Structural and electronic properties of Ge-Si, Sn-Si, and Pb-Si dimers on Si(001) from density-functional calculations

Using first-principles methods we studied structural and electronic properties of asymmetric heterogeneous X-Si (X=Ge, Sn, and Pb) dimers on the Si(001) surface and their scatterings for the quasi-one-dimensional π electrons. The X-Si dimer with impurity atom X at the lower position scatters more strongly the π electrons than that with X at the upper position. Calculated scattering potentials can be qualitatively explained by the difference in p -orbital energy between Si and the lower atom of the X-Si dimer. We predict that the amplitude of electronic standing waves changes significantly between the two oppositely buckled X-Si dimers in differential conductance images of scanning tunneling microscopy. This suggests the possibility of fabricating atomic switches to control the conduction of π electrons along the dimer row. Our proposed atomic switches could be achieved by flipping the impurity dimers on the Si(001) surface using the method developed in recent experiments. Finally, we proposed the model for dimer-flipping mechanism, which can explain previous experiment.