X-Ray Photoelectron Spectroscopy

XPS depth profiling analyzes the composition and properties of a material from the surface down to the interior of the sample, detecting interfaces or changes in the bulk. This is done by first analyzing the sample surface with XPS, and then removing the analyzed material. The newly exposed sample area is then  analyzed, and the process is repeated. The data collected at each level is processed and combined into a compositional plot that shows how the sample changes with increasing depth. XPS depth profiling reveals how materials behave under different conditions, and these insights can help optimize material performance for various applications.

Traditionally, material removal in XPS instruments is performed by either a monoatomic or gas cluster ion beam. Both of these have their limitations, however, and can potentially cause issues such as preferential sputtering or other chemical and structural changes, which can distort results for sensitive samples.

Femtosecond laser ablation (fs-LA) utilizes ultrafast laser pulses to remove material from a sample surface while minimizing the processes that cause chemical damage to the remaining material. This enables precise and controlled removal of material layers, helping to ensure that data collection is representative of the material’s composition. This also makes experiments much faster compared to ion sputtering, so that deeper measurements are more practical to obtain. fs-LA XPS provides highly accurate and detailed analysis for a wide range of materials, making it a powerful tool for surface analysis.

The Hypulse Surface Analysis System features multiple analytical techniques in addition to XPS, including reflected electron energy loss spectroscopy (REELS) and ion scattering spectroscopy (ISS), as well as optional UV photoelectron spectroscopy (UPS). Furthermore, a tilting sample holder can be added for angle-resolved XPS (ARXPS) studies, which are useful for the investigation of certain samples, such as ultra-thin films. Overall, this multi-technique capability provides comprehensive insights into the surface chemistry and structure of a wide variety of materials.

A number of complex materials, from metallurgical and solar-cell samples to polymers, have been analyzed with the damage-free, high-resolution depth profiling of fs-LA XPS.  Specifically, our Hypulse Surface Analysis System brochure highlights several real-world examples, showing how the instrument has been used to analyze nitrided, PVD-coated steels, perovskite solar cells, and multi-layered paint samples.