Metal–insulator transition in a layer adsorbed on a metal electrode

The properties of a layer of metal atoms adsorbed on a metal electrode are investigated as a function of the coverage, focusing on metal–insulator transitions of the Mott–Hubbard type. For this purpose a model Hamiltonian is set up which incorporates the interaction of the adsorbate with the metal and with the solvent, and approximate solutions for the adsorbate Greenʹs functions are derived. The presence of the solvent has a strong effect both on the onsite Coulomb repulsion and on the adsorbate–adsorbate interactions. Metallization requires both a finite density of states near the Fermi level and a mean free path for the electrons exceeding the lattice spacing. Explicit model calculations have been performed for a regular lattice of copper on Au(1 1 1). With increasing coverage, the adsorbate passes from an insulating to a conductive state, then back to an insulating phase before becoming conductive again near full coverage.