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•5 years of XPS results highlighting common charge referencing methodologies.•Adventitious carbon (AdC) C 1s binding energy of 284.91 eV, Std. Dev. 0.25 eV found.•Use of AdC, noted as ...problematic by many, gave satisfactory results in 95% of cases.•Differential charging common issue - includes studies assessing AdC binding energies.•Sample electrical isolation improves results by mitigating differential charging.
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.
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•The Gaussian-Lorentzian sum (GLS) and product (GLP) functions are explained.•The Central Limit Theorem is used to justify the use of ‘mixture’ functions for XPS peak fitting.•Plots ...of the GLS and GLP with different values of the mixing parameter, m, are shown.•The GLS is shown to be similar in shape to the Voigt function.•Both the GLS and GLP have their place in XPS peak fitting.
X-ray photoelectron spectroscopy (XPS) is arguably the most important vacuum technique for surface chemical analysis, and peak fitting is an indispensable part of XPS data analysis. Functions that have been widely explored and used in XPS peak fitting include the Gaussian, Lorentzian, Gaussian-Lorentzian sum (GLS), Gaussian-Lorentzian product (GLP), and Voigt functions, where the Voigt function is a convolution of a Gaussian and a Lorentzian function. In this article we discuss these functions from a graphical perspective. Arguments based on convolution and the Central Limit Theorem are made to justify the use of functions that are intermediate between pure Gaussians and pure Lorentzians in XPS peak fitting. Mathematical forms for the GLS and GLP functions are presented with a mixing parameter m. Plots are shown for GLS and GLP functions with mixing parameters ranging from 0 to 1. There are fundamental differences between the GLS and GLP functions. The GLS function better follows the ‘wings’ of the Lorentzian, while these ‘wings’ are suppressed in the GLP. That is, these two functions are not interchangeable. The GLS and GLP functions are compared to the Voigt function, where the GLS is shown to be a decent approximation of it. Practically, both the GLS and the GLP functions can be useful for XPS peak fitting. Examples of the uses of these functions are provided herein.
Plastics and beaches: A degrading relationship Corcoran, Patricia L.; Biesinger, Mark C.; Grifi, Meriem
Marine pollution bulletin,
2009, 2009-Jan, 2009-1-00, 20090101, Letnik:
58, Številka:
1
Journal Article
Recenzirano
Plastic debris in Earth’s oceans presents a serious environmental issue because breakdown by chemical weathering and mechanical erosion is minimal at sea. Following deposition on beaches, plastic ...materials are exposed to UV radiation and physical processes controlled by wind, current, wave and tide action. Plastic particles from Kauai’s beaches were sampled to determine relationships between composition, surface textures, and plastics degradation. SEM images indicated that beach plastics feature both mechanically eroded and chemically weathered surface textures. Granular oxidation textures were concentrated along mechanically weakened fractures and along the margins of the more rounded plastic particles. Particles with oxidation textures also produced the most intense peaks in the lower wavenumber region of FTIR spectra. The textural results suggest that plastic debris is particularly conducive to both chemical and mechanical breakdown in beach environments, which cannot be said for plastics in other natural settings on Earth.
▶ Practical approach to deconvolution of complex X-ray photoelectron 2p spectra of Cr, Mn, Fe, Co and Ni species. ▶ Full disclosure of peak-fitting parameters presented as these are needed to ...reproduce fitting procedures. ▶ Comparison to quality standard samples provides best opportunity to understand species present. ▶ This approach takes into account peak asymmetries, multiplet splitting, shake-up and plasmon structures. ▶ A significant improvement over single peak binding energies used by databases for these species.
Chemical state X-ray photoelectron spectroscopic analysis of first row transition metals and their oxides and hydroxides is challenging due to the complexity of their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Our previous paper M.C. Biesinger et al., Appl. Surf. Sci. 257 (2010) 887–898. in which we examined Sc, Ti, V, Cu and Zn species, has shown that all the values of the spectral fitting parameters for each specific species, i.e. binding energy (eV), full wide at half maximum (FWHM) value (eV) for each pass energy, spin–orbit splitting values and asymmetric peak shape fitting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quantitative chemical state analysis. A more consistent, practical and effective approach to curve fitting was developed based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate literature databases and/or a compilation of literature references and (3) specific literature references where fitting procedures are available. This paper extends this approach to the chemical states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chemical states of these elements poses unique difficulties for chemical state analysis. The curve fitting procedures proposed use the same criteria as proposed previously but with the additional complexity of fitting of multiplet split spectra which has been done based on spectra of numerous reference materials and theoretical XPS modeling of these transition metal species. Binding energies, FWHM values, asymmetric peak shape fitting parameters, multiplet peak separation and peak area percentages are presented. The procedures developed can be utilized to remove uncertainties in the analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.
Redox-active organic compounds have been studied as corrosion inhibitors for steel. Even though it is clear that chemical interactions at the organic–metal oxide interface are behind this inhibitive ...process, the detailed mechanism is not yet fully understood. Using phenyl-capped aniline tetramer (PCAT), we have elucidated the interactions at the interface with iron oxide. We demonstrate the partial reduction of fully oxidized PCAT and the partial oxidation of fully reduced PCAT upon interaction with iron oxide. X-ray photoelectron spectroscopy reveals the appearance of charged nitrogen structures in PCAT deposited on hematite. Iron oxide films in contact with reduced PCAT show a higher conductance due to the introduction of defects, resulting in n-doping. In contrast, the iron oxide film in contact with oxidized PCAT shows a lower conductance, indicating that defects in the film are removed via oxidation, thus reducing the doping level. This is consistent with accepted models for corrosion inhibition, in which PCAT assists in the formation of a passive oxide film. These results are indicative of interfacial charge transfer between PCAT and iron oxide. The extent of the charge transfer and the direction of redox processes depend on the oxidation state of the molecules, enabling the construction of redox-active devices, including sensors and switches.
A current interpretation of XPS spectra of Ni metal assumes that the main 6
eV satellite is due to a two hole c3d
94s
2 (c is a core hole) final state effect. We report REELS observation in AES at ...low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6
eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6
eV and the broad satellite centred at around 861
eV to the cd
9L and the unscreened cd
8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)
2, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni
2+ and Ni
3+ simulate the main line and satellite structures for Ni(OH)
2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.
A CNT-AuNP hybrid has been synthesized through the Michael addition reaction between thiol-functionalized single-wall CNT and small water-soluble Maleimide-AuNP. The resilience and stability of this ...hybrid nanosystem is ensured by a covalent bond linking the nanoparticle to the CNT and by the fact that the functionalization reaction involves the organic shell of the AuNP and not its metallic core.
•The role of Mo on passivation was investigated by AESEC coupled with XPS.•Mo enriched on the surface in the low potential domain and dissolved congruently in the high potential domain.•Enrichment of ...Mo in the low potential domain enhanced the barrier properities of passive film.•The dominant Mo species in the low potential domain was Mo(IV) and that in the high potential domain was Mo(VI).
The beneficial effects of Mo on passive film formation were investigated for Ni22Cr10Mo with AESEC and XPS by comparison with Ni22Cr and pure Ni and Mo. Both spontaneous (E ≈ -0.2 VSCE) and anodic passivation (E = 0.3 VSCE) showed Cr surface accumulation, while significant Mo accumulation (as Mo(IV)) only occurred during spontaneous passivation with a markedly reduced open circuit corrosion rate as a consequence. Mo facilitated the active to passive transition in the low potential domain probably by favoring the oxidation of Cr to Cr2O3 over Cr(OH)3. At higher potential, Mo dissolved as Mo(VI) and did not accumulate in the film.
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