Bismuth deposition on silicon (001) surface (near the Bi desorption temperature, 500oC) gives rise to self-organized Bi lines. Such lines have the lateral width of only 1.5 nm, and can be grown up to 500 nm in length, being free defects. It is generally agreed that these are semiconduncting in nature [1-3]. The electronic states within the substrate band gap are attributed to the Si dimers. The remarkable straightness of the Bi nanolines makes them very attractive as a template for deposition of other elements. Indeed, there are some studies addressing the deposition of In, Ag and most recently Fe along the Bi nanolines [4,5]. In particular, the iron adsorption on semiconductor surfaces is quite interesting due to the possible formation of iron silicide thin films [6].
In this report we present an ab initio total energy investigation of quasi one dimensional iron stripes patterned by Bi nanolines. The calculations were performed by using the density functional theory, within the local density approximation. The electron-ion interactions were treated by norm conserving pseudopotentials for Bi and Si, whereas Fe was described by ultrasoft pseudopotentials. We have used an energy cutoff of 25 Ry, for the plane wave basis set. The surface was described within a repeated slab method, with 2x6 surface unit cell and 10 monolayers of silicon.
We find that the Fe adsorption aside Bi nanolines represents an energetically favorable configuration for low (sub-monolayer) iron coverages. With increased sub-monolayer coverages, Fe adatoms tend to adsorb close to each other, giving rise to an anti-ferromagnetic iron line aside the Bi nanolines. Further increase of Fe coverage (closer to a manolayer) induces the formation of stripes of iron-silicide patterend by Bi nanolines.
References:
[1] R.H. Miwa, J.M. MacLeod, A.B. McLean, and G.P. Srivastava, Nanotech. 16, 2427 (2005).
[2] D.R. Bowler, J.H. Owen, and K. Miki, Nanotech. 17 1801 (2006).
[3] R.H. Miwa, J.M. MacLeod, A.B. McLean, and G.P. Srivastava, Nanotech. 17 1803 (2006).
[4] J.H. Owen, and K. Miki, Nanotech. 17, 430 (2006).
[5] Hiroaki Koga and Takahisa Ohno, Phys. Rev. B 75, 125405 (2006).
[6] W. Orellana, and R.H. Miwa, Appl. Phys. Lett. 89, 093105 (2006).
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