Electron Microscopic Investigations And First-principles Calculations Of Metal-oxide Surfaces And Interfaces

Numerous catalytic reactions are involved in industrial production,which often occur mainly at the surface and interface positions of catalysts.The surface and interface of materials often exhibit unique physical and chemical properties that are different from the bulk.The atomic structure and electronic structure of the surface and interface are the most direct factors affecting the catalytic performance of materials,determining the specific processes of catalytic reaction and catalytic efficiency.Accurately analyzing the surface and interface structures of metal oxide supports will provide direct guidance for designing new catalyst systems according to actual needs.Herein,three typical metal oxides,CeO2(with fluorite structure)nanoparticles,NiO(with rock-salt structure)single crystals,and CuO(with monoclinic structure)thin films,were selected as the research objects.The atomic structures of the material surface and interface were characterized using aberration-corrected(scanning)transmission electron microscopy,and combined with first-principles calculations,the electronic properties of these metal oxide surface and interface were systematically studied,and the effects of defects on the structural stability of surface and interface were explored.This work has universal significance for the study of the surface and interface of metal oxides,improves the understanding of the surface microstructure of catalysts,and provides a reliable theoretical basis for further research on the catalytic mechanism of oxides.Firstly,the ceria nanoparticles were prepared by hydrothermal method and the surface of CeO2(111)was accurately analyzed.It was found that surfaces terminated with O atoms can be stably existent.Simultaneously,simultaneous loss of surface and subsurface oxygen close to a highly reducible Ce-terminated step was observed.The calculation results reveal that CeO2 can show a metastable surface with high defect concentration due to the influence of electron beam irradiation and oxidation potential,unveiling the complex surface behavior of CeO2.Secondly,the atomic structure of NiO(111)twin boundary was directly confirmed experimentally,that is,the twinning occurs on the(111)plane,with oxygen atoms located at the twin boundary.Combined with theoretical calculations,the results indicate that the located oxygen atoms at the twin boundary is more conducive to reducing the twin boundary energy,and twin structure with antiferromagnetic coupling between the mirroring Ni atomic planes near the twin boundary has lower boundary energy.Finally,epitaxial CuO thin films were grown on ZnO(0001)single crystal substrate by pulsed laser deposition,and a completely coherent CuO/ZnO interface and CuO(001)twins were obtained.The atomic,magnetic,and electronic structures of the CuO/ZnO interface and the CuO(001)twin boundary were studied by combining experimental characterization and theoretical calculations.It was detected that the orientation relationship of CuO/ZnO interface was CuO[110](111)ZnO[1120](0001)and CuO was found to be tended to form AFM(111)configuration.The interface may have the characteristics of two-dimensional electron gas.Nevertheless,the CuO(001)twin boundary remains insulating and havs a magnetic configuration of AFM(101).