Wagner Plot Research Articles

Study of Defect-Induced Chemical Modifications in Spinel Zinc-Ferrites Nanostructures by In-Depth XPS Investigation

Spinel zinc ferrite nanomaterials with exceptional physiochemical properties are potential candidates for various applications in the energy and environmental fields. Their properties can be tailored using several methods to widen their applications. The chemical combustion approach was followed to prepare the spinel zinc ferrite nanomaterials, which were then subjected to thermal treatment at a fixed temperature. Thermal heat treatment at a fixed temperature was used to evaluate the phase and morphological characteristics of the prepared spinel zinc−ferrite nanocomposites. Various techniques were employed to examine the samples, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS and X-ray−induced Auger electron spectroscopy were used to extensively examine the surface characteristics of the zinc−ferrite. To study the actual chemical states of the synthesized spinel zinc ferrite nanomaterials and the defects created during the thermal treatment, an extensive investigation of the kinetic energy of the X-ray−induced Zn L3M45M45 and Fe L3M45M45 was conducted. Finally, a detailed analysis of the Wagner plot using the modified Auger parameter was performed to verify the exact chemical states of Zn and Fe. Thus, the findings of the investigation show that XPS is a promising and powerful technique to study the composition and chemical states of spinel zinc ferrites, providing an understanding of changes in their properties for functional applications.

XPS photoelectron lines, satellite structures and Wagner plot of Cu(II) β-diketonato complexes explained in terms of its electronic environment

A series of copper(II) β-diketonato complexes [Cu(R1CHCOCHR2)2], with R1 = R2 = C6H5 (1); R1 = C6H5 and R2 = CH3 (2); R1 = R2 = CH3 (3); R1 = C6H5 and R2 = CF3 (4); R1 = CH3 and R2 = CF3 (5) and R1 = R2 = CF3 (6), was subjected to a systematic XPS study of the Cu 2p core-level photoelectron lines, their satellite structures and the LMM Auger lines. The binding energies of the main Cu 2p core-level photoelectron lines are sensitive towards chemical environment (initial state effects) and are described by linear correlations with the combined Gordy scale group electronegativity of the R-groups on the β-diketonato ligands, ΣχR, and the first electrochemical reduction potential, Epc, of the Cu compounds. The modified Auger parameters were determined from the constructed Wagner plot of the copper(II) β-diketonato complexes, which also showed that the initial state effects are dominant during the photoemission process.

Chemical-state analyses of Ni, Zn, and W ions in NiWO4–ZnWO4 solid solutions by X-ray photoelectron spectroscopy

The chemical states of Ni, Zn, and W in microcrystalline NiWO4–ZnWO4 solid solutions were studied by X-ray photoelectron spectroscopy. The recorded spectra of the Ni 2p, Zn 2p, and W 4f photoelectron lines and Ni L2M23M45, Zn L3M45M45, and W N4N67N7 Auger-transition lines show pronounced changes with increasing Zn concentration. The positions of the resolved photoelectron and Auger-transition lines were combined to construct so-called chemical-state plots (Wagner or Auger-parameter plots) for metal ions in solid solutions. With increasing Zn concentration, the Auger parameter increases for Ni and decreases for W, thus evidencing a lowering and an increase of the electronic polarizability around core-ionized Ni and W ions, respectively. At the same time, the character of Zn–O bonds and the local structure around Zn ions do not change. It is concluded that the dilution of NiWO4 with Zn ions is accompanied by an increase of the Ni–O bond ionicity and an increase of the W–O bond covalency. These changes are attributed to the charge redistribution among [NiO6] and [WO6] structural units. We show that a careful in-depth analysis of XPS data obtained with a laboratory-based X-ray photoelectron spectroscopy system can give chemically sensitive, qualitative information on the changes in the first coordination spheres of each metal ion. This information is otherwise accessible only by synchrotron-based techniques (such as X-ray absorption spectroscopy).

The high activity of mesoporous Ga-SiO2 catalysts in the upgrading of glycerol to solketal explained by in-depth characterization

Mesoporous Ga-silicates were prepared using a sustainable and continuous aerosol synthesis procedure. The novel solids showed record activity in the synthesis of solketal from glycerol and acetone. Three different Si/Ga ratios of 34, 74 and 148 were investigated and all materials displayed favorable features for catalytic applications such as high surface area and calibrated mesoporosity. An in-depth characterization allowed to elucidate the remarkable catalytic performance. The insertion of Ga predominantly as single site in tetrahedral coordination in the silica framework was highlighted by X-ray photoelectron spectroscopy (XPS), using the Auger parameter of Ga in a Wagner plot representation. The speciation of Ga was further clarified using solid state 71Ga NMR spectroscopy, confirming the formation of mainly isolated Ga species. Consistently, the aerosol-made Ga-silicates displayed outstanding turnover frequencies (up to 677 h−1) and selectivity, markedly outcompeting other reference metallosilicate catalysts reported in literature. Moreover, the most active catalyst was successfully reused in multiple catalytic cycles thus proving its stability under the selected reaction conditions.

Theoretical double-core-hole spectroscopy of cytosine tautomers

Double-core-hole potentials of cytosine tautomers were calculated within the framework of the density functional theory. The differences between the relaxation energies of these tautomers were visualized using a Wagner plot. Relationship of molecular structure with relaxation energies among tautomers was discussed.

Advanced analysis of copper X‐ray photoelectron spectra

Chemical state X‐ray photoelectron spectroscopic analysis of copper species is challenging because of the complexity of the 2p spectra resulting from shake‐up structures for Cu(II) species and overlapping binding energies for Cu metal and Cu(I) species. This paper builds upon and extends previously published X‐ray photoelectron spectroscopy curve‐fitting and data analysis procedures for a wide range of copper containing species. Steps undertaken include the following: (i) an examination of existing Cu 2p3/2 main peak and Cu 2p3/2 – Cu L3M4,5M4,5 Auger parameter literature data, (ii) analysis of a series of quality standard samples, (iii) curve‐fitting procedures for both the Cu 2p3/2 and the Cu L3M4,5M4,5 spectra (as well as associated anions), (iv) calculations that determine the amount of Cu(II) species in a mixed oxidation state system, (v) calculations and necessary data for thin film mixed oxide/hydroxide thickness measurements, and (vi) a presentation of literature and standard sample values in a Wagner (chemical state) plot. Copyright © 2017 John Wiley & Sons, Ltd.

比較的大きな分子に対する内殻二重正孔分光

The ionization energies of single, double, and triple core-hole (SCH, DCH, and TCH) states were calculated for three isomers of aminophenol with the framework of density functional theory. Our calculated single core-hole ionization potentials were consistent with experiment and the previous theoretical values. Core-ionization energies via complex processes were also estimated. The difference of relaxation energy of two-site DCH (tsDCH) states can be visualized using Wagner plots. We found that the electron density of π orbitals on benzene ring are relaxed to core-vacancy sites at N,O tsDCH state.

Double core-hole states in SiX4 (X = F, Cl, Br, and CH3) molecules derived by photoelectron and KLL Auger spectroscopy

SynopsisIn recent years double core-hole states are intensively studied since their chemical shifts provide detailed information about initial-state and relaxation effects in a molecule. We derived the Si 1s−1, 2s−1, and 2p−1 binding energies as well as the Si 2s−2, 2s−1, 2p−1, and 2p−2 double-core hole binding energies of different SiX4 systems in order to derive the chemical shifts. Based on these results we created Wagner plots, which give insight in the initial state and the relaxation effects in the different molecules.

Auger parameter and Wagner plot studies of small copper clusters

We discuss application of the Auger parameter and Wagner plot concepts to the study of small copper clusters deposited on various supports such as C(graphite), SiO2 and Al2O3. We demonstrate that the cluster size and the electronic properties of the support influence the shifts of both the binding energy of the Cu 2p3/2 transition and the kinetic energy of the Cu L3M45M45; 1G Auger transition. We find that the Cu L3M45M45; 1G-2p3/2 Auger parameter and Wagner plot allow one to single out and measure both initial- and final-state effects with a detail which is superior to that achieved in photoemission studies.

X-ray excited Auger transitions of Pu compounds

X-ray excited Pu core–valence–valence and core–core–valence Auger line-shapes were used in combination with the Pu 4f photoelectron peaks to characterize differences in the oxidation state and local electronic structure for Pu compounds. The evolution of the Pu 4f core-level chemical shift as a function of sputtering depth profiling and hydrogen exposure at ambient temperature was quantified. The combination of the core–valence–valence Auger peak energies with the associated chemical shift of the Pu 4f photoelectron line defines the Auger parameter and results in a reliable method for definitively determining oxidation states independent of binding energy calibration. Results show that PuO2, Pu2O3, PuH2.7, and Pu have definitive Auger line-shapes. These data were used to produce a chemical state (Wagner) plot for select plutonium oxides. This Wagner plot allowed us to distinguish between the trivalent hydride and the trivalent oxide, which cannot be differentiated by the Pu 4f binding energy alone.

High surface area zincosilicates as efficient catalysts for the synthesis of ethyl lactate: an in-depth structural investigation.

Novel Zn-MCM-41 mesoporous materials with particle diameters ranging from 20 to 120 nm were successfully prepared following a straightforward synthesis route. The structural and textural properties of the solids were characterized by N2-physisorption, X-ray diffraction, (29)Si MAS-NMR, TEM and EDX. These results allow evidencing the presence of an ordered mesoporous structure with a very high specific surface area. The insertion of zinc as single site species within the silica framework was investigated using XPS via the Auger parameter in a Wagner plot representation. This is the first time that an in-depth investigation of these types of solids using XPS techniques was performed. The presence of Brønsted and Lewis acidity was elucidated by following in the IR the interaction with ammonia and carbon monoxide. The materials were tested for the conversion of dihydroxyacetone into ethyl lactate with good results both in terms of yield and selectivity and the catalytic activity resulted in excellent agreement with IR and XPS analysis.

Effects of M=Si, Ga and Al for Co substitution on the electronic properties of RCo4M as probed by XPS

The electronic properties of RCo5−xMx (R=Er, Sm, Tm; M=Si, Ga, Al; x=0 and 1) compounds were investigated by X-ray photoelectron spectroscopy (XPS). The study was focused on the Co 3s exchange splitting, the valence bands and chemical shifts of the elements from the analyzed compounds. The Co 2p3/2 core-level chemical shifts were described by means of the Auger parameters and Wagner plot. The hybridization between the R 5d6s and M 3sp and 4sp states and Co 3d states leads to a partial filling of the Co 3d band and to a decrease of the Co magnetic moments in comparison with the value in pure Co metal, in good agreement with the magnetic measurements.

Cluster beam deposition of Cu(2-X)S nanoparticles into organic thin films.

Bulk-heterojunction films composed of semiconductor nanoparticles blended with organic oligomers are of interest for photovoltaic and other applications. Cu2-XS nanoparticles were cluster beam deposited into thermally evaporated pentacene or quaterthiophene to create bulk-heterojunction thin films. The nanoparticle stoichiometry, morphology, and chemistry within these all-gas phase deposited films were characterized by X-ray photoelectron spectroscopy (XPS) and electron microscopy. Cu2-XS nanoparticles were (at most) only slightly copper-deficient with respect to Cu2S; ∼2.5 nm diameter, unoxidized Cu2-XS nanoparticles formed in both pentacene and quaterthiophene, as the matrix was not observed to impact the nanoparticle morphology or chemical structure. Cluster beam deposition allowed direct control of the nanoparticle stoichiometry and nanoparticle:organic ratio. Chemical states or Wagner plots were combined with other XPS data analysis strategies to determine the metal oxidation state, indicating that Cu(I) was predominant over Cu(II) in the Cu2-XS nanoparticles.

内殻二重正孔状態に対する理論的研究

The double ionization energies of two-site double core-hole (tsDCH) states were calculated for dicyano molecules and disilyl compounds. For dicyano molecules, the interatomic relaxation energy increases monotonically from negative value toward zero with an increase in the length of the carbon chain. For disilyl compounds, the energy first decreases from positive to negative and then approaches zero with an increase in the length of the carbon chain. The results based on density functional theory agree with those based on Hartree-Fock theory for these systems. Furthermore, the double ionization energies of single-site DCH and tsDCH states were calculated for XHm-YHn (X,Y: C,N,O,F; m,n = 0–3) systems and their fluorine substituted compounds. Using Wagner plots, initial bonding and final relaxation effects were clearly visualized.

ChemInform Abstract: The Wagner Plot and the Auger Parameter as Tools to Separate Initial‐ and Final‐State Contributions in X‐Ray Photoemission Spectroscopy

AbstractReview: 152 refs.

The Wagner plot and the Auger parameter as tools to separate initial- and final-state contributions in X-ray photoemission spectroscopy

The application of the Wagner plot and Auger parameter concepts as tools for the identification of chemical states of atoms in molecules or solids is growing steadily in the surface science literature. In several publications, however, the chemical and physical insights provided by such conceptual tools are not fully investigated. In this contribution it is shown how easy is to use the Wagner plot to get information on the local valence charge and Madelung (molecular) potential (initial-state effects) and on the extra-atomic relaxation energy gained from the environment (final-state effects) for a core-ionized atom. To cover the gap with previous reviews on the applications of the Wagner plot and the Auger parameter concepts, a brief overview of the contributions which appeared in the literature in the last 15years is presented.

Polarization and site dependence of interatomic relaxation effects in double core hole states

The interatomic relaxation (IR) effects of two-site double core hole (tsDCH) states in selected molecules with a polarizable unit have been systematically investigated using ab initio calculations. The IR effects are analysed by varying the size of this polarizable unit and its position relative to the DCHs. The systems with the DCHs located on the opposite sides of the polarizable unit show large negative IR energies, while those on the same side of the polarizable unit have smaller negative IR effects. Here, the IR energies can even be positive if the polarizable unit is large enough. The generalized Wagner plots of tsDCH states are used to visualize the trend of the IR effects in the molecules studied.

Carbon Free Nickel Subsurface Layer Tessellating Graphene on Ni(111) Surface

The electronic structure of the interface graphene/Ni(111) substrate is reinterpreted based on X-ray photoelectron spectroscopy depth profile study. Using a newly developed Argon gas cluster ion beam sputtering system, we probed the variation of C 1s, Ni 2p core level peaks, valence band, and Ni L3M45M45 Auger transition lines described within Wagner plot methodology with the aim to shed light on the graphene growth mechanism on nickel substrate. We found the presence of thin carbon free nickel subsurface layer located between graphene layers and bulk nickel carbide. The gradient change in the d-band electronic structure through this subsurface layer affects the intrinsic properties of nickel substrate (carbon solubility and diffusivity) and may play a crucial role in the graphene growth mechanism.

Measurement of the Auger parameter and Wagner plot for uranium compounds

In this study, the photoemission from the U 4f7/2 and 4d5/2 states and the U N6O45O45 and N67O45V x-ray excited Auger transitions were measured for a range of uranium compounds. The data are presented in Wagner plots and the Auger parameter is calculated to determine the utility of this technique in the analysis of uranium materials. It was demonstrated that the equal core-level shift assumption holds for uranium. It was therefore possible to quantify the relative relaxation energies, and uranium was found to have localized core-hole shielding. The position of compounds within the Wagner plot made it possible to infer information on bonding character and local electron density. The relative ionicity of the uranium compounds studied follows the trend UF4 > UO3 > U3O8 > U4O9/U3O7 ≈ UO2 > URu2Si2.

Thin film characterisation of chromium disilicide

The ambiguous binding energy (BE) shift of the Cr 2p3/2 peak of chromium disilicide with respect to the one of pure Cr metal in the X-ray photoelectron spectroscopy (XPS) has meant difficulties in practice for silicide determination. In the present study, with the aid of an interconnected ultrahigh vacuum (UHV) system for silicide fabrication and characterisation, high purity Cr–Si thin films with thickness around 100nm and well-controlled chemistry were produced. The characteristics with respect to chemical composition and phase identity were determined by means of XPS and X-ray diffraction (XRD). The experimental results were also compared with predictions using thermodynamic effective heat of formation (EHF) model. Whilst the BE positions of the core-level Cr 2p3/2 peak of Cr and CrSi2 are close to each other, larger shifts are determined for their corresponding L3M23M23 Auger transitions. By establishing a chemical-state plot, or the so-called Wagner plot, it is illustrated that the core-level shift caused by the initial-state effects is basically compensated by the one owing to the final-state effects, resulting in a small negative BE shift of the Cr 2p3/2 peak from metallic state to disilicide state. The valence band spectra were also investigated and correlated to the core-level spectra.