Copper (260 nm) and Ag (1000 nm) films deposited on glass substrates, at
different substrate temperatures. Their optical properties were measured by
ellipsometry (single wavelength of 589.3 nm) and spectrophotometry in the
spectral range of 200–2600 nm. Kramers Kronig method was used for the
analysis of the reflectivity curves of Cu and Ag films to obtain the optical
constants of the films, while ellipsometry measurements was carried out as
an independent method. The influence of substrate temperature on the
microstructure of thin metallic films [Structure Zone Model (SZM)] is well
established [Movchan and Demchishin, Phys. Met. Metall. 28, 83 (1969); Thornton, J. Vac. Sci. Technol. 12, 830 (1975); Savaloni
and Bagheri Najmi, Vacuum 66, 49 (2002); Savaloni and Player, Vacuum 46, 167 (1995); Savaloni et al., Vacuum 43, 965 (1992)]. The Effective Medium Approximation (EMA)
analysis was used to establish the relationship between the SZM and EMA
predictions. Good agreements between SZM as a function of substrate
temperature and the values of volume fraction of voids obtained from EMA
analysis, is achieved; by increasing the substrate temperature the
separation of the metallic grains decreases, hence, the volume fraction of
voids decreases and denser films formed.
The predictions of the Drude free-electron theory are compared with
experimental results for dielectric functions of Cu and Ag films of
different substrate temperature. The real part of the dielectric constant is
decreased with increasing the substrate temperature, while the imaginary
part of the dielectric constant increased with temperature for both
materials over the whole energy range measured, including intraband and
interband regions. The increase of the imaginary part in the interband
region suggests a temperature and frequency dependence of the relaxation
time in the Drude model, namely $\tau ^{-1}\left( \omega \right)=\tau
_0^{-1} +\beta \omega ^2.$