Observation of resonant electron transmission through a Ni/Cu/Ni(100) sandwich structure

Cu(100)films of average thicknesses from 3 to 7 Å have been grown on a Ni(100) substrate and capped with Ni(100) films of varying thickness. Electron transmission through the films was measured as a function of incident electron energy. Features observed above 9.5 eV above the Fermi energy show a strong dependence on the thickness of the Ni outer layer, characteristic of the quantum size effect. A feature below 9.5 eV shows only a weak dependence on the Ni thickness. This feature is suggested to result from resonant transmission through a bound state. The position of the feature as a function of the thickness of the Cu layer is in good agreement with the position for the bound state in a quantum well formed by the offset ${\mathrm{X}}_1$ points of the bulk Ni and Cu band structures.