Reference plane for the electronic states in thin films on stepped surfaces

During the photoemission process the parallel component of the photoelectron momentum is conserved across the modulation plane of the wavefunction, which is the so-called reference plane. The identification of this plane is straightforward for low Miller-index surfaces, but questionable for surfaces of lower symmetry. In this work, the authors show experimentally the coexistence of two different reference planes for surface and bulklike quantum-well states of thin nanostructured films grown on a regularly stepped substrate.