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Catalytic oxidation of Mo by caesium oxides
Author(s) -
Soriano L.,
Trigo J. F.,
Galán L.,
Rueda F.
Publication year - 1992
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.7401901103
Subject(s) - overlayer , suboxide , caesium , x ray photoelectron spectroscopy , oxide , catalysis , substrate (aquarium) , oxygen , layer (electronics) , inorganic chemistry , catalytic oxidation , chemistry , diffusion , materials science , chemical engineering , nanotechnology , metallurgy , biochemistry , oceanography , physics , organic chemistry , engineering , thermodynamics , geology
The oxidation of a clean Mo surface with different caesium oxide overlayers has been studied by means of x‐ray photoelectron spectroscopy. The results show that the presence of a caesium oxide overlayer produces enhanced oxidation of Mo at room temperature when compared with thermal oxidation, and that a layer of MoO 3 is formed on top of the Mo substrate. The thickness of this MoO 3 layer depends on the thickness of the caesium oxide overlayer. Also, true catalytic oxidation has been observed when the substrate with the caesium oxide overlayer is exposed to oxygen at room temperature. The interface of the MoO 3 layer with the Mo metal consists of about five monolayers of Mo suboxide MoO x (with x ∼2) when the oxidation has been performed at room temperature. At moderate temperatures (∼400 K) this interface is smoother, although it tends to decrease in thickness with time. A mechanism of catalytic oxidation that is consistent with the experimental data is proposed. This mechanism is controlled by diffusion of oxygen through the caesium oxide overlayers and through the Mo substrate. Also, a diffusion of Cs towards the surface has been detected. Different phases of the type MoO 3−δ can explain the chemical shifts observed in the Mo 6+ XPS spectra.