  We investigate the effect of post-deposition annealing (for temperatures from
848 K to 1273 K) on the chemical properties of crystalline Ta$_2$O$_5$ films
grown on Si(100) substrates by radio frequency magnetron sputtering. The atomic
arrangement, as determined by X-ray diffraction, is predominately hexagonal
($\delta$-Ta$_2$O$_5$) for the films exposed to heat treatments at 948 K and
1048 K; orthorhombic ($\beta$-Ta$_2$O$_5$) for samples annealed at 1148 K and
1273 K; and amorphous for samples annealed at temperatures below 948 K. X-ray
photoelectron spectroscopy for Ta $4f$ and O $1s$ core-levels were performed to
evaluate the chemical properties of all films as a function of annealing
temperature. Upon analysis, it is observed the Ta $4f$ spectrum characteristic
of Ta in Ta$^{5+}$ and the formation of Ta-oxide phases with oxidation states
Ta$^{1+}$, Ta$^{2+}$, Ta$^{3+}$, and Ta$^{4+}$. The study reveals that the
increase in annealing temperature increases the percentage of the state
Ta$^{5+}$ and the reduction of the others indicating that higher temperatures
are more desirable to produce Ta$_2$O$_5$, however, there seems to be an
optimal annealing temperature that maximizes the O\% to Ta\% ratio. We found
that at 1273 K the ratio slightly reduces suggesting oxygen depletion.
