X-ray photoemission spectroscopy of film stoichiometry and valence state
(Color online) XPS core level spectra from standard samples of (a) and (b) . The XPS system’s sensitivity to Fe relative to O, , was determined from and the system’s sensitivity to Sr and Mo relative to O, and , was determined from .
(Color online) (a) Oxygen and strontium composition vs sputter time. (b) Iron and molybdenum concentration vs sputter time. The oxygen content is seen to drop with longer sputter times indicating preferential removal. As a result, the iron, strontium, and molybdenum contents increase.
(Color online) Fe/Mo composition vs sputter time. The Fe/Mo ratios for XPS and RBS agree after 30 s sputter time.
(Color online) Fe region vs sputter time. The valence state of iron can be determined from the Fe satellite peak position and by deconvolving the main emission line.
(Color online) Mo region vs sputter time. At 0 s the Mo emission is dominated by the presence of a overlayer. As the overlayer is removed, the Mo emission features can be assigned to and . Lattice damage is evident with the appearance of metallic at 120 s.
Core level peaks areas from XPS measurements of standard samples (Fig. 1) used to calculate the XPS sensitivity from Eq. (1) and the known atomic concentrations of the stoichiometric standards. Sensitivity factors relative to oxygen are also shown.
Atomic sensitivity factors obtained on the basis of three sources: the Handbook of X-ray Photoelectron Spectroscopy (Ref. 8), XPS measurements of standard samples of and , and XPS measurements of SFMO with Sr, Fe, and Mo compositions known from RBS. The sensitivity factors obtained from the standard samples were used as a starting point and then self-consistently adjusted to yield the relative amounts of Sr, Mo, and Fe determined by RBS while maintaining oxygen stoichiometries of the standard samples.
Comparison table of SFMO bulk film composition from XPS (atomic %) vs RBS (relative compositions of Sr, Fe, and Mo). Due to RBS’s lack of sensitivity to oxygen, a column showing the Fe:Mo ratio is also included showing good agreement between XPS and RBS measurements.
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