Understanding nc-AFM contrast on TiO2 and water adsorption on CeO2
Departamento de Física Teórica de la Materia Condensada, UAM
Metal oxides are important for a wide range of technological applications . In order to optimize these proccesses or find new ones it is essential to understand their surface properties and chemistry in detail. Atomically-resolved scanning probe microscopy techniques, like non-contact atomic force microscopy (nc-AFM) , combined with theoretical simulations play a crucial role in this respect. In this seminar I will give an overview of our recent and ongoing work on two representative oxide surfaces: TiO2(110) and CeO2(111). I will start by showing how a combination of site-speciﬁc force spectroscopy measurements on TiO2(110) and ﬁrst-principles calculations clarifies the origin of the nc-AFM contrast and let us characterize the tip structures responsible for the two most common imaging modes . The same model tips can be applied to related systems, like single metal atoms (K, Pt) adsorbed on TiO2(110). I will then consider the problem of water adsorption and pre-dissociation on CeO2(111). When modelling ceria, one has to be specially careful with the approach used for the exchange-correlation functional, as the surface is easily reduced, and the electrons tend to localize on f-states . For water on the clean surface, all our first-principles simulations performed at different levels of theory point to the same solution: water can be adsorbed either molecularly or pre-dissociatively, with adsorption energies in agreement with the experimental data available, and a small barrier (about 0.15 eV) connecting the two structures . Finally, I will show some preliminary results for hydrogen adsorption and dissociation on CeO2(111).
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