixtures. Complete monolayers of S (i.e., 43 X 10/sup -9/ g/cm/sup 2/) were formed with pH/sub 2/ = 2 X 10/sup -4/ and T = 600{sup 0}C. The surface coverages by sulfur were measured using the sulfur 35 radioisotope (/sup 35/S) and the chemical state was analyzed by electron spectroscopy for chemical analysis. Potentiodynamic and potentiostatic measurements were performed, and the concentration of sulfur on the surface was measured as a function of the amount of dissolving molybdenum. The effect of S is found to be very weak compared to the one previously observed on Ni and Ni-Fe alloys, which shows that molybdenum counteracts the detrimental effects of adsorbed sulfur.

Auger electron spectroscopic studies of interfa ce and buried layer of soi structure formed by ion implantation

Abstract: The chemical composition and interface structure of silicon on insulator (SOI) formed by O+ (200 keV, 1.8×l018/cm-2) or N+ (190 keV, 1.8×1018/cm-2) implanted into silicon have been investigated by using Auger electron spectroscopy (AES) with in situ sputtering. For SOI structure produced by O+ implantation and annealing at 1300℃ for 5 hours, the characteristic Auger spectrum for the interface between the top silicon layer and the buried oxide layer was measured and a chemical state of silicon was identified, whose major transition was at 85 eV, different from that of the bulk silicon or silicon in SiO2. This chemical state was also discovered in the buried oxide layer. For SOI structure produced by N+ implantation and annealing at 1200℃ for 2 hours, a nitrogenrich porous layer was observed in the buried nitride layer. For both SOI structures, the strong asymmetry of the two main interfaces was observed. These results are in agreement with the results of infrared absorption (IR) analysis and transimission electron microscopy (TEM) analysis. The detailed explanation of these results is also presented in this paper.

Roles of Gas Phase and Surface Photolysis in Laser Chemical Vapor Deposition from Fe(CO)5

Abstract: The chemical state of the carbon and oxygen incorporated in iron films formed by laser photolysis of Fe(CO) 5 has been examined by profiling XPS analysis. A significant portion of the codeposited CO is photodissociated at the growing surface.

Measuring method for state correlation two-dimensional nuclear magnetic resonance

Abstract: PURPOSE:To enable separate measurement of anisotropy of a chemical shift of each nucleus even when a plurality of nucleuses of the same kind exist in a molecule by changing a physical or chemical state of a sample in a mixing period CONSTITUTION:Measurement of a sample of an object of measurement is divided into five periods A-E During a period from a preparatory period A to the end of a development period, the sample is put in a first physical or chemical state, eg a solid-phase state Then, in a mixing period C, the state of the sample is changed from the first state to a second state, eg a liquid-phase state, and thereafter this state is maintained until a detection period D is ended In this liquid state, an anisotropic mutual operation is averaged and information on NMR (nuclear magnetic resonance) of a plurality of nucleuses of the same kind can be obtained with excellent resolution and high sensitivity Accordingly, the NMR information on the sample in a solid state handed over in a free induction attenuation signal detected during the period D of the liquid state can be detected with high resolution and high sensitivity

Surface reaction mechanisms in the metallisation and etching of semiconductor materials.

Abstract: Surface spectroscopic techniques have been used to investigate aluminium deposition form tri-methyl aluminium (TMA) on Si(100), and the etching of InP by chlorine. Thermal reactions and processes stimulated by UV lamps and ion beams are examined. The results are interpreted in the light of the adsorption states which are formed and the surface transformations of chemical states which are observed to occur.