  We investigated the dielectric functions $\epsilon$($\omega$) of Ir, Ru, Pt,
and IrO$_2$, which are commonly used as electrodes in ferroelectric thin film
applications. In particular, we investigated the contributions from bound
charges $\epsilon^{b}$($\omega$), since these are important scientifically as
well as technologically: the $\epsilon_1^{b}$(0) of a metal electrode is one of
the major factors determining the depolarization field inside a ferroelectric
capacitor. To obtain $\epsilon_1^{b}$(0), we measured reflectivity spectra of
sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7
meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and
imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings
to extract $\epsilon_1^{b}$(0) values. Ir, Ru, Pt, and IrO$_2$ produced
experimental $\epsilon_1^{b}$(0) values of 48$\pm$10, 82$\pm$10, 58$\pm$10, and
29$\pm$5, respectively, which are in good agreement with values obtained using
first-principles calculations. These values are much higher than those for
noble metals such as Cu, Ag, and Au because transition metals and IrO$_2$ have
such strong d-d transitions below 2.0 eV. High $\epsilon_1^{b}$(0) values will
reduce the depolarization field in ferroelectric capacitors, making these
materials good candidates for use as electrodes in ferroelectric applications.
