Showing papers on "Chemical state published in 1990"

Chemical reactions and physical property modifications induced by keV ion beams in polymers

Abstract: Factors influencing the chemical modification of polymers under ion bombardment are discussed. The chemical state and the electronic structure of ion-bombarded polymers are studied by XPS and REELS techniques. Ion bombardment of polymers is shown to induce well defined reactions involving the gradual modification of the original chemical structure within well defined fluence ranges, characteristic for each type of chemical reaction. The rate and the relative yield of the bombardment induced chemical reactions are shown to depend on the primary chemical structure of the bombarded polymers as well as on the total ion deposited energy, fluence and energy deposition mechanism. Such a dependence is discussed for some ion induced reactions in polyvynilpyridine (PVPY), polyethersulphone (PES). It is shown that polymer samples bombarded at very high fluence (10 15 −10 16 ions/cm 2 ) still keep “memory” of their primary stoichiometry and chemical structure showing spectroscopic characteristics similar to those of hydrogenated amorphous carbons. A number of cases are discussed in which the physical and electronic structure of the “carbonaceous” materials obtained depend upon the energy deposition mechanisms.

MoS 2 - x O x solid solutions in thin films produced by rf-sputter-deposition

Abstract: The chemical composition and structure of MoS2 solid lubricant films are intimately related to their friction and wear characteristics. We have conducted an x-ray photoelectron spectroscopy (XPS) study of 1-μm thick radio frequency (rf)-sputter-deposited MoS2 films to determine the chemical state of the films, focusing on the role of oxygen impurities. Concentrations of chemisorbed and bulk species were determined from the Mo 3d, S 2p, and O 1s peak shapes and intensities after annealing the films to temperatures from 425 to 975 K. Films deposited on substrates that were at ∼345 K [ambient temperature (AT) films] and on substrates heated to ∼525 K [high temperature (HT) films] both had ∼10% oxygen within the bulk of the films. The relative areas and shapes of the XPS peaks for the HT films at all annealing temperatures were consistent with the formation of a MoS2−xOx solid solution, where O atoms were probably substituted into S sites in the 2H–MoS2 crystal lattice. In AT films, this phase composition was stable only for annealing temperatures ≥725 K, in agreement with previous studies of the changes in crystal structure of AT films with annealing. The results are discussed in terms of previous studies of the structure and composition of sputter-deposited MoS2 films.

AES, EELS and XPS study of ion‐induced GaAs and InP(110) surface and subsurface modifications

Abstract: Low-energy Ar+-induced modifications of III–V semiconductor (110) surfaces have been investigated. XPS, angle-resolved AES and Auger profiles have been used to check the in-depth composition over the range of tens to hundreds of angstroms. The actual composition of the sputtered surfaces has been determined by either the elemental standard method or normalization to the cleaved surface signals. Auger and XPS lineshape analysis and EELS spectra provided information on the chemical state of the components in the sputter-altered region. GaAs and InP surfaces have been found to be metal enriched, the enrichment being larger at high ion beam energy. The 5 keV Ar+bombardment of the cleaved InP target results in the steady-state composition In(67)P(33) at the surface. The composition is graded in the subsurface region up to the stoichiometric value In(50)P(50). Although the sputter-altered GaAs region can be depicted roughly as As-depleted, the As concentration is larger at the surface than in the subsurface region. The surface ‘spike’ and the subsurface ‘dip’ in the As concentration strongly depend on the ion beam energy in terms of both the intensity and the extension in depth. These results indicate that As radiation-enhanced Gibbsian segregation and P preferential sputtering are the dominant mechanisms of surface modification in GaAs and InP, respectively.

Selective Chemical Etching of Latent Compositional Microstructures in Sputtered Co-Cr Films

Abstract: We examine the validity of a chemical etching method to reveal latent compositional microstructures in a sputtered Co-19.7 at% Cr film. Using dilute aqua regia as the etching solution, changes in the microstructure, composition and chemical state of Co and Cr through chemical etching are investigated. It is observed that the chemical etching progresses from the film surface towards the bottom, revealing an in-grain microstructure comprising periodic stripes (about 8-nm periodicity). The etching causes an increase in Cr and O content and the preferential formation of Cr oxide. These results suggest that the latent compositional microstructure is revealed by selective chemical etching due to the passivation of Cr-rich regions resulting in the preferential dissolution of Co-rich regions.

Spectroscopic Study of the Chemical State and Coloration of Chromium in Rutile

Abstract: The chemical states of Cr ions in rutile were studied using mainly electron spectroscopy for chemical analysis (ESCA), electron spin resonance (ESR), and diffuse reflectance spectroscopy. The study assumed that Cr3+ and Cr4+ which formed solid solutions with TiO2 possessed yellow and orange colors, respectively. A dark tinge accompanying the maple color of Cr-doped TiO2 probably was produced by undissolved CrO3−x (x∼ 0.5) occurring on the TiO2 grains. Incorporation of Sb into the Cr-doped TiO2 enhanced the solubility of Cr presumably because of the formation of Sb5+Cr3+ pairs and eventually decreased the dark tinge.

Method and apparatus for determining chemical states of living animal or human tissue using nuclear magnetic resonance

Abstract: In a method for determining chemical states of living animal or human tissue using nuclear magnetic resonance with a homogeneous constant magnetic field, the tissue is measured by means of a high-resolution nuclear magnetic resonance measurement and the measured values obtained are then evaluated by comparison with measured values from resonance measurements on comparable tissue to determine whether the chemical state of the tissue corresponds to a chemical normal state or to a deviating abnormal state. In order to enable a determination of chemical intermediate states to be made, it is proposed to compare the measured values obtained with such a series of reference measurements which also contain the detectable characteristic transition states between the chemical normal state and the abnormal end state and that the chemical transition state of the measured tissue sample is determined from the comparison.

Compositional and chemical modifications of V2O5 and NaVO3 induced by N2+ bombardment

Abstract: The chemical and compositional changes induced by 0.5–5 keV N2+ bombardment of V2O5 and NaVO3 have been studied by XPS. Both the atomic concentrations and the chemical states of the different constituents reach a steady state at an irradiation dose N 2 + cm 2 . As in Ar+ bombardment of these targets, the vanadium is reduced to lower oxidation states. The reactive nature of the N2+ species is however reflected by the opening of a chemical channel for oxygen removal (possibly by NOx formation) and retention of ~ 10–20% of the impinging nitrogen in the targets mainly as vanadium nitride, VN.

Characterization of nitrogen-ion-implanted aluminium

Abstract: Aluminium has been implanted with nitrogen ions at different temperatures. The implanted samples have been characterized by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). Deconvolution procedures are needed to separate the influence of the ion sputter profiling by AES and XPS from the nitrogen-ion-beam-induced effects. The chemical state of Al, N, O and C was identified by deconvolution of the measured spectra. In general, there were double-peak structures observed for N 1s and O 1s, identified as contributions from nitrides and weakly bound nitrogen, and oxides and weakly bound oxygen, respectively. Auger analysis confirms the influence of the nitrogen ion fluence on the shape of the concentration distribution. The influence of temperature on the chemical state of implanted aluminium and on the concentration distribution is discussed.

Chemical shifts in the MNN Auger spectra of Cd, In, Sn, Sb and Te

Abstract: The MNN Auger spectra of a series of elements, Cd through Te, have been examined as a function of chemical state. The spectra of Cd, In, Sn and Sb do not change shape significantly whether the element is present as a metal, semiconductor or insulator, e.g. Cd, CdTe or CdO. The Kinetic energies of the Auger electrons do shift by large, easily measurable, amounts of 3–6 eV. These shifts are to lower kinetic energy with respect to the pure metal and are largest for the oxides and least for the semiconductors. These spectra are atom-like and the two final-state holes are localized on one atom. The shape of the MNN Auger spectrum of Te reflects changes in its chemical state and shows shifts in energy similar to those seen for Cd, In, Sn and Sb. The changes in energy are much larger than those seen in photoemission and are the result of changes in the extra-atomic screening of the double-charged final-state ion.

A study of polar CdTe(111) surfaces using angle-resolved x-ray photoelectron and Auger electron spectroscopy and low-energy electron diffraction

Abstract: X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low‐energy electron diffraction (LEED) have been used to study the polar (111)Cd and (111)Te surfaces of intrinsic CdTe crystals. Complementary information on surface composition, chemical state of the surface elements, and surface structure was obtained. The Auger parameters were used to identify the chemical states of elements on surfaces of semi‐insulating undoped CdTe crystals which suffered from static charging effects. With this approach, we were able to determine that after chem‐mechanical polishing, the Te‐rich surface layer was mostly in the pure Te state. Only a trace amount of TeO2 was detectable. Sputtered and vacuum annealed (111) surfaces were found to be stoichiometric: both Cd and Te were in the chemical state of CdTe. Both (111) Cd and (111) Te surfaces showed sixfold symmetric LEED patterns. No evidence of surface reconstruction was found. Angle‐resolved XPS showed no significant difference between 0° and 70° ...

Composition and thickness of the surface layer on high Tc superconducting YBa2Cu3O7 − d thin films, studied by ARXPS☆

Abstract: With ARXPS, we investigated the surface layer on c-axis oriented high Tc superconducting YBa2Cu3O7 − d thin films. In the Y 3d feature, no chemical shift has been observed, indicating that Y is present in one chemical state only. In the Ba 3d and Ba 4d features, contributions of Ba components in two different chemical states have been found. We assign these two Ba lines to Ba in the superconducting YBa2Cu3O7−d material and to Ba in a non superconducting top layer. Also in the O 1s feature, two O lines have been discovered, one belonging to O in the YBa2Cu3O7−d and one belonging to O in the top layer. From the ARXPS measurements, indications have been found that in the surface layer 30 at. % O is missing. The ARXPS experiments show that the stable surface of c-axis oriented high Tc superconducting YBa2Cu3O7 − d thin films is the Ba-O plain, above the Y and that the superconducting film is covered with a non superconducting top layer with a typical thickness of 1.1 nm, containing Ba- and Cu-oxides and, due to transport through ambient, graphite, some carbonates and hydroxides.

Oxygen ion beam assisted thin film deposition

Abstract: Oxide films of several metals were deposited by ion beam sputtering and ion-assisted ion beam sputtering, and tested for chemical state data, impurity content and optical absorption. Results indicate that films are pure, adherent and non-porous. Preliminary data suggest that ion bombardment during film growth at the ion energies used in this study only aids in forming the correct stoichiometry and in lowering optical absorption for certain materials. Preliminary trends also seem to indicate that using metallic targets rather than oxide targets yields less optically absorbing films. X-ray photoelectron spectroscopy shows the formation of suboxides or oxycarbides for ion-assisted samples of Ta2O5.

Organics at surfaces, their detection and analysis by static secondary ion mass spectrometry

Abstract: The analysis of the surface chemistry of organic materials or of organic molecules at surfaces presents special problems. Firstly there is the requirement of high chemical specificity and the ability to detect small differences in chemical state. Secondly, organics are very sensitive to damage by the radiation used for the analysis. Over recent years, static secondary ion mass spectrometry (SSIMS) has been developed into a technique which is able to provide the power of mass spectrometry for the chemical characterization of surfaces. Furthermore, the advent of time-of-flight mass spectrometry techniques has enabled very high sensitivity with little sample damage. The power of the technique is illustrated by its application to four areas of surface investigation: the adsorption and reaction of propene at a ruthenium single crystal surface; the interaction of organic lubricants at a synthetic `gold' surface; the interaction of bioactive molecules at a model cell membrane surface, and the identification of contamination responsible for adhesive failure.

Surface studies of corrosion inhibitors in cooling water systems

Abstract: This paper reports electron spectroscopy for chemical analysis combined with argon-ion sputtering, used to obtain the thickness and composition profile of a mild steel tube from a dynamic simulation test (ie, pilot cooling tower) of a stabilized phosphate program The surface layer was found to be 3500 A thick, and contained carbon, phosphorus, calcium, iron, and oxygen The relative amounts and chemical state of the elements were found to vary with the thickness of the film The interface between the film and the mild steel tube was found to be predominantly FeOOH, with a small amount of FePO{sub 4}

A structure and chemical state of WO3-overlayer deposited on aerosil

Abstract: The work contains the results of UV-VIS and XPS study of WO3 phase deposited at the surface of aerosil by hydrolysis of WCl6. Results show that the overlayer is heterogeneous and consists of a very thin phase which contains interacting tungsten and silicon polyhedra as well as a phase of bulk WO3.

Chemical etching of InP

Abstract: The chemical etching of InP by iodic acid (HIO/sub 3/) solutions of varying weight percentage has been characterized in detail. The concentration dependence of etch rate of activation energies, and of etch profile has been evaluated. Solutions below 20 wt.% concentration are reaction-rate limited and are found to be useful for InP processing. The chemical state of the surface has been studied by X-ray photoelectron spectroscopy (XPS). These solutions oxidize the surface resulting in the formation of InPO/sub 4/:xH/sub 2/O, which could be useful for Schottky and MIS device applications. The use of a 20 wt.% solution for mesa type etching applications and a 5-10 wt.% solution for cleaning purposes is suggested. >

Chapter 1 Surface Spectroscopic Techniques

Abstract: Publisher Summary This chapter discusses the surface spectroscopic techniques. Surface analysis of heterogeneous catalysts involves the measurement of three different quantities. The most important of these are the qualitative identification of surface species—that is, what atom-type is at the surface. The second concerns the chemical state of these atoms—that is, the oxidation state of surface species. It is necessary to determine the spatial location of the surface structures. Most of the surface spectroscopies require an ordered surface—that is, a single crystal. The electron spectroscopies fall in this category, although Auger spectroscopy is not so rectricted, and has been successfully applied to the study of promoter distribution in a commercial ammonia synthesis K2O-Al2O3-Fe catalyst. The small area samples, single crystal or polycrystal-line foils, but well suited to characterize surfaces in ultrahigh vacuum by low energy electron diffraction (LEED), Auger spectroscopy (AES) or other surface sensitive techniques, can be used as model catalysts, as a special configuration provides parallel kinetic studies under conditions that are virtually identical to those used in the chemical technology.

Process and device for detecting chemical states of living animal or human tissues by magnetic resonance

Abstract: A process is disclosed for detecting chemical states of living animal or human tissues by magnetic resonance by means of a homogeneous constant magnetic field. The tissue is measured according to a high resolution magnetic resonance process and the measurement values obtained are evaluated by comparison with resonance measurement values of comparable tissues, in order to determine whether the chemical state of the tissue corresponds to a normal chemical state or to an abnormal state that deviates from the norm. In order to allow intermediary chemical states to be detected as well, the measurement values are compared with a series of reference measurements that include detectable characteristic transition states between the normal chemical state and the final abnormal state. The chemical transition state of the measured tissued sample is determined by comparison.