Evolving efforts to maintain and improve XPS analysis quality in an era of increasingly diverse uses and users

Based on literature analysis, X‐ray photoelectron spectroscopy (XPS) use continues to increase exponentially. This increased use is accompanied by anecdotal reports and systematic analyses indicating a growing presence of significantly flawed data analyses. Recognition of this problem within the surface analysis community has increased with an understanding that both inexperienced users and increased use of XPS outside the surface analysis community contribute to the problem. The XPS community has initiated several efforts to help address the problem, which is not unique to XPS. This paper describes some of the specific problems identified and some of the community efforts intended to address them. Here, we describe activities focused on three specific issues: (i) requests for detailed guides and protocols and bite‐sized versions of information for non‐experts, (ii) incomplete data and analysis reporting, and (iii) the high rate of peak fitting problems. A 2019 survey identified the need for guides, protocols, and standards to assist XPS users. One set of such guides has been published, and another is being assembled. Providing incremental bites of useful information is the goal of a series of papers on specific challenges to surface analysis with example solutions has been initiated as Notes and Insights papers in Surface and Interface Analysis. Examination of XPS‐containing papers finds that information to establish the credibility and reproducibility of XPS results is often very incomplete. Unfortunately, ISO and ASTM standards require an amount of parameter reporting that seems excessive and unrealistic for many research publications. Initial approaches to develop and distribute a graded approach to parameter reporting are briefly described. Multiple efforts are underway to address the high rate of problems associated with photoelectron peak fitting. These include guides to peak fitting, guides to peak identification and fitting for specific elements, and the development of a peak fitting social network. The fitting social network is designed to facilitate interactions between new and experienced XPS users; analysts trying to fit XPS data (for publication or other reasons) can ask questions and establish dynamic conversations. Encouraging and enabling high‐quality XPS analysis and reporting requires several different types of effort from all members of the surface and interface analysis community.

Based on literature analysis, X-ray photoelectron spectroscopy (XPS) use continues to increase exponentially. This increased use is accompanied by anecdotal reports and systematic analyses indicating a growing presence of significantly flawed data analyses. Recognition of this problem within the surface analysis community has increased with an understanding that both inexperienced users and increased use of XPS outside the surface analysis community contribute to the problem. The XPS community has initiated several efforts to help address the problem, which is not unique to XPS. This paper describes some of the specific problems identified and some of the community efforts intended to address them. Here, we describe activities focused on three specific issues: (i) requests for detailed guides and protocols and bite-sized versions of information for non-experts, (ii) incomplete data and analysis reporting, and (iii) the high rate of peak fitting problems. A 2019 survey identified the need for guides, protocols, and standards to assist XPS users. One set of such guides has been published, and another is being assembled. Providing incremental bites of useful information is the goal of a series of papers on specific challenges to surface analysis with example solutions has been initiated as Notes and Insights papers in Surface and Interface Analysis. Examination of XPS-containing papers finds that information to establish the credibility and reproducibility of XPS results is often very incomplete.
Unfortunately, ISO and ASTM standards require an amount of parameter reporting that seems excessive and unrealistic for many research publications. Initial approaches to develop and distribute a graded approach to parameter reporting are briefly described. Multiple efforts are underway to address the high rate of problems associated with photoelectron peak fitting. These include guides to peak fitting, guides to peak identification and fitting for specific elements, and the development of a peak fitting social network. The fitting social network is designed to facilitate interactions between new and experienced XPS users; analysts trying to fit XPS data (for publication or other reasons) can ask questions and establish dynamic conversations. Encouraging and enabling high-quality XPS analysis and reporting requires several different types of effort from all members of the surface and interface analysis community.

| INTRODUCTION
Over the past two decades, the use of X-ray photoelectron spectroscopy (XPS) has grown so that it is the most widely used surface analysis method, important in many areas of science and technology. A side effect of this expanded use has been the observations of a growing number of publications containing faulty XPS data and, more often, data analysis. The causes of this problem are many but include a new generation of XPS users and the increasing importance and use of XPS outside of the surface and interface analysis community. This publication notes some of the recent and evolving efforts intended to address the issue and assist non-traditional and newer XPS users in producing and reporting quality XPS results.
The exponential growth of the use and importance of XPS 1 ( Figure 1) is built upon the development of highly reliable and stable instrumentation that has overcome challenges identified decades ago. 2,3 Important application areas include studies of catalysts, energy materials, corrosion, polymers, biomaterials, nanotechnology, and recently expanding to include additional materials and systems of biological and environmental importance. Instrumental advances involving the use of new higher energy X-ray sources enabling analysis of layers deeper into materials than standard XPS (HAXPES) 4 and differentially pumped systems enabling measurements at pressures higher than available for traditional systems (near ambient pressure XPS, NAP-XPS) 5 have further extended the use of XPS to address important scientific challenges. Along with this growing use, experienced XPS analysts have become concerned by an increase of inappropriately collected, analyzed, or reported data. Because of these anecdotal observations of problematic XPS data in journal publications, a systematic study was undertaken. This study examined 6 months of XPS data in three journals. 6 The conclusions are startling ( Figure 2). On average over the three journals, 30% of the papers contained major flaws (red) making conclusions from the XPS data invalid, and an additional 30% (orange) had significant problems that may or may not have made the conclusion invalid. Only 40% of the data were classified as having minor or no issues (yellow or green). Such observations are not unique to XPS but observed for other analysis methods and areas of science with problematic data between 20% and 30% of the time. 7 Faulty data and analysis slow scientific progress and the benefits it can have for society and the many problems we face. 8  F I G U R E 2 Bar graph showing percentages of papers with highly faulty data (red), data with significant flaws (orange), and data with minor (yellow) or with no apparent concerns (green) based on analysis of 6 months of data from three journals. F I G U R E 3 Elements required for changing a research culture to enhance data reliability. Inspired by a presentation during a Community Dialog on Catalysis Rigor and Reproducibility April 2022, https://www.catalysisrr.org/, by Prof. Jennifer Tackett.
considering general efforts required to enhance the quality and credibility of several areas of science, Tackett 9 observed that this involves a culture change in parts of the scientific community. Such changes require efforts at multiple levels as indicated in Figure 3. Activities and developments of different types are needed to change the culture. The community must have the knowledge and infrastructure that enables high quality science, useful tools and access to that knowledge must be easy to find and apply, and the community must have expectations that they will be used with some types of rewards for using them. If all of these are in place, a policy to require to their use might be possible and/or appropriate. As can be seen, efforts at multiple levels involving many aspects of the scientific community will be required to address the issues for XPS and other analysis methods.
Such activities will involve analysts, researchers, reviewers, journal editors, research institutions, professional societies, and funding agencies.
As noted above, most of the instrumental issues identified decades ago have been addressed, and data quality is usually quite good. Although there can be sample preparation, data collection, and damage issues, many of the current problems are associated with faulty data analysis and reporting. In this paper, we summarize four efforts to assist XPS users in producing quality XPS analysis, including the motivation for each and the specific aspects of the problem they are trying to address. These include journal publications of guides to the use of XPS, short papers examining specific surface analysis issues, assisting instrument parameter and analysis reporting, and a webbased effort to help with the challenges associated with peak fitting.
2 | CHALLENGES AND EFFORTS TO ADDRESS THEM

| Guides and protocols
A 2016 publication in Nature involving a survey of more than 1500 scientists found that 90% indicated that there were problems with reproducibility in many areas of science and 50% indicated that it was serious. 10  challenges. Consistent with other such surveys, a significant percentage of those responding (65%) found it to be a significant problem. 11 Challenges appeared within an individual's research, within a research team, and most significantly in results reported in the literature. Making the issue visible and providing useful information, such as protocols, checklists, guides, and standards, were identified as ways to help address the challenge. areas of XPS were discussed such as curve fitting, 12 quantification, 13 and sample charging. 14 Based on this success, but recognition that there are additional topics relevant to XPS and needs for other surface analysis methods, a second collection will be published that expands into other areas of surface analysis.
The second reproducibility special topic collection will include issues related to Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), low-energy ion scattering spectroscopy (LEIS), ellipsometry, and scanning probe methods (SPM), as well as XPS topics not fully covered in the first collection. The intent is to include papers that identify important challenges faced by analysts that often lead to incomplete or erroneous results and to identify useful protocols and other solutions. 15 Papers are also encouraged that address issues and opportunities raised by the introduction of new technologies and modern analysis methods including machine learning (ML) and artificial intelligence (AI).
Papers may focus on specific techniques or application areas, data collection and/or analysis, or appropriate reporting for reliable and reproducible data and analysis. Examples of research approaches, establishing expectations, protocols, workflows, method validation, checklists, and other efforts to address reproducibility issues are encouraged.
The call for papers indicates that the topics to be covered include, but are not limited to, reproducibility challenges and solutions related to: It is also important to acknowledge and recognize that because many XPS analysts are concerned about these issues, other efforts in addition to those described here have been or are being prepared.
Examples include a step-by-step guide to perform XPS, 16 a paper on the systematic and collaborative approach to problem solving using XPS, 17 and the XPS Library. 18 2.1.2 | Addressing specific surface analysis challenges: Surface analysis notes and insights Although the paper collection described above has been well received and found useful by many members of the research community, some have expressed concern that these guides cover too many topics and are not helpful to researchers looking for specific rapid answers to their questions and analysis needs. As an effort to provide focused topic shorter papers addressing topics important to non-expert analysts, Surface and Interface Analysis has introduced a new type of paper identified as Notes and Insights. The announcement for these papers was first made at ECASIA 2022 as described below. 19 Introducing a New Type of Short Papers in Surface and

Notes and Insights
Description -Surface and Interface Analysis focused Notes and Insights are intended to be short papers of around one to three pages each, sharing analyst's experiences, helping others to obtain useful surface analysis information from specific materials or sample types.
The Notes allow analysts to share their experience of challenges faced and their solutions. Many researchers have developed tricks to address analysis issues. These are often not easily found and are therefore not available and readably useful to the community using surface analysis methods.
Motivation -As surface analysis methods including XPS and SIMS are increasingly used by those outside the normal surface analysis community, many published papers, especially outside surface focused journals, include faulty data or inappropriate data analysis.
Detailed analysis of XPS data in several publications suggests that more than half of the data and analyses submitted for publication have significant flaws.
Although there are many sources of essential information including guides, standards, and reviews, these are often too long or detailed for the non-expert to find the information important to them. These shorter specific topic descriptions of analysis issues and challenges with example solutions are intended to address specific topics for specific materials or materials systems, and therefore to make useful information readily available to the growing analysis community.
By facilitating the publication of these short, focused topic papers, it will be easier for experienced analysts and researchers to share their knowledge, and it will be easier for general users to find information. The objective is to maintain and improve the quality of the surface information reported in the literature.
Possible Topics -The range of possible topics is as large as the types of issues that analysts have addressed in their efforts to obtain information from surfaces and interfaces. These might include (but are not limited to) sample preparation and mounting, storage and handling, tricks and issues in data collection, pitfalls for specific types of samples, dealing with specimen damage, peak identification or fitting, quantification issues, instrumentation, or software tricks.
Review Process -As for all articles submitted to SIA, Notes and Insights manuscripts will be reviewed before publication. However, the review process will focus on usefulness to analysts rather than requiring innovative novel research. To assist this effort a submission category of Notes and Insights has been added to the SIA submission paper.   Table 1 shows some of the data that was reported for both instrument related information and parameters and information relative to peak fitting. Even basic information such as the nature of the instrument used was not reported 100% of the time, and other important information was reported much less often. Peak fitting, which has been identified as a major problem area, is frequently badly reported.

| Facilitating instrument, data, and analysis reporting
A short summary of her findings includes an observation that the ISO and ASTM standards produced by ASTM E42 and ISO TC201 require what seems to be an unreasonable amount of information to be reported for most journal publications and that such requirements are not being followed. However, published papers were very often not providing nearly enough information to evaluate the credibility of the measurements let alone enough information to enable the data to be replicated or reproduced. There are two interrelated issues and potential benefits improving parameter reporting. First, providing researchers information about which data collection and analysis parameters are important for the credibility of their results will have the benefit of encouraging such information to be followed and recorded. Recognition and recording of the important parameters will improve both the quality of research and make important information available to be included in published work.

| Instrument parameter information
In analyzing the reporting completeness with respect to instrumentation, Gaskell recognized that some of the important information T A B L E 1 Summary of instrument and fitting parameter reporting. Published information about these families of instruments including operation modes and general instrument properties could apply to a significant number of instruments and assist users around the world.
There is now an effort to develop appropriate instrument summary reports for publication in the journal Surface Science Spectra (SSS). Several instrument vendors have agreed to prepare such manuscripts.
The specific content for these papers in being developed, but the ideas for the content and scope of these articles are described below.

Thoughts on Content
Description: Publications in SSS that describe characteristics of a specific family of commercial instrumentation that contain useful instrumental details that authors can reference as they prepare papers using such instrumentation. Such papers should contain a general instrument description, information related to specific operation modes, and identification (and impact) of instrument parameters that are operator selected. Authors preparing a manuscript would need to indicate the instrument (paper reference) along with the operation mode and relevant parameters used.
As noted above, there are efforts to encourage the creation of digital object indicators (DOIs) for specific instruments that might contain the information envisioned in these SSS articles. However, it seems unlikely that most institutions would create such DOIs for the many XPS and other instruments around the world soon. The SSS articles will offer a way for analysts to provide a description of the instruments they used in a publication or report without the need to create a DOI. The collection of instrument information and data provided in SSS articles will also make readily accessible information that can be a challenge for some analysts to provide. Important questions include how such guidance might be best developed and distributed. We note that there is a community initiative in the catalysis community for Robust and Reproducible data that has held a multiday workshop to identify parameters that need to be reported. The editorial team for Applied Surface Science is considering establishing some XPS reporting guidelines that would apply to

| Guidance for general parameter reporting
Applied Surface Science and might be accepted by other journals and the community. The ISO and ASTM standards process can be used to develop an appropriate consensus document, which has community involvement and a regular review process, but these standards are not freely available. Each of the processes has advantages and limitations.
Determining a good approach is an evolving effort, and suggestions are welcome.

| Help for peak fitting
The systematic analysis of XPS data in three journals found that fitting of XPS photoelectron peaks was the source of a high percentage of problems with the published XPS data and analysis. 6  An example of a user proposed fit in comparison with one provided by another user is shown in Figure 5. By comparing approaches and the information that can be obtained, an analyst can increase the confidence they have in their data analysis and have a round or more of feedback on their fit before submission for publication.
As for many social networks, XPSOasis becoming a moderator (with enough Spicer points, a user may become a moderator of a specific forum).

| SUMMARY AND CONCLUSIONS
Because of the value and increasing importance of the information it can provide, the growth in use of XPS, based upon analysis of the literature, has continued at an exponential rate for more than two decades. However, both informal observations and systematic analysis indicate that there is a significant amount of faulty XPS data and F I G U R E 5 Screen shot of an example of a spectrum fit with a comment from another XPSOasis user.
analysis published in many journals. Faulty data analysis has a negative impact on research progress and the benefits that can be provided to society.
Problems with data and analysis have been identified in many areas and are therefore not unique to the surface analysis community or the use of XPS. Correcting this problem involves many levels of effort and has been described as a culture change.
Each member of the surface analysis community has roles to play in maintaining and improving the quality of data in the literature.
The efforts described in this paper are ongoing, and these, and other activities, need active participation of the surface analysis community. Such activities include:

ACKNOWLEDGMENTS
It is appropriate to acknowledge the significant efforts and contributions of the surface analysis community, including individual researchers and analysts, research groups, vendors, standards committees, journal editors, and professional societies, to the efforts described here and to others being undertaken to address data quality and reproducibility issues.

DATA AVAILABILITY STATEMENT
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.