Functionalization of Cuprous Oxide: From Doped Binary to Cu-based Ternary Oxide Films

• Applicant: Professor Dr. Niklas Nilius
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 385079232

The present proposal is a follow-up to previous DFG project that aimed at the preparation and characterization of cuprous oxide films with surface science methods. The expired project successfully clarified a number of fundamental questions in connection with Cu2O, a material of enormous scientific and technological relevance. The main advances concern: (i) the kinetics and thermodynamics of Cu-oxidation as probed at defined reaction conditions. For this purpose, a new optical technique was developed for the in-situ monitoring of oxidation fronts and used to establish a Cu-O phase diagram as a function of pressure and temperature(ii) the nature of Cu-O monolayer films grown on Au(111), Pt(111) and Mo(001). The experiments revealed the impossibility to grow thick Cu-oxide films in a vacuum environment(iii) a recipe to grow bulk-type Cu2O films via a high-pressure oxidation scheme(iv) the structural elucidation of the Cu2O(111) surface that always reconstructs and comprises neither low-coordinated Cu ions nor O vacancies, in contrast to all existing literature models.The availability of a new preparation scheme for bulk-type Cu2O(111) represents a firm basis to address other properties of this fascinating material during a follow-up project with these key aspects: (i) Characterization of lattice defects that dominate the electronic (p-type conductance) and chemical properties of the material(ii) Spatially resolved detection of excitons, as the fundamental optical mode of Cu2O, and their interplay with lattice imperfections(iii) Release of the dipole-forbidden nature of band gap recombination in Cu2O via doping and subsequent insertion of defect states at the band edges with favorable parity for optical transitions (iv) Extending the doping scheme towards ternary Cu-based oxides with novel optical and chemical properties, e.g. CuAlO2 and Cu2V2O7 for the photo-catalytic splitting of water.All experiments are performed with state-of-the art surface-science techniques in an UHV environment, in particular with scanning tunneling and optical nearfield microscopy at the atomic level, and will be accompanied by high-level DFT calculations.

• DFG Programme: Research Grants
• International Connection: France
• Major Instrumentation: LN2-cooled CCD spectroscopy system
• Instrumentation Group: 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek)
• Cooperation Partners: Jacek Goniakowski, Ph.D.; Professorin Claudine Noguera, Ph.D.