The equilibrium geometry and electronic structure of Bi nanolines on clean andhydrogenated Si(001) surfaces

Abstract

The equilibrium geometry, electronic structure and energetic stability of Bi nanolines onclean and hydrogenated Si(001) surfaces have been examined by means of ab initio totalenergy calculations and scanning tunnelling microscopy. For the Bi nanolines on a clean Sisurface the two most plausible structural models, the Miki or M model (Miki et al 1999Phys. Rev. B 59 14868) and the Haiku or H model (Owen et al 2002 Phys. Rev. Lett. 88226104), have been examined in detail. The results of the total energy calculations supportthe stability of the H model over the M model, in agreement with previous theoreticalresults. For Bi nanolines on the hydrogenated Si(001) surface, we find that an atomicconfiguration derived from the H model is also more stable than an atomic configurationderived from the M model. However, the energetically less stable (M) model exhibitsbetter agreement with experimental measurements for equilibrium geometry. Theelectronic structures of the H and M models are very similar. Both models exhibit asemiconducting character, with the highest occupied Bi-derived bands lying at∼0.5 eV below the valence band maximum. Simulated and experimental STM images confirm thatat a low negative bias the Bi lines exhibit an ‘antiwire’ property for both structural models.