Application Of X-ray Photoelectron Spectroscopy Research Articles

Effect of heat treatments on electric dipole at metal/high- k dielectric interfaces measured by in situ XPS

The paper describes the application of X-ray photoelectron spectroscopy (XPS) based method to quantify changes in the electric dipole formed at the metal/dielectric interface following heat treatments of metal–oxide–semiconductor (MOS) stack in different environments. The presented results on Me (Me = Au, Ni)/dielectric (dielectric = HfO 2, LaAlO 3) evidence the oxygen vacancies generated in dielectric contribute to the effective work function changes.

Quasi in situ XPS investigations on intercalation mechanisms in Li-ion battery materials

New concepts for Li-ion batteries are of growing interest for high-performance applications. One aim is the search for new electrode materials with superior properties and their detailed characterization. We demonstrate the application of X-ray photoelectron spectroscopy (XPS) to investigate electrode materials (LiCoO(2), LiCrMnO(4)) during electrochemical cycling. The optimization of a "quasi in situ" analysis, by transferring the samples with a transport chamber from the glove box to the XPS chamber, and the reliability of the experiments performed are shown. The behavior of characteristic chemical species at the electrodes and the changes in oxidation states of LiCrMnO(4) during cycling is discussed. The formation of Cr(6+) is suspected as a possible reason for irreversible capacity loss during charging up to complete Li deintercalation (approximately 5.2 V).

Selected Area XPS Analysis for Identification of Pigment Compounds in Microscopic Paint Flakes

The application of X-ray photoelectron spectroscopy to the analysis of paint flakes from a painting by Henry Fuseli (1741–1825) is presented. Historically, the application of XPS to art conservation and restoration studies has been limited by the poor spatial resolution of the technique. Presented here is the successful analysis of paint flakes in the order of 100 μm using “imaging” XPS in conjunction with selected area analysis. Raman microscopy failed to satisfactorily identify the compounds present in this instance, and energy dispersive spectroscopy could not differentiate between lead and sulphur (two of the elements of interest) due to the limited energy resolution inherent in that technique. Using XPS analysis of the lead 4f peak revealed that the pigment was a lead-based pigment, in this case comprising exclusively lead-sulphur compounds.

PH-Induced Protonation of Lysine in Aqueous Solution Causes Chemical Shifts in X-ray Photoelectron Spectroscopy

We demonstrate the applicability of X-ray photoelectron spectroscopy to obtain charge- and site-specific electronic structural information of biomolecules in aqueous solution. Changing the pH of an aqueous solution of lysine from basic to acidic results in nitrogen 1s and carbon 1s chemical shifts to higher binding energies. These shifts are associated with the sequential protonation of the two amino groups, which affects both charge state and hydrogen bonding to the surrounding water molecules. The N1s chemical shift is 2.2 eV, and for carbon atoms directly neighboring a nitrogen the shift for C1s is approximately 0.4 eV. The experimental binding energies agree reasonably with our calculated energies of lysine(aq) for different pH values.

XPS at Solid—Aqueous Solution Interface

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Zinc treatment effects on corrosion behavior of Alloy 600 in high temperature, hydrogenated water

Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 °C were found to reduce the corrosion rate of Alloy 600 (UNS N06600) by about 40% relative to a non-zinc baseline test [S.E. Ziemniak, M. Hanson, Corros. Sci., in press, doi:10.1016/j.corsci.2005.01.006]. Characterizations of the corrosion oxide layer via SEM/TEM and grazing incidence X-ray diffraction confirmed the presence of a chromite-rich oxide phase and recrystallized nickel. The oxide crystals had an approximate surface density of 3500 μm −2 and an average size of 11 ± 5 nm. Application of X-ray photoelectron spectroscopy with argon ion milling, followed by target factor analyses, permitted speciated composition versus depth profiles to be obtained. Numerical integration of the profiles revealed that: (1) alloy oxidation occurred non-selectively and (2) zinc(II) ions were incorporated into the chromite-rich spinel: (Zn 0.55Ni 0.3Fe 0.15)(Fe 0.25Cr 0.75) 2O 4. Spinel stoichiometry places the trivalent ion composition in the single phase oxide region, consistent with the absence of the usual outer, ferrite-rich solvus layer. By comparison with compositions of the chromite-rich spinel obtained in the non-zinc baseline test, it is hypothesized that zinc(II) ion incorporation was controlled by the equilibrium for 0.55 Zn 2 + ( aq ) + ( Ni 0.7 Fe 0.3 ) ( Fe 0.3 Cr 0.7 ) 2 O 4 ( s ) ⇄ 0.40 Ni 2 + ( aq ) + 0.15 Fe 2 + ( aq ) + ( Zn 0.55 Ni 0.3 Fe 0.15 ) ( Fe 0.3 Cr 0.7 ) 2 O 4 ( s ) It is estimated that only 8% of the Ni(II) ions generated during non-selective oxidation of the alloy were retained as Ni(II) in the corrosion layer; the remainder either recrystallized to Ni(0) (38%) or were released to the aqueous phase (54%).

Electron effective attenuation lengths in electron spectroscopies

An important measure of the opacity of a solid with respect to monoenergetic electrons in a solid is the effective attenuation length (EAL). However, there is much controversy in the literature concerning the definition of this parameter. It has been shown recently that different quantitative applications of electron spectroscopies require EALs resulting from different expressions. In the present report, these expressions for typical applications of X-ray photoelectron spectroscopy and Auger electron spectroscopy are briefly reviewed. The EALs needed for determination of overlayer thicknesses and for measurement of surface composition are compared for the same experimental configuration. These comparisons are made for selected photoelectron lines for which we expect strong electron elastic-scattering effects (Cu2s and Cu2p 3/2 in Cu and Au4s and Au4f 7/2 in Au). Substantial differences between EALs for these lines were found for the two applications. Synchrotron radiation can be used for experimental determination of the EAL values. These values can facilitate evaluation of the reliability of theoretical models used in calculations of EALs.

Spectromicroscopic study of bimetal/semiconductor interfaces by synchrotron light

Third generation synchrotron light sources like Elettra offer the opportunity to focus a high-intensity X-ray photon beam to the submicron region. This allows applications of X-ray photoelectron spectroscopy to determine the composition, chemical bonding and electronic structure at the microscopic level with a lateral resolution of about 100 nm. In this way phenomena on heterogeneous surfaces and interfaces can be studied, and among them metal/semiconductor interfaces are of particular interest. Synchrotron radiation scanning photoemission microscopy was used to investigate ultra-thin films of Au, Ag and Ni on a Si(1 1 1) surface to reveal the fundamental processes in bimetal/semiconductor interface formation. The local interactions of the thin confined Au and Ni metal films with an Ag/Si(1 1 1) interface covered with three-dimensional micron-sized islands was studied as a function of annealing temperature. From the photoelectron spectra and spatially resolved two-dimensional maps we followed the formation of new phases and their stability.

Chemical analysis of plasma-polymerized films: The application of X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (NEXAFS) and fourier transform infrared spectroscopy (FTIR)

Selected FTIR, XPS and NEXAFS spectroscopy results obtained with films deposited with different plasma polymerization processes and different monomers (styrene, acetylene, ethylene and butadiene) are presented. In detail FTIR spectra, XPS surveys, XPS valence bands and core level signals including shake-up features as well as carbon K-edge absorption spectra are qualitatively and, in some cases, semi-quantitatively considered. Information on the film formation, the chemistry of the films and the film stability against air exposure are derived from spectroscopic features. With styrene chemically rather well defined plasma polymer layers can be formed with rather high deposition rates applying a pulse plasma process. Using ethylene, acetylene or butadiene as a monomer in the plasma deposition process the deposition rates are smaller. Using these monomers plasma polymer films can be obtained with a primary chemical structure which is similar to each other but more or less different from those of the respective conventional polymers. The main difference between these samples is their individual concentration of unsaturated carbon species. Finally, a technologically relevant example, i.e. a plasma deposited polymer barrier layer deposited on the inner wall of a poly(ethylene) vessel is briefly considered.

X-ray photoelectron spectroscopy as a tool for studies of the surface layer of microspheres. The case of polystyrene and poly(styrene-acrolein) microspheres with attached human serum albumin

The application of X-ray photoelectron spectroscopy (XPS) for studies of surface layers of objects with spherical shape was investigated using as examples polystyrene and poly(styrene–acrolein) microspheres with attached human serum albumin (HSA). The amounts of immobilized protein were determined by the standard biochemical Lowry method and by XPS, using the intensity of the N1s signals of HSA as a basis for evaluation. The XPS data were treated by taking into account the spherical shape of the particles analyzed (variable take-off angle of ejected electrons). The best agreement between the results of the biochemical and XPS determinations was found assuming that for the average particle the takeoff angle varies from 0° to 72.7°. This reflects the fact that in the multilayer arrangement of particles, placed onto the support of the XPS apparatus, the particles from the upper layer partially screen the edges of the particles in the layer below.

Strategies towards functionalised electronically conducting organic copolymers: Part 2. Copolymerisation

Here we discuss the application of X-ray photoelectron spectroscopy and absorbance–reflectance FT-IR spectroscopy to establish and quantify reactivity relationships between a range of thiophene and pyrrole monomers. In particular we investigate the application of these techniques to the characterisation of conducting polymer materials grown potentiostatically from solutions containing a binary mixture of monomers. Our data have shown that XPS is especially effective in determining polymer composition and the linear correlation between this and solution composition has enabled prescriptive synthesis of copolymer materials from the different combinations of monomers described here. This technique is much more convenient and more reliable than elemental analysis. In contrast we show that FT-IR studies, whilst providing a useful qualitative guide to the functional group content of the material, do not facilitate detailed quantitative analysis because of large intrinsic errors.

Determination of the inelastic mean free path of electrons in polyaniline samples by elastic peak electron spectroscopy

Application of x-ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy for quantitative characterisation of surfaces requires knowledge of the electron inelastic mean free path and its energy dependence. Inelastic mean free path values have been determined for a wide variety of solids using theoretical and experimental methods. However, the number of published inelastic mean free path values for polymers is limited. In principle, these values for polymers can be estimated using predictive formulae such as TPP-2M and the G1 formula of Gries. An alternative method for inelastic mean free path determination in polymers is elastic peak electron spectroscopy. In the present work, the surface chemical composition of polyaniline samples (undoped and doped with palladium) was analysed quantitatively using x-ray photoelectron spectroscopy. The inelastic mean free path values were determined by elastic peak electron spectroscopy using a high-energy-resolution hemispherical analyser in the energy range 500– 5000 eV. The resulting inelastic mean free path values evaluated using Ni and Ag standards are smaller than the values resulting from the G1 predictive formula of Gries and the TPP-2M predictive formula of Tanuma et al. The discrepancies in the inelastic mean free path values are discussed extensively. Copyright © 2000 John Wiley & Sons, Ltd.

APPLICATIONS OF X-RAY PHOTOELECTRON SPECTROSCOPY AND STATIC SECONDARY ION MASS SPECTROMETRY IN SURFACE CHARACTERIZATION OF COPOLYMERS AND POLYMERS BLENDS

Article APPLICATIONS OF X-RAY PHOTOELECTRON SPECTROSCOPY AND STATIC SECONDARY ION MASS SPECTROMETRY IN SURFACE CHARACTERIZATION OF COPOLYMERS AND POLYMERS BLENDS was published on December 1, 2000 in the journal Reviews in Chemical Engineering (volume 16, issue 4).

99/03518 A survey of the application of X-ray photoelectron spectroscopy to flotation research: Buckley, A. N. Colloids Surf., A, 1994, 93, 159–172

99/03518 A survey of the application of X-ray photoelectron spectroscopy to flotation research: Buckley, A. N. Colloids Surf., A, 1994, 93, 159–172

Thin film deposition by reactive magnetron sputtering: On the influence of target oxidation and its effect on surface properties

The application of X-ray photoelectron spectroscopy (XPS) for the characterization of deposited thin indium tin oxide (ITO) layers by reactive direct-current magnetron sputtering in Ar:O 2 gas mixtures is performed. The influence of the gas mixture and the sputter-process duration on the discharge power and oxidation state of the target implies that the target state is an essential parameter for the production of ITO films. For understanding the plasma-surface interaction, the plasma has been monitored in front of the target and near the substrate by means of Langmuir-probe diagnostics. The internal plasma parameters, namely n e and k b T e, at the target also at the substrate have been determined as functions of discharge power and radial position. XPS analyses indicate a “selective oxidation” of tin compared to indium as well as a change of the surface composition during the sputter process.

ISS Assessment of the Influence of Nonpore Surface in the XPS Analysis of Oil-Producing Reservoir Rocks

The application of X-ray photoelectron spectroscopy (XPS) to oil-producing reservoir rocks is new and has shown that pore surface concentrations can be related to rock wettability. In the preparation of fresh fractures of rocks, however, some nonpore surface corresponding to the connection regions in the rocks is created and exposed to XPS. To assess the potential influence of this nonpore surface in the XPS analysis of rocks here we use ion scattering spectroscopy (ISS), which has a resolution comparable to the size of the pores, higher than that of XPS, with an ion gun of He+at maximum focus. Sample charging effects are partially eliminated with a flood gun of low energy electrons. All the ISS signals are identified by means of a formula which corrects any residual charging on the samples. Three rock samples are analyzed by XPS and ISS. The almost unchanged ISS spectra obtained at different points of a given sample suggest that the nonpore surface created in the fracture process is negligibly small, indicating that XPS data, from a larger surface spot, represents the composition of true pore surfaces. The significant changes observed in ISS spectra from different samples indicate that ISS is sample specific.

Application of X-ray photoelectron spectroscopy to the study of degradation mechanisms of epoxy-bonded joints of zinc coated steel

The degradation mechanisms of bonded joints made from an electroplated-phosphated steel (EZ2) or a hot-dipped galvanized steel (G2F), and a hot-curing epoxy adhesive (1K-A) were investigated using X-ray photoelectron spectroscopy. In a first stage, the cured adhesive, the metal substrates, and the interfacial adhesive and metal sides of the fracture surfaces of unaged bonded joints were analyzed to establish the locus of failure: Adhesive for EZ2/1K-A, and cohesive for G2F/1K-A. The bonded joints were then aged following two accelerated ageing tests: The ‘cataplasme humide’ and the ‘water immersion’ tests. The Zn2p 3/2 and O 1s high resolution spectrum, as well as the ZnL 3M 45M 45 Auger peaks enabled to determine the corrosion products formed in the various zones of the fracture surfaces. The ingress of water was responsible for the total dissolution of the phosphate coating near the edges of the bonded joints for EZ2 whereas intergranular corrosion phenomena occurred on the whole metal interfacial side of G2F/1K-A bonded joints.

Surface chemical analysis in coal preparation research: complementary information from XPS and ToF-SIMS

The application of X-ray photoelectron spectroscopy (XPS) to coal surface characterisation for preparation research is described. Progress towards the acquisition of complementary surface chemical information by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is also discussed. Surface-based beneficiation techniques such as flotation are assuming greater importance as the proportion of fines in raw coal increases due to the proliferation of high capacity mining methods. A necessary condition for the floatability of a coal particle is adequate hydrophobicity, and the degree of hydrophobicity of the flotation concentrate is one factor influencing the ease with which its dewatering can be affected. The hydrophobicity of a coal is very difficult to measure directly because of microporosity, and it is often necessary to deduce the degree of hydrophobicity from a knowledge of the surface chemistry. XPS is able to provide sufficient analytical data to allow relative levels of hydrophobicity to be estimated. In principle, ToF-SIMS should be able to supply additional information enabling refinement of such estimates; however, there are insufficient data at present to allow the ionic fragments detected to be related to specific functional groups at the coal surface.

A survey of the application of X-ray photoelectron spectroscopy to flotation research

The application of X-ray photoelectron spectorscopy (XPS) to research into the beneficiation of minerals and coal by flotation is considered in general terms. The practical aspects of preparing the maintaining specimens for XPS that provide meaningful information are discussed in some detail. Examples of recent XPS work on sulfide mineral/collector systems and coal surface characterization are described.

Aging Process of Metal/Epoxy Laminates Investigated with X-ray Photoelectron Microscopy and Spectroscopy

Abstract In this article we describe the application of X-ray photoelectron spectroscopy to epoxy/dicyandiamide laminates on zinc galvanized steel which were aged under different environmental conditions involving high humidity and temperatures. X-ray photoelectron microscopy allows us to identify the distribution of chemical elements with a lateral resolution of 10μm. Areas selected in the microscopy mode were then analyzed in the spectroscopy mode in order to get information on the local chemical composition. We compared the spectroscopic features of the aged but freshly delaminated surfaces of samples stored under ambient conditions at room temperature with samples exposed to the “Kataplasmann” and the “KWT” test, respectively. Furthermore, a comparison was made with a model sample which was prepared in vacuum and on which the curing process was investigated. Though there is no substantial loss in the lap-shear strength of the samples, we find drastic spectroscopic changes in the Kataplasma and KWT tre...