Gap opening of image potential state on reconstructed Ir(001) surface

Image potential states (IPS) for the unreconstructed Ir⁡(001)−(1×1) and the reconstructed Ir⁡(001)−(5×1) surfaces are investigated by using two-photon photoemission (2PPE) spectroscopy. The Ir⁡(001)−(5×1) reconstructed surface covered by Xe adatoms exhibits a bandgap of 100 meV, which arises from the new periodic potential created by the reconstruction. Meanwhile, no band gap is observed on the unreconstructed Ir⁡(001)−(1×1) surface within a similar momentum range, meaning that the bandgap essentially originates from the surface reconstruction. Further investigation by the planar-averaged charge density distributions of the IPS for both surfaces shows that Xe adsorption does not significantly alter the positions of charge density maxima. It rationalizes why the band gap arising from the substrate superlattice potential does not change significantly upon Xe adsorption. The good agreement between the 2PPE experiments and the theoretical calculations highlights the robustness of IPS behavior under Xe adsorption.