Image states on a free-electron metal surface covered by an atomically thin insulator layer

Excited electronic states on a free-electron metal surface are investigated in the case when an atomically thin Ar layer is adsorbed on the surface. It is shown that the dielectric character of the Ar layer allows the existence of image states as well-defined resonances in this system. The image states are confined in vacuum by the Ar layer and decay by electron transmission through the Ar layer. A 3D microscopic description of the Ar layer associated to a wave-packet propagation approach is used to determine the characteristics, energy and lifetime, of the image states in a model Ar/free-electron metal system. The possibility of the observation of these states in a time-resolved experiment is discussed.