We have observed large increases in the transition temperature $T_c$ of thin, quenched composite films consisting of alternating layers of dissimilar metals. We estimate the regions of the film which experience the greatest increase to be within a few monolayers of the metal-vacuum or metal-metal surfaces. A possible explanation for the increased $T_c\text{'}\mathrm{s}$ is the shift in the electron-phonon coupling to larger values due to the lowering of the phonon frequencies.

• Received 1 August 1968

DOI:https://doi.org/10.1103/PhysRevLett.21.1320