Size effects in the electronic heat capacity of small platinum particles embedded in silica

Heat-capacity measurements on sputtered granular metal films of Pt-Si${\mathrm{O}}_2$ were carried out between 1 and 12 °K. Mean sizes of the Pt particles range from 10 to 26 Å; this small size coupled with these low temperatures makes the average electronic-energy-level spacing $\delta$ in the Pt metal large compared to $k_{B}T$. A quantum size effect in the electronic heat capacity of a metal has been predicted in this limit, $\delta \gg k_{B}T$, and is observed here for the first time, although in a very limited temperature range. Difficulity in observing this size effect was caused by a large heat-capacity enhancement over bulk values in the insulating vitreous silica. This enhancement is ascribed to the Pt particle inclusions in the host Si${\mathrm{O}}_2$ matrix augmenting the low-frequency Einstein modes first observed in the specific heat of Si${\mathrm{O}}_2$ by Flubacher et al.