The growth of rare-earth (RE) silicides on Si substrates have been subject of both technological and fundamental interest due to the possibility of device applications and the observation of various reconstructed structures [1]. The low Schottky barrier heights (0.3-0.4 eV) of the RE silicides formed on n-type Si(111), and the good epitaxial growth of these silicides have motivated further characterization of them. Dysprosium (Dy) silicide has been reported to show a (1×1) structure, which consists of an ordered hexagonal monolayer of Dy that is located underneath a buckled surface Si layer, at a Dy coverage of 1 ML, and a (√3×√3) reconstruction for thicker films [2]. The (√3×√3) structure is formed by a defected AlB2-type that consists of a surface with buckled Si hexagons, and stacked hexagonal Dy planes and graphite-like Si planes with every sixth Si atom missing [3]. Compared to the knowledge on their atomic structure, little is known on the thickness-dependent electronic structure of Dy silicide films. In this paper, we report detailed photoemission measurements on the electronic structures of Dy silicide films with different thickness. The measurements were performed at BL-18A at KEK-PF, Japan. The formations of a (1×1) monolayer Dy silicide film and (√3×√3) thicker films were confirmed by LEED. On the monolayer film, two prominent surface bands were observed in a binding energy range of 0-1.8 eV. Of these two bands, one follows a (1×1) periodicity and the other one follows a (√3×√3) periodicity. By increasing the film thickness, the photoemission intensity of the (√3×√3) periodic band increased, while the intensity of the (1×1) periodic band decreased. Further, the periodicity of the (1×1) band changed to a (√3×√3) periodicity by increasing the film thickness. These results indicate that the origins of the two bands are different. In our talk, we will discuss the origins of these two bands in more detail.
References
[1] F.P. Netzer, J. Phys.; Condens. Matter 7, 991 (1995).
[2] I. Engelhardt et al, Surf. Sci. 600 755 (2006).
[3] R. Baptist et al., Phys. Rev. Lett. 64, 311 (1990).
[4] P. Wetzel et al, Phys. Rev. B 50 10886 (1994). |