Pt Nanowires on Ge(001) : sheep in wolf's clothing?

The deposition of small amounts of Pt on a Ge(001) surface gives rise to the formation of monatomic nanowires (NW). These NW are defect- and kink-free and their length is only limited by the underlying beta-terrace, to which the NW are uniquely connected.[1] In this density functional theory (DFT) study, we investigate the structure of the nanowires and the underlying beta-terrace. Through a carefull study of the calculated formation energies and a direct comparison of the experimental scanning tunneling microscopy (STM) images and calculated STM images, we are able to propose both a formation path and a structural model for the NWs. Our results show the beta-terrace to have a structure similar to the clean Ge(001) surface with one in four Ge atoms replaced by a Pt atom, giving rise to a checkerboard pattern. For the NW, we come to the remarkable conclusion that the observed NW consist of Ge instead of Pt.[2] The calculated STM images of this model show perfect agreement with the experimental low temperature STM images, and allow for all features observed in experiment to be assigned to specific atomic species, adding chemical sensitivity to the technique of STM. Furthermore, we show that this model is consistent with CO adsorption experiments.[3] [1] O. Gurlu et al.,Appl. Phys. Lett. 83, 4610 (2003). [2] D.E.P. Vanpoucke and G. Brocks, Phys. Rev. B 77, 241308(R) (2008). [3] D.E.P. Vanpoucke and G. Brocks, Phys. Rev. B 81, 235434 (2010