AUTHOR=Baer D. R. , Sherwood P. M. A. TITLE=Perspective on the development of XPS and the pioneers who made it possible JOURNAL=Frontiers in Analytical Science VOLUME=4 YEAR=2025 URL=https://www.frontiersin.org/journals/analytical-science/articles/10.3389/frans.2024.1509438 DOI=10.3389/frans.2024.1509438 ISSN=2673-9283