Auger Parameter Research Articles

Monovalent nickel ion as ionization probe in matrix-assisted laser desorption/ionization mass spectrometry

We have developed NiO/HM20, a matrix composed of NiO nanoparticles (NiO) loaded on zeolite surface, for matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). By photoexcitation, monovalent nickel ion (Ni+) was dominantly observed with high intensity. The mechanism of Ni+ production was studied by picosecond time-resolved emission spectroscopy. By loading NiO on the zeolite surface, a new relaxation pathway to other electronic excited states was observed, which increased the lifetime of electron–hole pairs and promoted the reduction of nickel. The long-lived charge-separated electronic excited state corresponding to the large polarization of NiO was confirmed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD). The correlation between the Auger parameter related to the polarization energy and the Ni+ peak intensity in the mass spectrum was confirmed. By applying the developed NiO/HM20 matrix to the MS measurement of small molecules, we found that molecules were ionized through complex formation with Ni+ using the coordination of lone electron pairs or π-electrons in the analyte molecules.

Development of the NIST X-ray Photoelectron Spectroscopy (XPS) Database, Version 5

It has been over 20 years since the National Institute of Standards and Technology (NIST) launched the first web version of its X-ray Photoelectron Spectroscopy (XPS) database (Lee et al., 2002; Wagner, 1991) which has approximately 1000 active users every day. This database was recently redesigned to meet NIST security requirements and to include new features and enhancements. The new application is built upon a relational database using a cross-platform and open-source framework (Henning et al., 2002). In addition to a modern design interface, the new features include custom-built components for displaying formatted molecular formulas and spectral lines, for sorting spectral lines, and for graphical display of chemical shifts of binding energies, Auger-electron kinetic energies, and Auger parameters for elements in different compounds.

Exploiting the Correlation between the 1s, 2s, and 2p Energies for the Prediction of Core-Level Binding Energies of Si, P, S, and Cl species.

The binding energies (BEs) of the 1s, 2s, and 2p core electrons of third-period elements (Si, P, S, Cl) were calculated using Hartree-Fock (HF) and B3LYP, BH&HLYP, and LC-BOP ΔSCF, and the shifted KS ΔSCF methods. Linear relationships between two BEs were derived and compared with the Auger parameter. The derived lines are essentially parallel, with only the intercepts differing. The difference in intercepts is due to the lack of electron correlation effects in HF and the self-interaction errors (SIEs) of the functional. The slope is the slope of the linear relationship between the chemical shifts. The straight lines between the 2s and 2p BEs also coincided with the Auger parameter lines, which have a slope of 1 by definition and an intercept being the difference between the 2s and 2p BEs. The shifted KS ΔSCF scheme compensates for SIEs, yielding equations that are approximately invariant. The calculated average gaps for the 2s and 2p BEs are 51.21 eV for Si, 57.48 eV for P, 63.85 eV for S, and 70.48 eV for Cl. The straight lines representing the relationships between the BEs of the 1s and 2s and 1s and 2p electrons are also parallel to each other in ΔSCF and converge into a single line in the shifted ΔSCF scheme. However, these lines are steeper than the Auger parameter line. The derived relationships can be used to predict unknown BEs, which we have applied to many molecules. The results are highly accurate, with mean absolute errors (MAEs) of less than 0.2 eV compared to experimental values.

Physicochemical and structural properties of silica films prepared from perhydropolysilazane using vacuum ultraviolet irradiation

Developing techniques to form functional films at low temperatures is crucial for enabling their application on materials with limited heat resistance. In this study, silica films were prepared by irradiating a perhydropolysilazane (PHPS) precursor, which contains reactive Si–H and N–H groups and is free from organics, with vacuum ultraviolet (VUV) light under a controlled atmosphere. To investigate the quality of the resulting films and mechanisms behind photochemical conversion, infrared and electron spectroscopic measurements were performed. The results revealed that VUV irradiation converted the top surface of the film into silica, irrespective of the atmospheric conditions. However, differences in the oxygen concentration affected both the VUV light intensity penetrating the film and the oxygen diffusion into it, leading to the formation of silica or silicon oxynitride within the film. Under irradiation, PHPS was converted to silica not only from the surface but also from the interface with the substrate. In addition, silica was formed even at long irradiation distances, in which case VUV light barely reached the PHPS surface owing to absorption by atmospheric oxygen. These findings demonstrate that the silica-film formation involved two processes: breaking of chemical bonds induced by VUV photons and oxidation due to oxygen diffusion from the surface. The spectroscopic measurements and X-ray reflectivity results indicated that the composition, chemical state, Auger parameter, and density of the prepared silica film were comparable to those of a silica film prepared through heat treatment at 500°C. Further, the prepared silica film using VUV irradiation had a smoother surface than that of the heat-treated film. The thickness of the prepared film remained unchanged before and after VUV irradiation, indicating that the formation process using VUV irradiation suppressed the shrinkage of the film during the conversion of PHPS to silica.

Influence of TiO2 coverage on activity and stability of Pd-TiO2/MWCNT-supported catalysts used in direct formic acid fuel cells

Pd and TiO2 supported on functionalized multiwall carbon nanotubes (f-MWCNTs) catalysts were investigated in formic acid electrooxidation reaction in direct formic acid fuel cell. TiO2 (5–60 wt.% loading) on f-MWCNTs was deposited using microwave-assisted hydrothermal method. 20 wt.% of Pd was deposited on TiO2/f-MWCNTs by reduction of palladium (II) chloride salt with sodium borohydride. Catalysts’ structure and composition were characterized by XRD, STEM, HR-TEM, TGA, XPS/XAES (Pd, Ti, O spectra features, density of valence states, Auger parameters). Average crystallite size of Pd and TiO2 from XRD (3–4 nm) agrees with those by HR-TEM (3–5 nm). Low TiO2 coverages (below 32wt.%) show smaller crystallites due to increased surface hydrophilicity, higher amount of TiO2 oxygen vacancies with attached Pd nanoparticles, increased density of valence states of strong Pd–TiO2 interface. In contrary, the higher coverages indicate lower amount of Pd–O–Ti, Ti–O–C, Pd–O–C interfaces, with electron charge transfer from TiO2 to f-MWCNTs, and to Pd. Catalysts activity (40–106 mWmgPd−1) and stability (5–240 h) are enhanced at low TiO2 coverages (4–8 wt.%) due to a strong Pd-TiO2 interface on oxygen vacancies, improved electron transport and a high active surface area. Oscillatory self-cleaning mechanism of Pd is due to oxidation by -OH groups (TiO2, f-MWCNTs), and hydrogen and CO spillover.

The development of laboratory‐based high energy sources for XPS

Over the last fifty years, a number of higher energy X‐ray sources have been suggested as alternatives for the usual AlKα source found in the first commercial XPS systems and still the standard anode material for XPS today. This paper reviews the development of a number of such sources, predominantly in the authors' laboratory, and the rationale behind the desire to extend the binding energy range of the technique. The achromatic sources SiKα, ZrLα and TiKα are described along with monochromatic sources AgLα and CrKβ, both based on the standard quartz monochromator geometry but taking higher orders of diffraction. The driving force for much of this development was the desire to probe deeper core levels and CCC Auger transitions. These could be combined into initial or final state Auger parameters as described in much of the work cited in this review. The highest energy source considered is the CuKα source based around an external X‐ray tube, which provides much insight into the electronic structure of steels by measurement of the Fe1s and FeKLL peaks. The last decade or so has seen a significant increase of interest in HAXPES, and all manufacturers of turn‐key XPS instruments offer HAXPES options of one form or another, there are three dedicated HAXPES systems commercially available, which are very briefly described.

Core hole electron screening in InSb

The application of a potential model to the analysis of differences between the Auger parameters of InSb and the elemental materials yields a value 1.82±0.07Å for the core hole screening distance in InSb. It also yields a value of 0.22 ± 0.49 e for the charge transfer in InSb. Shifts in the Auger parameters of elements between their metallic states and in a compound semiconductor are interpreted using a novel method based on quantifying atomic core potential, as a quantum mechanical observable, in terms of its dependence on the valence charge and the number of atomic core holes. The core hole screening distance is ∼30% larger than half the interatomic distance between the nearest neighbors and, by the equivalent cores model, is expected to be the screening radius of Sn and Te impurities in InSb.

Development of a Vertical Mashing Machine and Specifying its Main Parameters

The paper proves the necessity to create new modernized types of fruit and vegetable processing machines. The paper highlights the importance of such machinery versatility, since each individual type of fruit and vegetable has its own physical characteristics, such as solidity, viscosity, moisture content, fibers, seeds, and grains. (Research purpose) To study the zucchini mashing process performed by the developed vertical mashing unit. (Materials and methods) An improved mashing machine design is proposed: a vertical plant with a conical auger inside and a sieve drum. (Results and discussion) Based on the calculations, the following parameters are specified: the body wall thickness, the cell diameter, the cone and conical auger parameters, as well as the machine operating modes. The sieve drum height is set at 0.8 meters, the diameter is 0.4 meters, the distance between the cone top and the drum is 0.15 meters. A conical auger is made for four working turns. (Conclusions) The minimum number of zucchini seeds (100 pieces) is specified for the subsequent selection of the drum cell diameter. The criteria and delimitations for high-quality zucchini mashing were identified. The diameter of the vertical masher cells was set within the range from 0.0071 to 0.0093 meters.

Resolving Oxidation States and X–site Composition of Sn Perovskites through Auger Parameter Analysis in XPS (Adv. Mater. Interfaces 7/2023)

Resolving Chemical States in Sn-Based Perovskites In article 2201828, Alexander Wieczorek, Sebastian Siol, and colleagues demonstrate how Auger parameter analysis enables more reliable chemical state analysis of Sn-based perovskites. Through systematic compositional variation a high sensitivity of this parameter on the X-site composition and oxidation state of Sn-based perovskites is demonstrated. The latter aspect can be used to detect and understand aging of these compounds under ambient conditions. This approach can be easily adopted using standard XPS equipment and enables better reproducibility of results across laboratories. [Artwork by Alexander Wieczorek]

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.

Detailed peak fitting analysis of the Ni 2p photoemission spectrum for metallic nickel and an initial oxidation

A quantitative study of the surface composition of clean metallic and partially oxidized nickel exposed to oxygen was carried out employing X-ray photoelectron spectroscopy (XPS). By fitting both branches of the metallic Ni 2p spectrum, it was possible to resolve two previously unreported satellite peaks in the Ni 2p1/2 portion of the spectrum. For the partial oxidation of the nickel surface, we analyzed the Ni 2p, O 1s, and C 1s angle-resolved XPS spectra. Using state-of-the-art peak-fitting (including the block approach) and background modeling methods (including the active approach) it was possible to discriminate the peaks of Ni2O3 from those of metallic nickel for both branches of the Ni 2p spectra from partially oxidized nickel. The oxidation of metallic nickel is through the formation of a Ni+3 oxide layer together with deep protrusions. The uncertainties are calculated with the covariance matrix method. The strong overlap and shape similarity of the Ni0 L3M45M45 Auger structure with that of the Ni+3 strongly suggests that the modified Auger Parameter does not provide direct additional insight about the chemical state to that provided by the photoemission spectra.

Resolving Oxidation States and X–site Composition of Sn Perovskites through Auger Parameter Analysis in XPS

AbstractReliable chemical state analysis of Sn semiconductors by XPS is hindered by the marginal observed binding energy shift in the Sn 3d region. For hybrid Sn‐based perovskites especially, errors associated with charge referencing can easily exceed chemistry‐related shifts. Studies based on the modified Auger parameter α ′ provide a suitable alternative and have been used previously to resolve different chemical states in Sn alloys and oxides. However, the meaningful interpretation of Auger parameter variations on Sn‐based perovskite semiconductors requires fundamental studies. In this work, a comprehensive Auger parameter study is performed through systematic compositional variations of Sn halide perovskites. It is found that in addition to the oxidation state, α ′ is highly sensitive to the composition of the halide site, inducing shifts of up to Δα ′ = 2 eV between ASnI3 and ASnBr3 type perovskites. The reported dependencies of α ′ on the Sn oxidation state, coordination and local chemistry provide a framework that enables reliable tracking of degradation as well as X‐site composition for Sn‐based perovskites and related compounds. The higher robustness and sensitivity of such studies not only enables more in‐depth surface analysis of Sn‐based perovskites than previously performed, but also increases reproducibility across laboratories.

X-ray Diffraction, Micro-Raman and X-ray Photoemission Spectroscopic Investigations for Hydrothermally Obtained Hybrid Compounds of Delafossite CuGaO2 and Wurtzite ZnO

P-type delafossite CuGaO2 is a wide-bandgap semiconductor for optoelectronic applications, and its lattice parameters are very similar to those of n-type semiconductor wurtzite ZnO. Accordingly, the investigation of crystalline heterostructures of CuGaO2 and ZnO has attracted significant attention. In this study, interfacial CuGaO2/ZnO hetero-compounds were examined through X-ray diffraction (XRD) analysis, confocal micro-Raman spectroscopy, and X-ray photo-electron spectroscopy (XPS). XRD and Raman analysis revealed that the hydrothermal deposition of ZnO on hexagonal platelet CuGaO2 base crystals was successful, and the subsequent reduction process could induce a unique, unprecedented reaction between CuGaO2 and ZnO, depending on the deposition parameters. XPS allowed the comparison of the binding energies (peak position and width) of the core level electrons of the constituents (Cu, Ga, Zn, and O) of the pristine CuGaO2 single crystallites and interfacial CuGaO2/ZnO hybrids. The presences of Cu2+ ions and strained GaO6 octahedra were the main characteristics of the CuGaO2/ZnO hybrid interface. The XPS and modified Auger parameter analysis gave an insight into a specific polarization of the interface, promising for further development of CuGaO2/ZnO hybrids.

Applying monochromated silver X‐rays to the surface characterization of silicon‐containing materials

Although the use of a monochromated silver X‐ray source for X‐ray photoelectron spectroscopy (XPS) analysis was first reported in the 1980s, it has found limited application. Two important advances have been made in recent years that now enable it to be used more routinely for surface analysis. These advancements are the development of relative sensitivity factors for quantification and the fully motorized dual silver/aluminum X‐ray source, which enables the change to monochromated X‐ray energies in a few minutes versus hours. Silicones are an important class of materials that have unique chemical properties that can vary from liquids to glass‐like materials. XPS, with monochromatic Al Kα X‐rays, is used routinely to characterize silicon‐containing materials and to identify different silicone functional groups. This was aided by the work published on the analysis of Si 2p peaks acquired from polysiloxane materials. The binding energy increases nonlinearly when methyl groups on a silicon atom are replaced by oxygen atoms. This work will now be extended to determine the binding energy shifts in Si 1s, 2s, and Auger spectra, which will allow the identification of silicon chemistry when using monochromated silver X‐rays. The Auger parameters of the different polysiloxanes will be compared to those of other silicon‐containing materials. Comparison of the depth of analysis in silicon‐containing materials when changing from aluminum to silver X‐rays will also be addressed.

X-ray Photoelectron Spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Insight into the Pathways of Manganese Oxalate Thermal Decomposition to MnO and MnCO3.

X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to study the isothermal decomposition of MnC2O4 under ultrahigh vacuum and N2 environmental conditions, respectively. High-resolution core-level XP spectra, X-ray-induced Auger spectra, and infrared spectra were obtained as a function of annealing time. In XPS studies, the time-dependent thermal decomposition characteristics were elucidated by analyzing surface composition, chemical shifts, satellites in the Mn 2p3/2 and Mn LMV bands, and Auger parameters for Mn and O. Functional groups developing during the ongoing reaction were identified by DRIFTS from characteristic vibrations. For the first time, the isothermal decomposition of manganese oxalate was shown to proceed via two pathways involving nucleation and accumulation of MnO and MnCO3. The kinetics of the decomposition in vacuum could be described by the Prout-Tompkins or/and by the Avrami-Erofeev models. The results obtained by XPS, DRIFTS, and ex situ XRD allowed concluding that the final product of oxalate decomposition was composed of MnO and MnCO3 or/and unidentate/polydentate carbonate structures populating the surface of the sample. A substantial formation of graphitic carbon was also observed and associated with interface chemical reactivities between the MnO particles and the supporting gold foil.

Multi-dimensional characterizations of washing durable ZnO/phosphazene-siloxane coated fabrics via ToF-SIMS and XPS

The poor washing durability of nylon fabric coating hinders their applications. Here, by spray coating zinc oxide (ZnO) and APESP siloxane on the surface of nylon 6, we find that the washing durability of the coated fabric could be enhanced dramatically. To reveal its mechanism, the microstructure of the fabric was investigated via Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), respectively. It was found that the ratio of ZnO and APESP can significantly influent the acquired fabric morphology. XPS depth profiling results further suggest the crosslinked network of the ZnO/APESP on the fabric surface. Moreover, the formation of Si–O–Zn bonds confirmed by the modified auger parameter can enhance the washing durability of the fabric coating. Moreover, the characterization methods introduced in this paper, in particular the UB mode, which can be applied into ToF-SIMS measurements to obtain 2D mapping and model construction results with higher spatial resolution, thus providing guidelines for future nanoscale researches.

Chemical state analysis of reactively sputtered zinc vanadium nitride: The Auger parameter as a tool in materials design

Photoelectron spectroscopy is an important tool for the development of new materials. However, especially for nitride semiconductors, the formation of surface oxides, surface band bending as well as the lack of a suitable charge reference often prevent a robust analysis. Here, we perform a comprehensive chemical state analysis of the Zn-V-N phase space using the Auger parameter concept, which is less sensitive to such uncertainties. Phase-pure Zn2VN3, VN, and Zn3N2 samples are analyzed in a dual-source lab-based HAXPES system, after transfer in inert-gas atmosphere. XPS and HAXPES measurements are performed using Al kα and Cr kα, respectively. In addition, high-throughput chemical state analysis is performed on combinatorial Zn1-xVxN thin film libraries using conventional XPS. The evolution of the Zn Auger parameter in Zn1-xVxN is consistent with previous mapping of the structural and functional properties. Strikingly, the study reveals a narrower stability range of wurtzite Zn1-xVxN than our previous high-throughput XRD screening, highlighting the sensitivity of the measurement approach. The procedures applied here are transferable to many other material systems and could be particularly useful for the high-throughput development of materials with low crystallinity where insights from XRD screenings are limited.

Accessing the robustness of adventitious carbon for charge referencing (correction) purposes in XPS analysis: Insights from a multi-user facility data review

An assessment of X-ray photoelectron spectroscopy (XPS) results from 1237 samples submitted to a multi-user facility from a five year period investigates the usage and effectiveness of common charge referencing methodologies for insulating samples. Carbon 1s (C 1s) starting peak-fitting routines for common graphitic-like materials and for adventitious carbon (AdC) are presented. An average adventitious carbon (AdC) C 1s binding energy of 284.91 eV (Std. Dev. 0.25 eV) was found for 117 samples that also contained a secondary charge reference possibility. With an understanding of the limits and possible issues with using AdC for charge referencing purposes and by incorporating other methodologies (Auger parameter, checks for data self-consistency, well-established peak-fitting routines) it was found that using AdC C 1s for charge referencing gave satisfactory and meaningful results in 95% of the 522 cases assessed. Differential charging is a common issue including in studies assessing AdC binding energies. This work demonstrates that electrical isolation (floating) of mixed insulating/semi-conducting/conducting samples significantly improves outcomes by mitigating differential charging issues.

Defect induced enhanced catalytic activity of Lu doped titanium dioxide (TiO2) thin films

In this article, we report the property evaluation of Lu doped TiO2 thin films suitable for catalytic activity. The detailed investigation on the film's structural, optical, and chemical properties was carried out. The structural study using XRD and Raman reveal presence of dominant crystalline anatase phase for Lu doped samples. The spherical grains were observed on the surface of Lu doped films and these act as active centres during catalytic activity. XPS analysis confirm the chemical states of basic elements including Ti, O, and Lu, and a brief discussion on enhanced defects on doping using anion and cation core level spectra is described. Moreover, modified Auger parameter and change in chemical bonding interaction energy also strongly supports enhanced defects in the material. These defect centres may act as a trapping core, extending carrier recombination and increasing photocatalytic activity. Under UV irradiation, sample's photocatalytic performance was tested for methyl orange and methylene blue target dyes. Among the samples deposited, 0.4 at% Lu doped films perform better as a photocatalyst, with high degradation efficiency, high reaction rate, and short half-life time.

On the Auger parameter of Cu(II) compounds

The Auger parameter (AP) of Cu(I) halides follow the trend: α′Cu(s) > α′CuI > α′CuBr > α′CuCl > > α′Cu(g), in agreement with the electronic polarizabilities of the nearest‐neighbor ligands of the core‐ionized Cu(I) ion. On the contrary, the AP of Cu(II) halides and other Cu(II) compounds are close to that of copper metal. We extend our simple AP semiempirical model, published in this journal in 2019, to try to understand the unusual results reported for the Cu(II) compounds.