ISSN 1063-7834, Physics of the Solid State, 2011, Vol. 53, No. 3, pp. 616–621. © Pleiades Publishing, Ltd., 2011. Original Russian Text © I.I. Pronin, M.V. Gomoyunova, S.M. Solov’ev, O.Yu. Vilkov, D.V. Vyalikh, 2011, published in Fizika Tverdogo Tela, 2011, Vol. 53, No. 3, pp. 573–578. 616 1. INTRODUCTION Interaction of cobalt atoms with the surface of sin- gle-crystal silicon has been dealt with in a wealth of publications whose brief review can be found in [1–3]. Most of the studies explored formation of epitaxial CoSi 2 films which hold considerable promise in the realm of microelectronics. We have been witnessing recently a surge of interest in Co/Si magnetic hetero- structures which appear potentially promising in con- nection with the possibility of their integration with standard electronic devices fabricated by silicon-based technology [4–6]. Development of novel devices which would involve these components requires detailed understanding of how the Co/Si interface undergoes ferromagnetic ordering in the course of its formation. Literature is, however, close to lacking the relevant information. The reason for this lies appar- ently in the high reactivity of the interface and fast oxi- dation of thin cobalt films when exposed to air, which makes it necessary to analyze their magnetic proper- ties in situ under ultrahigh vacuum. We are aware of only a few studies [7–9] which explored ultrathin cobalt layers formed on only one silicon face, Si(111). The first of them, which made use of the Kerr surface magneto-optical effect, revealed that, in the early stage of metal deposition (up to 2.1 Co monolayer), a “dead” magnetic layer evolves on the silicon surface, which is believed, by the authors’ opinion, to be most probably the Co–Si solid solution. Later publications [8, 9] showed that cobalt films formed in the 3–9 monolayer coverage interval (2.4–7.2 Å) are ferro- magnetic, with the easy magnetization axis tilted away from the surface by the angle related with the rough- ness of the growing layer. Note, however, that no anal- ysis of the chemical phase composition of growing films was performed in the above publications. This study represents an attempt at broadening the range of the objects of potential interest by investigat- ing for the first time the initial stages of Co film growth on another important silicon face, Si(100). The goal of the study was to relate the phase composition and electronic structure of growing films with their mag- netic properties. 2. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUE The experiments were performed at the Russian- German laboratory at the HZB BESSY synchrotron (Berlin). Cobalt films were grown on an atomically clean Si(100)2 × 1 surface in ultrahigh vacuum (6 × 10 –10 mbar). The deposition rate was 0.3 Å/min. The samples to be studied were cut from plates of KÉF-1 single-crystal silicon whose surface tilted away from the (001) plane by no more than 0.2°. The sample sur- face was cleaned ex situ by the standard Shiraki treat- Initial Stages of the Growth and Magnetic Properties of Cobalt Films on the Si(100)2 × 1 Surface I. I. Pronin a, *, M. V. Gomoyunova a , S. M. Solov’ev a , O. Yu. Vilkov b, c , and D. V. Vyalikh c a Ioffe Physical-Technical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia * e-mail: Igor.Pronin@mail.ioffe.ru b St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia c Institut für Festkörperphysik, Technische Universität Dresden, Helmholtzstraße 10, Dresden, 01069 Germany Received July 14, 2010 Abstract—The initial stages of the growth of cobalt films on the Si(100)2 × 1 surface and the dynamics of vari- ation in their phase composition, electronic structure, and magnetic properties with a coverage increasing in the range 1–20 Å have been studied by high-resolution photoelectron spectroscopy with synchrotron radia- tion and magnetic linear dichroism in Co 3p electron photoemission. It has been shown that a film of metallic cobalt starts to grow at a coverage of ~7 Å. This process is preceded by the stages involving the formation of the interface cobalt silicide and the Co–Si solid solution. It has also been demonstrated that, at coverages below 15 Å, the sample surface is coated by segregated silicon. The ferromagnetic ordering of the film in the surface plane has been found to follow a threshold character and set in at a coverage of ~6 Å. A further increase in the coverage in the range 8–16 Å is accompanied by a slower increase in the remanence of the film. DOI: 10.1134/S1063783411030243 SURFACE PHYSICS