This image shows how XPS can be used to obtain information about chemical states at the material-vacuum interface. The image on the left is a map of a Ta2O5 film on Ta metal. The pattern was generated by rastering a small spot Argon sputter beam over the square area to remove some of the oxide, exposing the metal. The map is generated by the intensity due to tantalum 4f electrons in the metallic state, red indicating stronger intensity, thus more metallic. The spectra on the right were taken at the positions marked on the map as p1, p2 and p3. One can see the transition from metallic tantalum to tantalum oxide as the position of the peaks shifts from the red (metallic) position to the blue (oxide) position, with the coexistence of both metal and oxide shown as the green spectrum.
