XPS measurements for probing dynamics of charging
The technique of recording X-ray photoemission data while the sample rod is subjected to ±10.0 V (dc) or square-wave pulses (ac) with varying frequencies in the range of 10-3 to 103 Hz for probing charging/discharging dynamics of dielectric materials, is reviewed. Application of this technique introduces charging shifts as well as broadening of the peaks, which depend non-linearly on the polarity, as well as on the frequency of the pulses applied. These changes have been measured on: (i) an artificially created dielectric sample consisting of a Au metal strip connected externally to a series resistor of 1 MΩ and a parallel capacitor of 56 nF, and two real dielectric films; (ii) a 20 nm organic polystyrene film spin-coated on a silicon substrate; (iii) a 10 nm SiO2 inorganic layer thermally grown on silicon. A simple circuit model is introduced to simulate the charging shifts and the peak broadenings. Although this simple model faithfully reproduces the charging shifts in all three cases, and also some of the broadenings for the artificial dielectric and the polystyrene film, the additional broadening in the negatively charged peaks of the SiO2 dielectric film cannot be accounted for. It is also claimed that these experimental findings can be used for extracting material-specific dielectric properties.