Eur. Phys. J. B (2013) 86: 477
https://doi.org/10.1140/epjb/e2013-40626-9

Regular Article

Adsorption of oxygen on Mo (112) surface precovered with beryllium: formation of overlayer and electronic properties

Institute of Physics, Natl. Academy of Sciences of Ukraine, Prospect Nauki 46, UA-03680, Kyiv-28, Ukraine

^a e-mail: fedorus.gm@gmail.com

Received: 27 June 2013
Received in final form: 20 September 2013
Published online: 18 November 2013

Abstract

Adsorption of oxygen on the Mo (112) surface precovered with a pseudomorphic monolayer of beryllium has been investigated at room temperature by AES, LEED and contact potential difference methods. Such a Be/Mo (112) substrate is actually a bimetallic surface where closely-packed atomic Mo ridges alternate with rows of Be atoms. It has been found that at small oxygen exposures (Q < 0.3 Langmuir), the initial sticking coefficient for oxygen S_O on Be/Mo (112) is lower by a factor of ~1/15 than on the clean Mo (112) surface where S_O is close to unity. However, with increasing the oxygen coverage above θ_O ≈ 0.1, the sticking coefficient showed a nonlinear growth, and oxygen saturation of the surface was achieved at Q = 1.6–1.7 L. Oxygen adsorption decreases the work function of the Be/Mo (112) surface and gives rise to appearance of some Auger peaks specific to beryllium oxide, which indicates a change in the chemical nature of the surface. The formation of a polar-covalent BeO compound may be responsible for a self-activation of the surface with respect to oxygen which is reflected in the increase of the sticking coefficient observed under growth of oxygen coverage (a kind of autocatalytic reaction). Annealing of the O/Be/Mo (112) system to T_an = 1100 K resulted in an additional decrease of the work function and a growth of the ratio between the Auger signals of Be in the oxide and metallic Be adsorbed phases. The presence of BeO molecules was detected up to T_an = 1600 K, above which they dissociated with desorption of Be.