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Testing Errors in XPS
- Authors
- Name
- Universal Lab
- @universallab
During X-ray photoelectron spectroscopy (XPS) testing, staff at the Universallab Testing Platform discovered through communication with many clients that while many are familiar with XPS from literature, they are still beginners when it comes to understanding its principles. In response, the Universallab team organized colleagues to compile a vast amount of online knowledge, hoping to assist peers in the research community.
XPS detection signals come from the surface of the sample, within a few nanometers of depth. The XPS signal originates from a millimeter-scale region of the sample's surface, including the nanoparticles, the substrate silicon wafer, and impurities on the wafer. XPS is surface-sensitive, so any surface contamination, such as residual ions, can have a significant impact on the results.
Apart from the issue of semi-quantitative accuracy, there are two key differences between XPS and SEM-EDS that need attention:
(1) XPS signals come from the sample's surface, within a few nanometers of depth, while SEM-EDS signals come from a depth ranging from hundreds of nanometers to micrometers. For nanoparticles, this depth typically encompasses the entire particle.
(2) XPS signals originate from the surface area of the sample at the nanometer scale, including the nanoparticles, the substrate, and impurities on the substrate. SEM-EDS signals come from the surface area at the micron or even nanometer scale, with point analysis generally focusing on a single nanoparticle or its aggregates. The substrate’s signal is weaker, and impurities or poorly formed particles on the substrate may be unintentionally ignored.
XPS is highly sensitive to surface contamination, which can significantly affect the results. While XPS is semi-quantitative, EDS is not quantitative. Even with calibration using standard samples, EDS can have errors exceeding 5%, making it unsuitable for precise quantification. ICP can confirm overall element distribution. Additionally, for very small particles, scanning electron spectroscopy is strongly discouraged as the substrate signal is very strong and can create significant interference. In this case, transmission electron spectroscopy (TEM) is recommended. Both XPS and EDS are semi-quantitative and primarily qualitative, with XPS focusing on surface elements within a few nanometers. For accurate quantitative results, ICP is the most reliable method.