Self-consistent study of electron confinement to metallic thin films on solid surfaces

We present a method for density-functional modeling of metallic overlayers grown on a support. It offers a useful tool to study nanostructures, combining the power of self-consistent pseudopotential calculations with the simplicity of a one-dimensional approach. The model is illustrated for Pb layers grown on the Cu(111) surface. The analysis provides the strength of the electron confinement barriers in thin slabs with accuracy, supporting the interpretation of the quantum well state spectra measured by scanning tunneling spectroscopy. On the other hand, it offers a benchmark to check the simple analytical models commonly used in the literature to study metallic films on semiconducting or metallic surfaces. As a result, some deficiencies are detected in the applicability of those models, which often lead to an overestimation of the number of wetting layers. Finally, an improved formula is proposed.