2 It is useful to remember that the XPS information depth is dependent on the energy of the photoelectron and material, but nominally considered to be about 10 nm. As one example, breakdown products of polytetrafluoroethylene (PTFE) were identified on the surface of Cu-oxide nanoparticles as a consequence of the nature of the synthesis process. Qualitative information- What are the particles made of and what is on their surface? Is there unexpected contamination? Do elements on the surface have the expected chemical state? These questions are qualitative and sometimes depend only on the presence or absence of detectable visible signals.
