Discrete Electronic Sub-bands without Confinement: Bragg Scattering at Molecular Edges

The discretization of the electronic structure of nanometer-size solid systems due to quantum confinement and the concomitant modification of their physical properties is one of the cornerstones for the development of Nanoscience and Nanotechnology. In this letter we demonstrate that Bragg scattering of Cu(111) surface state electrons by the periodic arrangement of tetracyanoquinodimethane (TCNQ) molecules at the edges of self-assembled molecular islands, discretizes the possible values of the electron momentum parallel to the island edge. The electronic structure consists thus of a discrete number of sub-bands which occur in a non-closed space and, therefore, without quantum confinement.