Is PEXAFS really PhD?

Scanned-energy mode photoelectron diffraction (PhD) measurements from the disordered chemisorption phase formed by oxygen on Cu(111), over a wide range of emission directions, are compared with published surface extended X-ray absorption fine structure (EXAFS) data from the same system. The results show that so-called photoemission EXAFS (‘PEXAFS’) data, even when measured over a wide angular acceptance from a disordered surface, do not reflect the true EXAFS spectrum but are actually dominated by photoelectron diffraction. Quantitative analysis of these data leads to the conclusion that there are likely to be serious systematic errors in all previous PEXAFS analyses.