Guide to XPS data analysis: Applying appropriate constraints to synthetic peaks in XPS peak fitting

Peak fitting of x-ray photoelectron spectroscopy (XPS) data is the primary method for identifying and quantifying chemical states atoms near surface a sample. typically based on minimization figure-of-merit, such as residual standard deviation (RSD). Here, we show that optimal XPS peak obtained when shape (the synthetic mathematical function represents material) best matches physics chemistry underlying data. However, because this ideal often unknown, constraints components fit are usually necessary to obtain good fits These may include fixing relative full width at half maxima (peak widths), area ratios, and/or positions components. As shown in multiple examples, while unconstrained, less-than-optimal shapes produce lower RSDs, they lead incorrect results. Thus, “suboptimal” results (somewhat higher RSDs) applied less-than-perfect preferable prevent from yielding unphysical or unchemical performed all information available about sample used, including its expected physical composition, other narrow survey scans same material, analytical techniques.