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Photoemission Electron Microscopy of TiO 2 Anatase Films Embedded with Rutile Nanocrystals
Author(s) -
Xiong G.,
Shao R.,
Droubay T. C.,
Joly A. G.,
Beck K. M.,
Chambers S. A.,
Hess W. P.
Publication year - 2007
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200700146
Subject(s) - anatase , photoemission electron microscopy , materials science , rutile , nanocrystal , work function , excited state , nanocrystalline material , nanotechnology , chemical physics , optics , chemical engineering , electron microscope , photocatalysis , atomic physics , chemistry , biochemistry , physics , engineering , catalysis , layer (electronics)
Photoemission electron microscopy (PEEM) excited by X‐ray and UV sources is used to investigate epitaxial anatase thin films with embedded rutile nanocrystals, a model system for the study of heterocatalysis on mixed‐phase TiO 2 . Both excitation sources show distinct contrast between the two TiO 2 phases; however, the contrast is reversed. Rutile nanocrystals appear darker than the anatase film in X‐ray PEEM images but brighter in UV‐PEEM images. We observe that topography‐induced contrast is dominant in X‐ray PEEM imaging, whereas work function and density‐of‐state‐based contrast, dominates in UV‐PEEM. This assertion is confirmed by UPS and conducting AFM data that shows the rutile work function to be 0.2 eV lower and a greater occupied valence band density‐of‐states in rutile (100) than in anatase (001). Since the boundaries between rutile nanocrystals and the anatase film are clearly resolved, these results indicate that PEEM studies of excited state dynamics and heterocatalysis are possible at chemically intriguing mixed‐phase TiO 2 interfaces and grain boundaries.