Thickness-dependent electron-phonon coupling and transport in metals from first principles

Recent strides in thin-film deposition technology have made the next generation of ultrathin plasmonic devices and ultrascaled metallic interconnects plausible. It has led to a renewed interest in the study of properties of metals and semiconductors in the low dimensional limit. Here, starting with a single layer, we systematically investigate the effect of thickness on the electronic properties and electron-phonon (e-ph) coupling of ultrathin metallic films. Such ab initio studies have typically been challenging because of the inability of the state-of-the-art DFT codes to correctly predict the phonon dispersion curves of finite thickness materials, especially in the q→0 limit. We propose a new computationally-inexpensive correction scheme for the phonon force matrix based on rotational invariance of the elasticity tensor. This scheme facilitates accurate computation of phonon bandstructures and e-ph coupling for arbitrary film geometries. Using this capability, we determine the variation of electronic transport properties as a function of layer number, fully accounting for effects such as phonon confinement. These ab initio calculations give us an insight into the effect of surface and interfacial strain on the e-ph scattering in thin metallic films.