Point Defects and Related Excess Electrons in the Dielectric Prole of the Reduced TiO 2 (110) Surface

International audienceThe dielectric behavior of the reduced TiO 2 (110) rutile surface has been explored by High-Resolution Electron Energy Loss Spectroscopy as a function of oxygen exposure, temperature and crystal orientation (dielectric anisotropy) to highlight at once the electrical transport of excess electrons and the associated band gap states (BGS), and to establish a dielectric model that encompasses the surface region as a whole. Never explored distribution proles were determined in two steps: charge carriers and then defects themselves. Firstly, surface and bulk carrier excitations were directly evidenced by the temperaturedependent broadening of the quasi-elastic peak and changes in loss features, which legitimates ts via a previous dielectric model accounting for phonons, interband transitions, plasmon excitations and BGS. The density prole of excess electrons, involving a dead zone, a rich subsurface and a lower bulk concentration was quantitatively optimized. Surface and bulk concentrations, donor and Fermi levels match tabulated values. In a second step, three types of defects were distinguished i.e. O b (vac), surface Ti int and bulk Ti int thanks to changes in surface and bulk plasmon and BGS strengths upon oxygen exposure of the reduced surface. Each of them exhibits a specic behavior. While the surface conductivity requires the presence of O b (vac), both O b (vac) and surface Ti int participate in surface reactions and all three species contribute to band bending which evidences that defects, alone or by cross inuences, shape the location and the properties of excess electrons. Making it crucial to take into account the fact, often overlooked, that excess electrons do not behave independently of their source, the nding suggests studying defects taken individually or within controlled combinations