  The influence of size effects on the thermoelectric properties of thin
platinum films is investigated and compared to the bulk. Structural properties,
like the film thickness and the grain size, are varied. We correlate the
electron mean free path with the temperature dependence of the electrical
conductivity and the absolute Seebeck coefficient $S_{\text{Pt}}$ of platinum.
We use a measurement platform as a standardized method to determine
$S_{\text{Pt}}$ and show that $S_{\text{Pt,film}}$ is reduced compared to
$S_{\text{Pt,bulk}}$. Boundary and surface scattering reduce the
thermodiffusion and the phonon drag contribution to $S_{\text{Pt,film}}$ by
nearly the same factor. A detailed discussion and a model to describe the
temperature dependence of the absolute Seebeck coefficient and the influence of
size effects of electron-phonon and phonon-phonon interaction on
$S_{\text{Pt}}$ is given.
