PROBING DEPTH OF SOFT-X-RAY ABSORPTION-SPECTROSCOPY MEASURED IN TOTAL-ELECTRON-YIELD MODE

Two series of experiments on well-characterized systems were performed to examine the probing depth of soft x-ray absorption spectroscopy (XAS) measured in total-electron-yield (TEY) mode. First we measured the Ni 2p3/2 absorption spectra of Ni(100) covered with Tb as a function of the overlayer thickness. Secondly we recorded the O 1s absorption spectra of Ta2O5 films produced by controlled anodic oxidation of Ta foils as a function of the oxide thickness. The mean probing depth (MPD) was found to be much shorter than previously assumed (for O 1s, only 1.9 nm). The relative importance of those cascade mechanisms that lead to the electron current measured in TEY is discussed.