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X‐ray photoelectron spectroscopy (XPS) is the most widely used and important method for chemically analyzing and speciating surfaces. XPS has surface sensitivity (5–10 nm), is quantitative, and is able to probe the oxidation states of the elements at surfaces. However, during the past few years, a great deal of incorrect XPS data analysis has entered the scientific literature. Accordingly, efforts, including this Insight Note, are being made to provide tutorial information to the scientific community. Aluminum is a scientifically and technologically important element. Here we discuss approaches for fitting the Al 2p peak envelope from a sample of aluminum foil with a thin layer of oxide on it. Signals from the metal and oxide are present. We discuss methods for electrically isolating (or not isolating) the sample during data acquisition, the choice of the baseline, fitting the oxide peak with one or two synthetic peaks, and fitting the metal signal with two symmetric or two asymmetric peaks. The thickness of the oxide is calculated based on the areas of the oxide and metal signals. [ABSTRACT FROM AUTHOR]

This study was motivated by earlier observations. It is a systematic examination of the adequacy of reporting of information (metadata) necessary to understand x-ray photoelectron spectroscopy (XPS) data collection and data analysis in the scientific literature. The information for this study was obtained from papers published in three high-quality journals over a six-month period in 2019 and throughout 2021. Each paper was evaluated to determine whether the authors had reported (percentages of the papers properly providing the information are given in parentheses) the spectrometer (66%), fitting software (15%), x-ray source (40%), pass energy (10%), spot size (5%), synthetic peak shapes in fits (10%), backgrounds in fits (10%), whether the XPS data are shown in the main body of the paper or in the supporting information (or both), and whether fitted or unfitted spectra were shown (80% of published spectra are fit). The Shirley background is the most widely used background in XPS peak fitting. The Al Kα source is the most widely used x-ray source for XPS data collection. casaxps is the most widely used fitting program for XPS data analysis. There is good agreement between the results gathered during the two years of our survey. There are some hints the situation may be improving. This study also provides a list of the information/parameters that should be reported when XPS is performed. [ABSTRACT FROM AUTHOR]

Due to significant advances in instrumentation, many previously specialized techniques have become "routine" in user facilities. However, detailed knowledge held by experts has often not been relayed to general users, so they often rely on entry-level information, basic principles, and comparison with literature results for data analysis. As a result, major errors in the data analysis of multiple surface and material analysis techniques, including in x-ray photoelectron spectroscopy (XPS), have been appearing in the scientific literature. Representative examples of serious errors in XPS data analysis are shown in this work. We suggest that surface and material analysis, and perhaps even science in general, are in a state of "pre-crisis." We use two (logistic) models from population biology to suggest that bad analyses self-correct if they remain below a critical number. However, beyond a threshold, the literature can become useless because of the perpetuation of faulty analyses and concomitant loss of its self-correcting ability. XPS is used by scientists in many communities because of the power of the technique and high-quality instrumentation that is commercially available. Those who make new surfaces and materials face unique challenges because of the large number of surface and material analytical techniques that are often needed to characterize their materials. Graduate students and post-docs are often provided with only minimal instruction on using surface and material characterization methods. High fees for instruments may affect both the quality and the quantity of the data people collect. The Prisoner's Dilemma is a model from game theory that describes situations with reward structures that encourage uncooperative behavior and lead to suboptimal outcomes. However, the outcomes of Prisoner's Dilemma are not inevitable—their consequences change if their reward structures change. The current system does not appear to incentivize detailed learning of surface and material characterization techniques and careful material characterization. Prisoner's dilemmas appear to lead to other undesirable consequences in science. The concerns raised in this work suggest that many manuscripts are incompletely reviewed at present. The different stakeholders in this problem, including authors, research advisers, subject matter experts, reviewers, scientists who notice examples of faulty data analysis, editors, journals and publishers, funding agencies, scientific societies, leaders at universities and research centers, and instrument vendors, can improve the current situation. This work provides specific recommendations for each of these stakeholders. For example, we believe that authors are primarily responsible for the correctness of their work, not reviewers or editors; we question the wisdom of listing the names of the editor and reviewers on a paper; we are grateful for the significant contributions that have been made by subject matter experts to produce standards and tutorial information; the high cost of instrument time at some institutions may limit student access and result in suboptimal analyses; staff scientists often need to be better recognized for their intellectual contributions to studies; publishers may wish to allow selective reviewing of specific sections of papers related to material characterization; the reviewing at some open access journals may be inadequate; while it had its shortcomings, the pre-open access model of publishing incentivized the production and publication of high-quality work; audits of the products (scientific papers) of funding agencies may be necessary; collaboration needs to be encouraged to a greater extent at some institutions; and instrument vendors should not suggest to potential customers that surface characterization, e.g., by XPS, is trivial or simple. [ABSTRACT FROM AUTHOR]

The carbon 1s photoelectron spectrum is the most widely fit and analyzed narrow scan in the x-ray photoelectron spectroscopy (XPS) literature. It is, therefore, critically important to adopt well-established protocols based on best practices for its analysis, since results of these efforts affect research outcomes in a wide range of different application areas across materials science. Unfortunately, much XPS peak fitting in the scientific literature is inaccurate. In this guide, we describe and explain the most common problems associated with C 1s narrow scan analysis in the XPS literature. We then provide an overview of rules, principles, and considerations that, taken together, should guide the approach to the analysis of C 1s spectra. We propose that following this approach should result in (1) the avoidance of common problems and (2) the extraction of reliable, reproducible, and meaningful information from experimental data. [ABSTRACT FROM AUTHOR]

This study was undertaken to understand the extent and nature of problems in x-ray photoelectron spectroscopy (XPS) data reported in the literature. It first presents an assessment of the XPS data in three high-quality journals over a six-month period. This analysis of 409 publications showing XPS spectra provides insight into how XPS is being used, identifies the common mistakes or errors in XPS analysis, and reveals which elements are most commonly analyzed. More than 65% of the 409 papers showed fitting of XP spectra. An ad hoc group (herein identified as "the committee") of experienced XPS analysts reviewed these spectra and found that peak fitting was a common source of significant errors. The papers were ranked based on the perceived seriousness of the errors, which ranged from minor to major. Major errors, which, in the opinion of the ad hoc committee, can render the interpretation of the data meaningless, occurred when fitting protocols ignored underlying physics and chemistry or contained major errors in the analysis. Consistent with other materials analysis data, ca. 30% of the XPS data or analysis was identified as having major errors. Out of the publications with fitted spectra, ca. 40% had major errors. The most common elements analyzed by XPS in the papers sampled and researched at an online database, include carbon, oxygen, nitrogen, sulfur, and titanium. A scrutiny of the papers showing carbon and oxygen XPS spectra revealed the classes of materials being studied and the extent of problems in these analyses. As might be expected, C 1s and O 1s analyses are most often performed on sp2-type materials and inorganic oxides, respectively. These findings have helped focus a series of XPS guides and tutorials that deal with common analysis issues. The extent of problematic data is larger than the authors had expected. Quantification of the problem, examination of some of the common problem areas, and the development of targeted guides and tutorials may provide both the motivation and resources that enable the community to improve the overall quality and reliability of XPS analysis reported in the literature. [ABSTRACT FROM AUTHOR]

• The Ho and McKay equation makes the impossible prediction of infinite adsorption. • The flaw in the Ho and McKay equation is in its half-stable fixed point. • A straightforward mathematical fix for the Ho and McKay equation is presented. Ho and McKay's pseudo-second order equation is widely used for fitting adsorption data, often outperforming Lagergren's model. However, the Ho and McKay equation contains a mathematical inconsistency that predicts infinite adsorption for q > q e. This issue should be resolved. This problem is illustrated graphically using the mathematical concept of 'flow along the line'. This analysis reveals that the problem with the Ho and McKay model is its half-stable fixed point. Other variants of the Ho and McKay equation similarly predict infinite adsorption for q > q e. In contrast, the Lagergren equation does not show this anomaly – it has a stable fixed point. An analysis of more than 250 papers in the scientific literature that cite the Ho and McKay equation confirms that real adsorption experiments do not follow the predictions of the Ho and McKay equation for q > q e ; they do not show 'runaway' behavior. That is, the issue raised in this work is purely mathematical/theoretical; it is about following recommended practices for making precise models. A simple solution to the inconsistency in the Ho and McKay equation is to only define it for q ≤ q e. Other possible fixes for this equation are also discussed. [ABSTRACT FROM AUTHOR]