Advantages of soft X-ray absorption over TEM-EELS for solid carbon studies--a comparative study on diesel soot with EELS and NEXAFS

Diesel soot was investigated with electron energy loss spectroscopy (EELS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The EELS spectra were obtained in connection with transmission electron microscopy studies, whereas the NEXAFS were obtained from a scanning transmission X-ray microscope (STXM) and from a conventional NEXAFS beamline at two synchrotron facilities. The X-ray absorption spectra show molecular species, aliphatics, such as carboxyl, and C-H bonds, which are not visible in EELS spectra of the same material. In particular, EELS fails to detect surface-functional groups, which can be detected with NEXAFS. Since numerous works on molecular carbon structure determined with TEM-EELS have been published, it is possible that these results have to be reassessed.