SpectraFit XPS: a free, browser-based application for X-ray photoelectron spectroscopy peak fitting and quantification
SpectraFit XPS is a free, browser-based application that enables secure, client-side X-ray photoelectron spectroscopy (XPS) data analysis, offering advanced peak fitting, quantification, and ISO 14976 file support with verified accuracy against the open-source KherveFitting project.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Surface chemistry is the study of the very thin outer layer of any material, a realm where the atoms behave differently than they do in the bulk of the object. To understand what a material is made of, or how it will react with the world around it, scientists must look at this skin. They use a technique called X-ray photoelectron spectroscopy, which works by shining X-rays onto a sample. These rays knock electrons loose from the atoms inside. By measuring the energy of these flying electrons, researchers can identify exactly which elements are present and how they are bonded to their neighbors. This process is essential for developing new materials, from the coatings on airplane wings to the circuits in a smartphone. However, turning the raw data from these machines into a clear chemical story is difficult. The data comes as a complex curve, and scientists must carefully separate overlapping signals, choose the right mathematical shapes to represent them, and subtract the background noise to reveal the true composition. For decades, this crucial step has required expensive, specialized software that sits on a single computer, creating a barrier for students, teachers, and researchers who need to analyze data quickly or on different machines.
A new tool called SpectraFit XPS removes these barriers by bringing the entire analysis process into a standard web browser. Developed by Yongsup Park at Kyung Hee University in Seoul, this application allows anyone to perform sophisticated chemical analysis without installing any software or sending their data to a server. The program runs entirely on the user's own computer, meaning the sensitive data from a sample never leaves the machine, a feature that is vital for protecting unpublished research or proprietary industrial samples. The application is designed to handle the everyday workflow of a scientist: loading a file, selecting a specific region of the spectrum to study, choosing a background model, and placing peaks to represent different chemical states. It then uses a powerful mathematical engine to fit these shapes to the data, refining the positions and heights of the peaks until they match the measured curve as closely as possible.
The software is built to be as flexible as the desktop programs it rivals, offering a wide range of tools for interpreting the data. It can model the peaks using several different line shapes, including true Voigt profiles that combine two distinct mathematical curves, and asymmetric shapes specifically designed for metals. It also includes advanced methods for handling the background noise, such as dynamic models that adjust automatically as the peaks change. A key feature is its ability to link peaks together; for example, if a scientist knows that two peaks must appear at a specific distance from each other because they come from the same type of atom, the software can lock them together so they move in unison during the analysis. This ensures that the final result respects the known physics of the elements being studied. The tool also supports spin-orbit doublets, which are pairs of peaks that naturally occur for certain elements, allowing the software to generate them automatically based on established rules rather than requiring the user to place them manually.
Once the peaks are fitted, the application moves to quantification, which is the process of calculating how much of each element is present. It does this by taking the area under each fitted peak and comparing it against a database of known sensitivity factors, which account for how easily different elements release electrons. The software can apply corrections for the energy of the electrons and the angle at which they are detected, ensuring the final numbers are accurate. It includes a library of sensitivity factors for various types of X-ray machines, such as those made by Thermo, Kratos, and PHI, and can automatically detect the instrument used from the file header to select the correct settings. In tests, the application has been shown to reproduce the results of established reference software exactly, matching the values in a suite of thirty different test cases with zero deviation. This level of precision gives researchers confidence that the numbers they see on their screen are reliable.
The tool is designed to be accessible to a wide audience, including students and collaborators who may not have access to expensive laboratory software. It reads standard file formats used by almost all X-ray machines, as well as common spreadsheet files, and can export the results as high-quality images ready for publication. The developers have included a synthetic dataset based on a common plastic called poly(ethylene terephthalate), allowing new users to practice fitting and quantification without needing their own data. While the software is powerful, the author is clear about its current limits. The automatic identification of elements in broad scans is still approximate and can miss weak signals or report false positives in complex mixtures. For the most accurate work, the author recommends analyzing the data region by region, where the user can carefully label each peak. The application is free to use, bilingual in English and Korean, and represents a significant step toward making high-level surface analysis available to anyone with a web browser, democratizing a tool that was once restricted to those with specific, costly software licenses.
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