X-ray Photoelectron Spectroscopy Imaging Research Articles

Surface science insight note: Imaging X‐ray photoelectron spectroscopy

Quantification of X‐ray photoelectron spectroscopy (XPS) data is often limited by the heterogeneous nature of the material surface. However, it is often the case that heterogeneous material contains areas within the analyzed area that are effectively homogeneous. In this Insight note, concepts, and methods used to analyze both XPS data are presented to extract both spatial and spectral information from heterogeneous surfaces. These concepts and methods are applied to a specific material surface that contains three chemical compounds separated spatially. The analysis entails converting XPS image data to spectral data and is designed to highlight the potential of XPS imaging in revealing compositional information correlation with spatial information. Properties of algorithms used to evaluate XPS images and spectra are described to outline their application to image data. A case study of an imaging XPS data set is presented that demonstrates how poor signal‐to‐noise images, where the signal is recorded for 4 s per image, are still open to analysis yielding useful information. Ultimately, the methods presented here will aid in interpreting complex XPS data obtained from spatially complex materials often obtained during extensive cycling, such as conventional or electrocatalysts.

Interfacial Nanostructure and Hydrogen Bond Networks of Choline Chloride and Glycerol Mixtures Probed with X-ray and Vibrational Spectroscopies.

The molecular distribution at the liquid-vapor interface and evolution of the hydrogen bond interactions in mixtures of glycerol and choline chloride are investigated using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Nanoscale depth profiles of supersaturated deep eutectic solvent (DES) mixtures up to ∼2 nm measured by ambient-pressure XPS show the enhancement of choline cation (Ch+) concentration by a factor of 2 at the liquid-vapor interface compared to the bulk. In addition, Raman spectral analysis of a wide range of DES mixtures reveals the conversion of gauche-conformer Ch+ into the anti-conformer in relatively lower ChCl concentrations. Finally, the depletion of Ch+ from the interface (probing depth = 0.4 nm) is demonstrated by aerosol-based velocity map imaging XPS measurements of glyceline and water mixtures. The nanostructure of liquid-vapor interfaces and structural rearrangement by hydration can provide critical insight into the molecular origin of the deep eutectic behavior and gas-capturing application of DESs.

Surface analysis insight note. Principal component analysis (PCA) of an X‐ray photoelectron spectroscopy image. The importance of preprocessing

This Insight Note follows two previous Insight Notes on X‐ray photoelectron spectroscopy (XPS) image analysis that dealt with the importance of analyzing the raw data and the use of summary statistics. As a next step in the exploratory data analysis (EDA) of XPS images, we now show principal component analysis (PCA) of an XPS image. PCA is appropriate when the spectra in a data set are correlated to some degree and the noise in the spectra is unimportant. In these cases, PCA can significantly reduce the dimensionality and complexity of data sets. Preprocessing is an important part of many PCAs. Its usefulness is illustrated with a small, mock data set, where the potential pitfalls of not preprocessing are shown. PCAs of XPS image data that were not preprocessed and preprocessed by mean centering are illustrated. Scree plots, which are used to determine the number of abstract factors (principal components, PCs) that describe a data set, are shown. The spectra in our XPS image are quite noisy, which is consistent with the moderate, but still significant, amount of variance that is captured by the first two PCs in our PCA. With both preprocessing methods, the loadings on PC1 and PC2 are remarkably smooth. The loadings on the next six PCs also appear to contain some chemical information. Scores images generated using both no preprocessing and preprocessing by mean centering reveal many of the same general features in the data set that were found in our two previous Insight Notes.

Surface analysis insight note: Analysis of X‐ray photoelectron spectroscopy images with summary statistics

Developments in X‐ray photoelectron spectroscopy (XPS) instrumentation and the need for spatial information in surface characterization have led to advances in XPS imaging and related image processing techniques. In this Insight Note, we demonstrate the use of summary statistics as simple, but effective, tools for understanding XPS hyperspectral images (data cubes) prior to more advanced image processing. An XPS image obtained from a silicon surface patterned with different thicknesses of oxide was analyzed with three summary statistics: a tool in the MATLAB programming environment, the mean, and pattern recognition entropy (PRE). The MATLAB tool largely separates the spectra into two groups. The mean does a somewhat better job differentiating between the spectra, and PRE is even more effective. The results of the MATLAB summary statistic are confirmed by plotting the average and standard deviation spectra of different regions of the image it produces. The results of the mean and PRE summary statistics are confirmed by evenly segmenting the results and examining the average and standard deviation spectra of these segments. Fitting these average spectra demonstrates the greater effectiveness of the PRE summary statistic in segmenting the spectra into chemically distinct groups.

Deposition order and physicochemical process visualization of ink intersections using X‐ray photoelectron spectroscopy imaging for forensic analysis

The physicochemical events at ink intersections are largely understudied. Chemical imaging techniques and multivariate analyses applied to this problem thus far lack the performance characteristics to make confident conclusions about these processes. This deficiency leads to subjective and controversial deposition order determinations in forensic investigations. In this comprehensive report, 44 unique crossings involving laser toners and stamps, as well as felt‐tip, rollerball, gel, and ballpoint pen inks, were imaged with X‐ray photoelectron spectroscopy (XPS), using a 50‐μm X‐ray spot size and 100‐μm steps. The specificity and surface sensitivity of XPS enabled the objective visualization of the inks' chemistry upon deposition via spatial elemental distribution in‐situ. Signal intensity and atomic concentration were mapped for each element detected. Discrimination was possible in 100% of written and printed inks analyzed, and the relationship between the elemental concentration profile in each intersection was compared with the known sequence. Formation of ink layers, mixing, and separation of ink components by way of electrostatic forces were observed. Insights into the known complexity of ink intersection processes were revealed and highlight the need for understanding the chosen analytical technique's information depth and for complementary analyses to increase sequencing confidence. We also provide evidence that these processes invalidate the utility of principal component analysis for analyzing ink intersections. However, sequencing accuracy was 84% for all samples analyzed, and its success was highly dependent on the presence of physical features (i.e., thick coatings and embossed regions). In some intersection types, especially toners, the features exposed with XPS imaging enabled a sequencing accuracy of 100%.

Surface analysis insight note: Initial, statistical evaluation of X‐ray photoelectron spectroscopy images

With advances in instrumentation and image processing, imaging X‐ray photoelectron spectroscopy (XPS) is becoming increasingly important in surface analysis. In this Insight Note, we suggest the following three steps for the initial evaluation of XPS images: (i) Plot all the data. Possible plots here include an overlay plot, a plot of the average and standard deviation of the spectra, a waterfall plot, and a contour plot. (ii) Examine slices through the data cube at different binding energies, identifying those that show significant contrast. (iii) Examine the spectra, including their average and standard deviation, in defined regions of slices through the data that show contrast. These steps allow XPS images to be probed without the use of more sophisticated exploratory data analysis (EDA) techniques. Indeed, these steps may set the stage for additional EDA analysis of XPS images. Furthermore, they provide an initial understanding of an XPS image that stays close to the original data. Our three‐step protocol was applied to an XPS image of a region of a silicon wafer with different oxide thicknesses. This image primarily contained two types of pixels/regions: one of silicon with a thin oxide layer and the other of silicon with a thicker oxide layer. We emphasize the importance of contour plots of all the data and examining the average and standard deviation of regions of contrast in slices through the data cube.

Properties of the fluoroacrylate and methacryloxypropyl-trimethoxysilane applied to a layer of Cu2O on bronze as either single or multi-component coatings

Various coatings have been developed and explored to protect bronze surfaces against the uncontrolled formation of different corrosion products when exposed to outdoor environments.In this research, the surfaces of artificially-formed oxidized bronze patinas (OB), consisting of Cu2O, were covered with either a single-component (fluoroacrylate, FA or methacryloxypropyl-trimethoxysilane, MS) or multi-component (a mixture of FA and MS, FA-MS) fluoropolymer coating and investigated. Variations in the concentration of each component in the coating were studied. Electrochemical tests were performed to determine the corrosion protection efficiency, followed by detailed surface analyses of the OBs, both uncoated and covered with single and multi-component coatings. A variety of investigative methods were used, including focused ion beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS).The coating made from a combination of FA and MS resulted in a very high protection efficiency. Despite the increased hydrophilicity of the single MS component, however, it was shown to efficiently protect the oxidized bronze surface. The FA-MS systems showed high hydrophobicity, but no improvement was measured in the efficiency of the corrosion protection when it was compared to the coating that contained 10% MS. According to XPS and ToF-SIMS imaging, the FA component of the FA-MS coating was not present only on the uppermost surface of the coating but throughout the whole coating, which could affect its corrosion protection efficiency.

2-Phenylimidazole Corrosion Inhibitor on Copper: An XPS and ToF-SIMS Surface Analytical Study

This work presents a surface analytical study of the corrosion inhibitor 2-phenylimidazole (2PhI) adsorbed on a Cu surface from 3 wt.% NaCl solution. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to investigate the surface phenomena. Various XPS experiments were performed, i.e., survey- and angle-resolved high-resolution XPS spectra measurements, gas cluster ion beam sputtering in conjunction with XPS measurements, and XPS imaging in conjunction with principal component analysis. These measurements were used to detail the composition of the surface layer at depth. In addition, various ToF-SIMS experiments were performed, such as positive ion ToF-SIMS spectral measurements, ToF-SIMS imaging, and cooling/heating in conjunction with ToF-SIMS measurements. This study shows that organometallic complexes were formed between 2PhI molecules and Cu ions, that the surface layer contained entrapped NaCl, that the surface layer contained some Cu(II) species (but the majority of species were Cu(I)-containing species), that the surface was almost completely covered with a combination of 2PhI molecules and organometallic complex, and that the temperature stability of these species increases when 2PhI is included in the organometallic complex.

Selective atomic layer deposition on flexible polymeric substrates employing a polyimide adhesive as a physical mask

The rise of low-temperature atomic layer deposition (ALD) has made it very attractive to produce high-κ dielectric for flexible electronic devices. Similarly, selective deposition of ALD films is of great relevance for circuitry. We demonstrated a simple method of using a physical mask to block the film’s growth in selected polymeric and flexible substrate areas during a low-pressure ALD process. A low-cost silicone adhesive polyimide tape was used to manually mask selected areas of bare substrates and aluminum strips deposited by evaporation. 190 cycles of aluminum oxide (Al2O3) and hafnium oxide (HfO2) were deposited at temperatures ranging from 100 to 250 °C. Using x-ray photoelectron spectroscopy (XPS) analysis and energy dispersive x-ray spectroscopy (EDS), we showed that the mask was effective in protecting the areas under the tape. The mask did not show any modification of shape for an exposure of 10 h at 250 °C, hence keeping the form of the masked area intact. An analysis of the unmasked area by ellipsometry (632.8 nm) and x ray shows a regular film with a thickness variation under 2 nm for a given temperature and constant refractive index. EDS, selected-area XPS, and imaging XPS show an evident change of elemental content at the interface of two areas. By XPS, we established that the structure of the films was not affected by the mask, the films were stoichiometric, and there was no effect of outgassing from the adhesive film.

Surface analysis and interface properties of 2-aminobenzimidazole corrosion inhibitor for brass in chloride solution.

This work presents a corrosion study of 2-aminobenzimidazole (ABI) as a corrosion inhibitor for brass in chloride solution. Electrochemical, field emission scanning electron microscopy, atomic force microscopy, and contact angle measurements showed that ABI mitigates brass corrosion after short-, medium-, and long-term immersion periods. Next, a detailed surface analysis of the ABI adsorbed on the brass surface was performed using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) techniques. XPS imaging was performed in association with principal component analysis to determine the different phases on the surface. In order to describe the in-depth composition of the ABI surface, an angle-resolved XPS analysis was performed. This analysis was further supported by gas cluster ion beam sputtering to gradually remove the ABI surface layer, and XPS analysis was performed after each sputtering cycle. Finally, TOF-SIMS analyses showed the formation of Cu/Cu2-ABI and Zn-ABI compounds, the 2D distribution of ABI-related compounds, and their thermal stability on the brass surface. Graphical abstract.

UV fluorescence as a method of high throughput surface cleanliness assessment: A comparison with XPS

UV visible fluorescence (UV–vis) was trialled as a method for the rapid screening of surface cleanliness of metals. By comparing the relative intensity of the fluorescence to the film thickness of the carbonaceous contamination, an evaluation of the effectiveness of UV–vis was made. Surface composition and the thickness of carbon contamination on stainless steel/mineral oil and copper/tallow wax samples was measured with X-ray photoelectron spectroscopy (XPS). After vapour degreasing with trichloroethylene it was found that residual tallow wax was not effectively detected by UV–vis; whereas a commercial mineral oil was readily detected by UV–vis. The reason for the lack of fluorescence is that the tallow wax is largely an unconjugated system, in that it mostly comprises saturated or monounsaturated carbon – carbon bonds, which do not fluoresce. Using imaging XPS an increase in carbon film thickness close to the edge of the sample is observed, a result of solvent residue caused by the interfacial tension that exists between the solvent and the substrate. UK Ministry of Defence © Crown Owned Copyright 2020/AWE.

Nitrogen functionalization of MWCNTs in Ar-[formula omitted] dielectric barrier discharge – Gas ratio effect

In this work, the effect Ar-N2 mixture plasma on the surface characters and structure of MWCNTs were investigated. The plasma treatment was performed at various nitrogen gas ratio, while RF power, treatment time and gas pressure were kept fixed. The plasma species were monitored with optical emission spectroscopy. The X-ray photoelectron spectroscopy (XPS) confirmed the formation of nitrogen functional groups on the plasma- treated MWCNTs outer surface and its concentrations are dependent on the nitrogen gas ratio in the mixture plasma. The Raman analysis results are consistent with XPS observation. The MWCNTs surface roughness is enhanced as nitrogen gas ratio is increased in the plasma as observed by TEM and XPS images. The MWCNTs structure was not damaged as observed by XRD pattern. The correlations between the relative intensities of Ar-N2 plasma species and the surface characters of the MWCNTs are also investigated.

Chemical Imaging of Human Fingermark by X-ray Photoelectron Spectroscopy (XPS).

X-ray photoelectron spectroscopy (XPS) is a widely used technique to characterize the surface chemistry of materials. It plays a crucial role in accessing qualitative and quantitative information and in detecting the presence of chemical functional groups on the surface of any material. The forensic methods available to detect and identify elements and organic/inorganic compounds are often destructive, so evidence cannot be re-analyzed. However, XPS allows rapid analysis of samples without damaging them. Recently, an increasing number of forensic researchers have begun to study certain chemical information on fingermarks. In this study, the authors aimed to present the applicability and power of XPS imaging in fingermark analysis which can also provide specific information about the fingermark chemical composition. Herein, monochromated X-ray (Al Kα) spot size was fixed at 50 μm. XPS mapping resulted in the acquisition of spectra at each pixel, in an array of 41 × 30 pixels with a step size of 50 μm. Then, a simple discussion has been made about how the scanned surface spectrum and basic snapshot spectra are used to identify different components at a fingertip of a scanned surface area (~3 mm2 ). Hence, a fingermark pattern contaminated with caffeine, TiO2 , and Pb/PbO deposited on the silicon wafer can be chemically mapped and visualized by XPS using principal component analysis (PCA). Thus, the present study showed the possible applicability of XPS for the identification of illicit drugs of abuse, gunshot residue, and skin care products on latent fingermark by mimicking a crime scene evidence.

Structural Modelling of Hybrid ZnO-CdSe Nano-Compounds Using X-ray Photoelectron Spectroscopy Depth-Profiling Technique.

In the present work, ZnO nanoparticles were synthesized using chemical route method. Composition ratio for Zn:O and various oxidation states were determined using XPS (X-ray photoelectron spectroscopy) technique. The 1 hr calcined ZnO nanoparticles were found to the best due to their monodispersed nature (size ˜20 nm) and high purity. These nanoparticles were then used for synthesizing ZnO-CdSe nano-compounds. These nanocrystals were integrated with CdSe qdots (synthesized using Hot-Injection technique) of varied size (5 nm and 8 nm) via MPA (mercaptopropionic acid) as a linker to develop hybrid nano-compounds for photoactive applications like Quantum Dot sensitized solar cells (QDSSC's) etc. Here, the main objective of the work was to explore the structure of hybrid nano-compounds. XPS-depth-profiling technique was used as an investigation technique for the compositional and structural analyses of ZnO-CdSe nano-compounds. The compositional structure was analyzed layer wise (obtained by etching at different time of sputtering) for the exact position of ZnO and CdSe nanoparticles. On the basis of above study utilizing depth profiling technique of XPS and TEM images, it was found that high quality of hybrid nano-compounds can be synthesized with smaller sized quantum dots, as compared to larger sized quantum dots because of unbounded phosphorus (P) and selenium (Se). Also, it confirms the role of linker that strengthens the binding of CdSe quantum dots on the surface of ZnO thus making it hard to separate the anchored, interstitial CdSe completely which paves the way for the development of stoichiometric, structurally and morphologically-stable ZnO-CdSe nano-compounds.

Neutrophils Activated by Nanoparticles and Formation of Neutrophil Extracellular Traps: Work Function Mapping and Element Specific Imaging.

Photoemission electron microscopy (PEEM) and imaging X-ray photoelectron spectroscopy (XPS) have over the years been powerful tools in classical surface physics and material sciences, and due to recent technological advances, their uses within other fields/disciplines are rapidly growing. Lately, the XPS/PEEM based elemental analysis and characterization in imaging mode, with exquisite spatial resolution and high sensitivity, has shown the potential to deliver new mechanistic insights in cell-biology/medicine. In this work, the aim was to visualize biological processes on the cellular level, with the additional dimension of topographical morphology and element specific information, mapping chemical composition and chemical states. This is hereby demonstrated by combined PEEM and imaging XPS investigation of neutrophils and their activation processes, where fluorescence microscopy commonly used in biology is used for benchmarking. Neutrophils are phagocytic cells and are vital components in the human immune system, with the fundamental role of fighting invading pathogens. They are capable of ingesting microorganisms or particles, and in order to capture and trap foreign objects, one of their strategies is to release nuclear DNA by the formation of extracellular web-like traps (NETs). Here, we report how neutrophils are triggered by controlled nanoparticle (NP) exposure. The neutrophils and NETs formation are imaged in the presence of NPs, and we report the elemental composition of single cells and the structure of NETs. Cellular uptake of nanoparticles is proven and the states just before and after NETs release are imaged, as well as visualization of the extraordinary capability for mass transport at distances 10 times or more than the size of the cell itself. This method paves the way for element specific imaging of biorelated cells on surfaces as well as nanoparticle tracking in the submicro- and nanoregions.

Thermomechanical Polymer Binder Reactivity with Positive Active Materials for Li Metal Polymer and Li-Ion Batteries: An XPS and XPS Imaging Study.

The lithium and lithium-ion battery electrode chemical stability in the pristine state has rarely been considered as a function of the binder choice and the electrode processing. In this work, X-ray photoelectron spectroscopy (XPS) and XPS imaging analyses associated with complementary Mössbauer spectroscopy are used in order to study the chemical stability of two pristine positive electrodes: (i) an extruded LiFePO4-based electrode formulated with different polymer matrices [polyethylene oxide and a polyvinylidene difluoride (PVdF)] and processed at different temperatures (90 and 130 °C, respectively) and (ii) a Li[Ni0.5Mn0.3Co0.2]O2 (NMC)-based electrode processed by tape-casting, followed by a mild or heavy calendering treatment. These analyses have allowed the identification of reactivity mechanisms at the interface of the active material and the polymer in the case of PVdF-based electrodes.

Dynamic Nitroxide Functional Materials.

A substrate-independent and versatile coating platform for (spatially resolved) surface functionalization, based on nitroxide radical coupling (NRC) reactions and the formation of thermo-labile alkoxyamine functional groups, was introduced. Nitroxide-decorated poly(glycidyl methacrylate) (PGMA) microspheres, obtained through bioinspired copolymer surface deposition using dopamine and a nitroxide functional dopamine derivative as monomers, were conjugated with small functional groups in a rewritable process. Reversible coding of the nitroxide functional microspheres by NRC and decoding through thermal alkoxyamine fission were monitored and characterized by electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, this nitroxide coating system was exploited in "grafting-to" polymer surface ligations of poly(methyl methacrylate) (PMMA) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) in spatially confined areas. Polymer strands terminated with an Irgacure 2959 (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone) photoinitiator were obtained through chain-transfer polymerization, and subsequently coupled to nitroxide-immobilized poly(dopamine) (PDA)-coated silicon substrates by using rapid photoclick NRC reactions. Light-driven polymer surface coding was visualized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and XPS imaging.

XPS Analysis and XPS Imaging of the Passivation Film Formed on Metallic Lithium Electrodes Cycled in Different Liquid Organic Electrolytes

The demand for a battery technology that could involve metallic lithium as negative electrode is motivated by the fact that lithium is the lightest and the most electropositive of all metals (E0 =-3.04 Volts) 1. Ddrawbacks of this electrode material are double : first, lithium deposit has a tendency to be dendritic, ending up in short circuiting the battery; secondly, when lithium plates, some electrolyte is co-deposited, resulting in a poor density of the as-deposited metal. This-mossy-like lithium results in a consumption of the electrolyte, leading to a premature death of the battery. Thus, improving the metallic lithium/electrolyte interface quality is important for avoiding the consumption of solvent and/or salt during electrochemical processes. In this context, the understanding of the chemical proprieties of this interface, commonly named SEI (for Solid Electrolyte Interphase), is crucial in order to improve the quality of lithium plating and stripping and to select the adequate electrolyte for a given battery system. A particularly well-adapted method for investigating the SEI layer composition is the use of X-ray Photoelectron Spectroscopy (XPS) analyses. This post-mortem surface analysis technique, increasingly used in battery characterization, gives essential information not only on the active material but also on the phenomena occurring during cycling 2. The purpose of this work is to investigate by XPS the SEI layer thickness and chemical nature, and their influence on the battery electrochemical performance. The study is carried out on lithium electrodes stemming from metallic lithium symmetric cells cycled (by lithium electrodeposition and stripping) in different liquid electrolytes (different salts and solvents). XPS imaging is also used in this work in order to get a chemical mapping of the SEI layer components formed on the metallic lithium electrode surfaces cycled in different conditions. Data processing based on the principal component analysis (PCA) method has been conducted in order to illustrate the SEI layer heterogeneities. The results are compared with energy-dispersive X-ray spectroscopy (EDS) mapping and highlight the XPS imaging benefits and precision to identify chemical compounds distribution. An example for a lithium electrode cycled in the liquid electrolyte (LiTFSI, Polyethylene Glycol (PEG)) is shown in Figure 1, displaying O 1s (Li2CO3) (a), C 1s (Li2CO3) (b), N1s (LiTFSI) (c) and F 1s (LiTFSI) (d) XPS core peaks components mapping and in Figure 2, displaying the EDS fluorine- oxygen (a), sulfur-oxygen (b) and fluorine-sulfur (c) overlapped mappings for the same sample. These results have led to a better knowledge of the redox processes occurring at the top surface of lithium electrodes cycled in different liquid electrolytes. M. Lécuyer, J. Gaubicher, M. Deschamps, B. Lestriez, T. Brousse, D. Guyomard , J. Power Sources, 241, 249–254 (2013)L. Martin, H. Martinez, M. Ulldemolins, B. Pecquenard, and F. Le Cras, Solid State Ionics, 215, 36–44 (2012) Figure 1

Applying XPS to support industrial research and manufacturing

X-ray photoelectron Spectroscopy (XPS) is a widely-used technique for surface chemical analysis. In an industrial laboratory XPS can be used for a wide variety of applications ranging from identification of contamination on a surface to characterization of materials as process control, or as a method for characterizing new materials in a research environment. Some analyses are performed to provide a ‘yes’ or ‘no’ answer to questions such as ‘is silicone present?’ or ‘was the surface plasma treated?’. In other cases, qualitative analysis or a simple approach for quantification does not adequately describe a material. A more detailed analysis may require imaging or depth profiling, and the use of numerical methods such as curve fitting, overlayer modeling, or linear least squares fitting to more accurately describe a material. We relate selected vignettes where XPS spectral analysis, imaging, and sputter profiling are applied to some of the many types of samples that have come into our industrial laboratory.

Application of quantitative X‐ray photoelectron spectroscopy (XPS) imaging: investigation of Ni‐Cr‐Mo alloys exposed to crevice corrosion solution

This paper explores quantitative X‐ray photoelectron spectroscopy imaging on three different Ni‐Cr‐Mo Hastelloy® alloys (BC‐1, C‐22 and G‐30) with differing Cr and Mo contents. The alloys were subjected to a simulated critical crevice corrosion solution. Ni‐based alloys have been shown to exhibit excellent resistance to a range of corrosive media due to the formation of an inert oxide layer, primarily containing Cr and Mo. However, these alloys may rapidly corrode in the crevice environment produced by seams, gaskets or deposits of debris on the alloy surface. Understanding how the oxide film is influenced by the Cr and Mo content is crucial in determining an optimal alloy composition that reduces or suppresses the possibility of crevice corrosion. The protective oxide films are very thin in nature, generally several nanometers. XPS imaging was used to monitor changes in oxide film composition and to correlate the distribution of Cr and Mo to the grain structure of the alloys. Copyright © 2017 John Wiley & Sons, Ltd.