Quantitative Spectrum Analysis Research Articles

Quantitative analysis of multi-element oxide thin films by angle-resolved XPS: Application to ultra-thin oxide films on MgAl substrates

An original procedure has been developed for the quantitative analysis and microstructural interpretation of angle-resolved X-ray photoelectron spectra (AR-XPS) of very thin (<6nm), multi-element oxide films as grown on metallic binary alloy substrates by, e.g., thermal or plasma oxidation. To this end, first an approach has been given to retrieve the different metallic, oxidic and oxygen primary zero-loss (PZL) intensities from the measured AR-XPS spectra of the bare and oxidized alloy. The principal equations for the determination of the oxide-film thickness, composition and constitution from the resolved PZL intensities have been presented. On this basis, various corresponding calculation routes have been distinguished. The procedure has been applied to the case of very thin (<6nm), mixed (Mg, Al)-oxide films on bare Mg-based MgAl substrates as grown by dry, thermal oxidation at room temperature. The results obtained on the thickness, composition, defect structure and constitution of the oxide-film have been discussed as function of the bulk Al alloying content and the applied partial pressure of oxygen.

Transmission electron microscopy and energy dispersive X-ray spectroscopy on the worn surface of nano-structured TiAlN/VN multilayer coating

Nano-structured TiAlN/VN multilayer hard coatings grown by cathodic arc metal ion etching and unbalanced magnetron sputtering deposition have repeatedly shown low coefficients of friction and wear. In this paper, we employed the combined methods of cross-sectional ion beam milling sample preparation, conventional transmission electron microscopy, energy dispersive X-ray spectroscopy and quantitative spectrum analysis to give a comprehensive characterization of wear induced tribofilm, worn TiAlN/VN surface as well as wear debris. The major wear mechanism operating in the TiAlN/VN coating is the tribo-oxidation wear. A 20–50 nm thick tribofilm was observed on the TiAlN/VN worn surface, having inhomogeneous density, amorphous structure and multicomponent V–Al–Ti–O composition. Therefore the real sliding contact during the ball-on-disk test was a three-body sliding system including the tribofilm, in which the self-sintering and shearing deformation of the multicomponent oxide film played a significant role in determining the low friction coefficient. Owing to the low friction and high hardness, the TiAlN/VN worn surface retained good structural integrity without any crack, delamination or detectable deformation, resulting in minimized mechanical wear.

Direct extraction of Raman line-shapes from congested CARS spectra

We show that Raman line-shapes can be extracted directly from congested coherent anti-Stokes Raman scattering (CARS) spectra, by using a numerical method to retrieve the phase-information hidden in measured CARS spectra. The proposed method utilizes the maximum entropy (ME) model to fit the CARS spectra and to further extract the imaginary part of the Raman susceptibility providing the Raman line-shape similar to the spontaneous Raman scattering spectrum. It circumvents the challenges arising with experimentally determining the real and imaginary parts of the susceptibility independently. Another important advantage of this method is that no a priori information regarding the vibrational resonances is required in the analysis. This permits, for the first time, the quantitative analysis of CARS spectra and microscopy images without any knowledge of e.g. sample composition or Raman response.

Electron Paramagnetic Resonance Spectroscopy Studies of Oxidative Degradation of an Active Pharmaceutical Ingredient and Quantitative Analysis of the Organic Radical Intermediates Using Partial Least-Squares Regression

Electron paramagnetic resonance (EPR) spectroscopy was used to study the radical species formed during the oxidation of an active pharmaceutical ingredient in the solid state. It was found that the extent of radical generation correlated to the formation of an oxidative degradation product. Multifrequency EPR and electron nuclear double resonance spectroscopy gave additional information on the identity of the organic radical species involved in the oxidation process, and a mechanism was proposed for the degradation, involving the formation of both carbon-centered and peroxy radicals. The multivariate analysis technique of partial least-squares (PLS) regression was then used to determine the extent of oxidation of the active pharmaceutical ingredient from the EPR spectra. The suitability of this approach was demonstrated from its application to a series of standards. The conventional approach for the quantitative analysis of EPR spectra is to measure the peak height or to perform double integration of the spectral region containing the signal of interest. Both of these methods have intrinsic errors associated with them, particularly for weak EPR signals with a poor signal-to-noise ratio or a sloping background response. The results obtained showed that greatly improved quantitation was obtained using the PLS regression approach.

US 708 – an unbound hyper-velocity subluminous O star

We report the discovery of an unbound hyper-velocity star, US 708, in the Milky Way halo, with a heliocentric radial velocity of +708 ± 15 km s -1 . A quantitative NLTE model atmosphere analysis of optical spectra obtained with LRIS at the Keck I telescope shows that US 708 is an extremely helium-rich (N He /N H = 10) subluminous O type star with T eff = 44 500 K, logy = 5.23 at a distance of 19 kpc. Its Galactic rest frame velocity is at least 751 km s -1 , much higher than the local Galactic escape velocity indicating that the star is unbound to the Galaxy. It has been suggested that such hyper-velocity stars can be formed by the tidal disruption of a binary through interaction with the super-massive black hole (SMBH) at the Galactic centre (GC). Numerical kinemalical experiments are carried out to reconstruct the path from the GC. US 708 needs about 32 Myrs to travel from the GC to its present position, less than its evolutionary lifetime. Its predicted proper motion μ α cos δ = -2.3 mas yr -1 and μ δ = -2.4 mas yr -1 should be measurable by future space missions. We conjecture that US 708 is formed by the merger of two helium white dwarfs in a close binary induced by the interaction with the SMBH in the GC and then escaped.

HE 0437-5439: An Unbound Hypervelocity Main-Sequence B-Type Star

We report the discovery of a 16th magnitude star, HE 0437-5439, with a heliocentric radial velocity of +723 ± 3 km s-1. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and UVES shows that HE 0437-5439 is a main-sequence B-type star with Teff = 20,350 K, log g = 3.77, a solar (within a factor of a few) helium abundance and metal content, and rotating at v sin i = 54 km s-1. Using appropriate evolutionary tracks, we derive a mass of 8 M☉ and a corresponding distance of 61 kpc. Its Galactic rest-frame velocity is at least 563 km s-1, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hypervelocity stars can be formed by the tidal disruption of a binary through interaction with the supermassive black hole at the Galactic center (GC). HE 0437-5439 needs about 100 Myr to travel from the GC to its present position, much longer than its main-sequence lifetime of 25 Myr. This can only be reconciled if HE 0437-5439 is a blue straggler star. In this case, the predicted proper motion is so small that it can only be measured by future space missions. Since the star is much closer to the Large Magellanic Cloud (LMC; 18 kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2 mas yr-1 (relative to the LMC), large enough to be measurable with conventional techniques from the ground. The LMC origin could also be tested by a high-precision abundance analysis.

Quantitative analysis ofSr2RuO4angle-resolved photoemission spectra: Many-body interactions in a model Fermi liquid

Angle-resolved photoemission spectroscopy (ARPES) spectra hold a wealth of information about the many-body interactions in a correlated material. However, the quantitative analysis of ARPES spectra to extract the various coupling parameters in a consistent manner is extremely challenging, even for a model Fermi liquid system. We propose a fitting procedure which allows quantitative access to the intrinsic line shape, deconvolved of energy and momentum resolution effects, of the correlated two-dimensional material ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. In correlated two-dimensional materials, we find an ARPES linewidth that is narrower than its binding energy, a key property of quasiparticles within Fermi liquid theory. We also find that when the electron-electron scattering component is separated from the electron-phonon and impurity scattering terms, it decreases with a functional form compatible with Fermi liquid theory as the Fermi energy is approached. In combination with the previously determined Fermi surface, these results give a complete picture of a Fermi liquid system via ARPES. Furthermore, we show that the magnitude of the extracted imaginary part of the self-energy is in remarkable agreement with DC transport measurements.

Quantitative analysis of directional spontaneous emission spectra from light sources in photonic crystals

We have performed angle-resolved measurements of spontaneous-emission spectra from laser dyes and quantum dots in opal and inverse opal photonic crystals. Pronounced directional dependencies of the emission spectra are observed: angular ranges of strongly reduced emission adjoin with angular ranges of enhanced emission. It appears that emission from embedded light sources is affected both by the periodicity and by the structural imperfections of the crystals: the photons are Bragg diffracted by lattice planes and scattered by unavoidable structural disorder. Using a model comprising diffuse light transport and photonic band structure, we quantitatively explain the directional emission spectra. This work provides detailed understanding of the transport of spontaneously emitted light in real photonic crystals, which is essential in the interpretation of quantum optics in photonic-band-gap crystals and for applications wherein directional emission and total emission power are controlled.

Truly Quantitative XPS Characterization of Organic Monolayers on Silicon: Study of Alkyl and Alkoxy Monolayers on H−Si(111)

The quantitative characterization of the chemical composition (bonding at grafted and ungrafted sites, surface coverage) is a key issue for the application of silicon-organic monolayer hybrid interfaces. The primary purpose of this article is to demonstrate that X-ray photoelectron spectroscopy (XPS) requires to be truly quantitative to deal with two main questions. The first one is accounting for X-ray photodiffraction (XPD), a well-known phenomenon that is responsible for azimuthal variations of the XPS signal intensity. A simple procedure is proposed to account for XPD in angle-resolved measurements. The second critical point concerns the choice of photoelectron attenuation lengths (AL). This article demonstrates that n-alkanethiol self-assembled monolayers on Au(111) can be used as a reference system to derive the effective monolayer thickness on silicon substrates and that one may use the empirical relationship established by Laibinis and co-workers to calculate the relevant ALs (Laibinis, P. E.; Bain, C. D.; Whitesides, G. M. J. Phys. Chem. 1991, 95, 7017). A self-consistent approach is presented to justify the above assertions and to give a complete compositional description of alkyl and alkoxy monolayers directly grafted on atomically flat H-Si(111) surfaces. Direct evidences are provided that a Si-C and a Si-O-C linkage is formed, respectively, after reaction with decene and decanol and that the ungrafted sites remain saturated with H atoms. Moreover, the quantitative spectra analysis of satellite peaks at fixed polar angle and three independent angle-resolved Si2p and C1s spectra all give the same surface coverage very close to its theoretical limit.

On the energy dissipation process in incoherent electron scattering

The energy dissipation process in non-crystalline solids for electron beam techniques is reviewed. The characteristics for the interaction of the probe electron with the electronic as well as the ionic subsystem of a solid are discussed, corresponding to inelastic and elastic scattering, respectively. Since the energy dissipation process is responsible for the energy and angular spectrum of techniques such as transmission electron microscopy (TEM), electron probe microanalysis (EPMA), (reflection) electron energy loss spectroscopy ((R)EELS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), and the like, quantitative spectrum interpretation requires a sound theoretical description of multiple scattering processes. The theory of non-coherent multiple scattering is outlined using a Boltzmann-type kinetic equation as a starting point. The only assumption made is that the elastic interaction can be represented by a static spherically symmetric potential. This leads to a simple and general expression for the generalized loss function describing the energy losses and deflections experienced by a particle as a function of the pathlength travelled in the solid. The loss function is found to be governed by the collision statistics, on the one hand and the fluctuations of the energy loss and deflection angle, on the other hand and in this way provides a sound basis for rigorous quantitative spectrum analysis. Decomposition of experimental spectra is straightforward if different types of inelastic scattering are uncorrelated, a requirement that is fulfilled if only one of the considered processes takes place in a region in space whose dimension exceeds the elastic mean free path. Spectrum analysis procedures on this basis are discussed for selected techniques including EELS in the TEM, reflection EELS, X-ray production in EPMA and decomposition of photoelectron spectra in XPS.

Raman scattering coefficients of symmetrical stretching modes of microstructural units in sodium silicate melts

Quantitative analysis of Raman spectra of vitreous or molten silicate is always one of the key subjects in some fields, e.g. materials science, geological physi cs, etc. But there are many difficulties with this analysis, one of which is the determination of Raman scattering coefficient. Not long ago, we developed a new method for the calculation of Raman spectrum of amorphous silicate. Essentiall y, this method combines the molecular dynamics simulation with wilson's GF matri x method, electro_optical parameter method and bond polarizability model. With t his theoretical method, we have studied the Raman scattering coefficients of sym metrical stretching modes of Qi in sodium silicate melts, and concluded th at these coefficients are independent of composition. Meanwhile, the five values of the coefficients are also given as follows: S0=１, S1=0514, S2=0 242, S3=0090 and S4=0015 In order to apply these quantities to experiments, the Raman spectrum of sodium disilicate melt has been measured and its high_frequency envelope has been deconvolved into three Gaussian bands. Fina lly, the molar fractions of Qi were achieved by dividing the area fraction s of the three Gaussian bands by corresponding scattering coefficients. Addition ally, combining the results of theoretical calculation and quantitative analysis of experimental spectra, we found that the intensities of anti_symmetrical stre tching modes of Q0 and Q2 in sodium silicate melts are so strong tha t they cannot be neglected in the deconvolution process.

Quantitative oscillator analysis of IR-optical spectra on spin-cast chitosan films

Infrared optical properties of spin-cast chitosan films have been determined using spectroscopic ellipsometry. Infrared index of refraction and extinction coefficients from 750 cm–1to 4000 cm–1were determined using ellipsometric data fits to dispersion models based on Gaussian shaped oscillators. The free electron contribution was analyzed using a Drude model. This modeling determined that optical anisotropy was present over the entire infrared region. Line shape and oscillator strength analysis was performed to determine oscillator strengths, abundance, and relative bond strength.

Quantitative analysis of XANES spectra of disordered systems based on molecular dynamics

A general procedure which computes X-ray absorption near-edge structure (XANES) spectra starting from the individual configurations obtained from molecular dynamics (MD) simulations has been developed. This method allows one to perform a quantitative analysis of the XANES spectra of disordered systems and to estimate the effect of disorder on the low-energy region of the X-ray absorption spectra. As a test case, a Ni2+ aqueous solution has been investigated. The configurational averaged XANES theoretical spectrum obtained from the MD configurations compares well with the experimental data. This confirms simultaneously the reliability of the procedure and of the structural results obtained from the MD simulation.

Automated evaluation of chemical shift perturbation spectra: New approaches to quantitative analysis of receptor-ligand interaction NMR spectra.

This paper presents new methods designed for quantitative analysis of chemical shift perturbation NMR spectra. The methods automatically trace the displacements of cross peaks between a perturbed test spectrum and the reference spectrum (or among a series of titration spectra), and measure the changes of chemical shifts, heights, and widths of the altered peaks. The methods are primary aimed at the (1)H-(15)N HSQC spectra of relatively small proteins (<15 kDa) assuming fast exchange between free and ligand-bound states on the chemical shift time scale, or for comparing spectra of free and fully bound states in the slow exchange situation. Using the (1)H-(15)N HSQC spectra from a titration experiment of the 74-residue Pex13p SH3 domain with a Pex14p peptide ligand (14 residues, K (d)= approximately 40 microM), we demonstrate the scope and limits of our automatic peak tracing (APET) algorithm for efficient scoring of high-throughput SAR by NMR type HSQC spectra, and progressive peak tracing (PROPET) algorithm for detailed analysis of ligand titration spectra. Simulated spectra with low signal-to-noise ratios (S/N ranged from 20 to 1) were used to demonstrate the reliability and reproducibility of the results when dealing with poor quality spectra. These algorithms have been implemented in a new software module, FELIX-Autoscreen, for streamlined processing, analysis and visualization of SAR by NMR and other high-throughput receptor/ligand interaction experiments.

QUEELS software package for calculation of surface effects in electron spectra

AbstractSurface analysis based on the interpretation of electron spectroscopy such as x‐ray photoelectron spectroscopy, Auger electron spectroscopy, or reflection electron energy loss spectroscopy are influenced by the inelastic scattering processes that take place when an electron moves in the region near a solid surface. The actual energy losses depend on the particular experimental situation. Thus, an electron is attracted by its image charge when it is moving in the vacuum. It will therefore lose energy even after it has left the surface and, similarly, an electron that moves in the vacuum towards the solid surface gains energy. Likewise, the scattering properties for an electron moving close to the surface are different from those of an electron moving in the bulk of the solid. In photoemission and Auger experiments the effect of the static hole will also affect the scattering probabilities of the electron in the first few ångströms as it moves away from the point of excitation. These effects will also cause the ‘effective’ inelastic mean free path to depend on the position of the electron with respect to the surface and with respect to the point of excitation. In the past years, we have developed models to describe these effects within a dielectric response theory for different cases of electrons moving near surfaces in general geometries with or without a static core hole. The formulas are quite involved with many infinite integrals and this is a major barrier for people to apply them in practice. With the purpose of making the calculations easier to perform, we have developed software (QUEELS: QUantitative analysis of Electron Energy Losses at Surfaces) that will do this in a user‐friendly way. It is hoped that with this tool at hand, we will be able to more effectively and quickly get a more complete understanding of the importance of these different effects for quantitative analysis of surface electron energy spectra. Copyright © 2004 John Wiley &amp; Sons, Ltd.

A vibrational spectroscopic study of structure evolution of water dissolved in supercritical carbon dioxide under isobaric heating.

A combination of Raman scattering spectroscopy and infrared absorption was applied to investigate the structural evolution of water dissolved in supercritical carbon dioxide under isobaric heating (T=40-340 degrees C, P=250 bar). Quantitative analysis of experimental spectra allowed us to determine that at relatively moderate temperatures water dissolved in CO(2)-rich phase exists only under monomeric form (solitary water surrounding by CO(2) molecules), but hydrogen-bonded species, namely, dimers, begin to appear upon heating. At the same time, the ratio of dimers to monomers concentration increases with further temperature increase and at temperatures close to the temperature of total miscibility of the mixture (T=366 degrees C, P=250 bar), water dimers only are present in the CO(2)-rich phase.

The role of Zn in the interplay among Langmuir–Blodgett multilayer and myelin basic protein: a quantitative analysis of XANES spectra

We have performed a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the Zinc K-edge of systems formed by phospholipid Langmuir–Blodgett multilayers (LBMLs) in the presence and in the absence of myelin basic protein (MBP) and in two hydration conditions. These spectra have been analysed by a new procedure called Minuit XANes (MXAN) which is able to perform a quantitative fit of XANES data in terms of structural parameters. By this method, we have been able to correlate the relevant differences between the spectra observed in the XANES range with the coordination changes due to reduction of the space around the Zinc when the level of hydration is lowered and/or the myelin basic protein is added. These spectral differences are peculiar of the XANES energy range, and are not present in the extended X-ray absorption fine structure (EXAFS) energy range where the analysis was previously performed. With this investigation, we give an unambiguous answer to the question of the role of zinc in such complexes by showing that the metal interacts with both the phospholipid heads of the substrate and the myelin basic protein.

Evaluation of analytical decoupling for quantitative analysis of high-resolution NMR spectra

A data processing method for obtaining decoupled high-resolution NMR spectra in the weak scalar coupling approximation is evaluated for quantitative analysis. NMR simulations are performed for various sets of parameters and show the potentials and limits of this method, called analytical decoupling. Pour citer cet article : É. Baguet, S. Akoka, C. R. Chimie 7 (2004).

Binding effect of Cu(2+) as a trigger on the sol-to-gel and the coil-to-helix transition processes of polysaccharide, gellan gum.

The binding effect of divalent cation Cu(2+) on the gelation process with a coil-helix transition in Cu(2+)/gellan aqueous solutions has been successfully elucidated by EPR, CD, and viscoelasticity measurements. Generally, Na-type gellan gum in aqueous solution can make gel when accompanied by an intrinsic coil-helix formation induced by hydrogen bonding between chains without any additional cations at T(ch)(-)(in) ( approximately 29 degrees C) with cooling temperature. An extrinsic coil-helix transition, induced by additional divalent cations in advance of the intrinsic sol-gel transition of gellan gum, is separately detected by CD measurement. The extrinsic coil-helix transition temperatures T(ch)(-)(ex) (>47 degrees C), which increased with the Cu(2+) concentration added, were nearly identical to the sol-gel transition temperature, T(sg), determined by the viscoelasticity measurement. Judging from the molar ellipticity by CD measurement and quantitative analysis of EPR spectra, it was elucidated that the helix forming process via divalent cations is composed of two steps ascribed to the different origins, i.e., a chemical binding effect via Cu(2+) ions in the initial stage and hydrogen bonds subsequently. Finally, we propose the coil-helix and the sol-gel transition mechanism initiated by the binding effect with the divalent cation, in which the partial chelate formation can cause local formation of helices and junction zones in the vicinity of the chelates at the initial stage of the process and stabilize the helices and the junction zones. On the other hand, the stabilized helices and junction zones can induce further formation and further stabilization of the Cu(2+)-gellan chelates. The mutual stabilization promotes the formation of three-dimensional network structure at the higher temperature than the intrinsic temperature for network formation.

Quantitative analysis of the X-ray photoelectron spectra of zirconium and zirconium oxide

A procedure for evaluation of XPS spectra is presented that allows the determination of intrinsic and extrinsic contributions to the spectra. It is based on convolution of physically realistic functions for the X-ray energy distribution, the core-level main peak, the cross sections for intrinsic and extrinsic excitations and instrumental broadening. Surface effects have been accounted for by describing the material as a bulk substrate covered with a surface layer of the same material but with different excitation properties. The procedure has been applied to angle resolved Zr 3d spectra of pure zirconium and pure zirconium oxide. The results show that in the case of Zr about 28% and in the case of ZrO 2 about 21% of the total intrinsic intensity of the Zr 3d spectrum is not contained in the main peak.