Crystal electron binding energy and surface work function control of tin dioxide

The work function of a material is commonly used as an intrinsic reference for band alignment; however, it is notoriously susceptible to extrinsic conditions. Following the classification of Bardeen we calculate values for the bulk binding energy of electrons in rutile-structured SnO₂ and the effect of the surface on the work function, thus highlighting the role of the surface in determining the energy levels of a material. Furthermore we demonstrate how, through the use of ultrathin heteroepitaxial oxide layers (SiO₂, TiO_2, PbO₂) at the surface, the work function can be tuned to achieve energy levels commensurate with important technological materials. This approach can be extended from transparent conducting oxides to other semiconducting materials.