Experimental and theoretical evidence for substitutional molybdenum atoms in the TiO 2 ( 110 ) subsurface
2006; American Physical Society; Volume: 73; Issue: 24 Linguagem: Inglês
10.1103/physrevb.73.245433
ISSN1550-235X
AutoresB. Domenichini, Gian Andrea Rizzi, Péter Krüger, Michela Della Negra, Zheshen Li, M. Petukhov, Gaetano Granozzi, Preben J. Møller, Sylvie Bourgeois,
Tópico(s)Advanced Photocatalysis Techniques
ResumoMolybdenum was deposited at room temperature on the ${\mathrm{TiO}}_{2}(110)$ surface in the 0--1.3 equivalent monolayer (eqML) range and was then annealed at $400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in order to reach a kind of equilibrium state. A threshold was found in the behavior of the deposit: below 0.2 eqML, substitutional molybdenum occurs in titanium sites located under the bridging oxygen atoms of the ${\mathrm{TiO}}_{2}(110)$ surface. In this position, molybdenum atoms are in a structural and chemical ${\mathrm{MoO}}_{2}$-like environment. Density-functional theory calculations show that this molybdenum site is actually the most stable one in the case of isolated molybdenum atoms. Angle-scanned photoelectron diffraction data are in perfect agreement with such a hypothesis. For deposits higher than 0.2 eqML, the increased amount of molybdenum atoms raises the probability of $\mathrm{Mo}\text{\ensuremath{-}}\mathrm{Mo}$ interactions during the annealing at $400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, taking to a reduction process of the deposit. However, such annealing does not allow the deposit to become fully metallic: molybdenum clusters formed during the annealing are in strong interaction with the substrate, and metallic molybdenum can be obtained only depositing a film thicker than $1\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$.
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