Electric-field effects on the diffusion of Si and Ge adatoms on Si(001) studied by density functional simulations

We present results of density functional theory (DFT) calculations of the electric-field effects on the clean Si(001) surface and the diffusion of Si or Ge adatoms on Si(001) surface. Our results indicate that the electric field only slightly affected the dimer bond lengths and buckling angles of the clean Si(001), implying that the electric field of scanning tunneling microscopy tip should not be responsible for the observation of symmetric dimers and the flip-flop motion of the buckling dimers. Also, the electric field mainly influences the diffusion along the dimer row, and the diffusion barrier could be reduced greatly under a positive electric field. It can be expected that the positive field should make the diffusion of Si or Ge adatoms on the Si(001) surface become more anisotropic.