Image potential states of 2D materials

Two-dimensional materials are currently among the most intensively studied topics in condensed matter physics because of their intriguing properties and the possibilities of integration in future electronic device applications. Image potential states, i.e. two-dimensional unoccupied electronic states that are confined in front of a surface, can provide detailed information on work function, electric field effects, charge transfer, charge injection, and charge dynamics at surfaces. This information is essential to understand and tailor the properties of two-dimensional materials for electronic device applications. In this work, we briefly review recent developments in the detection and analysis of image potential states in single- and multilayered two-dimensional materials, heterostructures thereof, and nanostructures, such as nanoislands and nanoribbons. We also address several issues that can have an effect on image potential states, such as the preparation method, quality of the material, defects, interfacial interactions, and interactions with the substrate.