Thursday, March 20, 2008, 10:00 am — Bldg. 480,conference room
Utilizing photostimulated processes on oxide surfaces is essential to photocatalysis, environmentally clean energy production, functional coatings, and photonics. All these applications require a better understanding of the mechanisms that convert photon energy into excited surface states which in turn lead to selective bond breaking, to nonradiative exciton deactivation or to photoluminescence emission from particular sites. Recent advances in the synthesis of morphologically well-defined nanocrystals and the functionalisation of their surfaces have established an unprecedented playground for related photophysics and chemistry studies.
Chemical vapor deposition in conjunction with subsequent vacuum annealing can be used for the production of nanometer-sized MgO cubes with characteristic surface defects [1]. Due to their shape the particle size sets the ratio between corner and edge ions. Corresponding trends are reflected in the optical properties of MgO nanocubes making this material a promising model system for the investigation of photoexcited states at oxide surfaces [1]. Surface anions in edge and corner positions are addressed by monochromatic UV light upon site-selective generation of hole centers at oxygen-terminated corners. On the other hand, the protonation of oxygen-terminated corners alters the photoluminescence emission properties of the underlying surface elements and provides efficient means for manipulating their optical properties [2].
While on highly dispersed alkaline earth oxides UV light with energies below 6.2 eV (l>200nm) exclusively addresses the surface, light induced charge separation is initiated in the bulk of TiO2 based materials. In this context, layered titanate nanostructures have attracted much attention due to a broad spectrum of potential photochemical and electrochemical applications. We found that the surface chemistry induced transformation of their morphologies can be used to control their photoelectronic properties. N
Hosted by: Stan Wong
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