The evolution of electronic structures, surface phonons, and electron-phonon interactions with the slab thickness in Al(100) and Al(111) films is studied from density functional perturbation theory. Our results clearly show a periodic oscillatory behavior of the calculated interlayer relaxations, surface energies, total density of states at the Fermi level, surface phonon states, electron-phonon coupling constant $\lambda$, and even the transition temperature $T_C$ of superconductivity as a function of the slab thickness for Al(111) films. However there is no clear periodic oscillation found for Al(100) films. The different oscillatory behavior of physical properties between Al(111) and Al(100) films is discussed by considering the crystal band structure. For both Al(111) and Al(100) slabs, the values of $\lambda$ and $T_C$ obtained in this work at small slab thickness greatly exceed their bulk values. Both electronic confinement and the softening of surface phonons contribute to the enhancement of superconductivity for films at small thickness.

• Received 1 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.214514