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XPS spectra of (a) Hf and (b) Si core levels of the system as a function of the deposition time (thickness). The equivalent film thicknesses are about 2, 5, 8, 11, 14, and for deposition times of 1, 2, 3, 4, 5, and . No additional oxygen was supplied during the PLD growth. The shift of the Hf main peak is shown with a guideline, which reflects the transition from Hf silicate to oxygen-deficient .
XPS O spectra of the system prepared under two conditions: (a) no additional supply of oxygen and (b) oxygen supply at a partial pressure of . Each spectrum is fitted by two Voigt functions that correspond to the Hf–O bond and Si–O bond. The intensity ratio is shown at the upper-right corner of each spectra. Si spectra for the same oxygen pressure are shown in the inset of (b).
Si chemical shift relative to is plotted as a function of the intensity ratio of obtained from Fig. 2. (Here a positive value indicates a lower BE.) The overall footprints are found to depend on the oxygen environment, which means that the oxygen vacancy is an important parameter that determines the chemical states.
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