Absence of double-bond formation on the Ge(111)3x1-Na surface studied by scanning tunneling microscopy

The structure of the Na-induced 3 X 1 reconstruction of the Ge(111) surface has been examined using scanning tunneling microscopy (STM). The STM image s reveal significant differences from those of the metal-induced Si(111)3 X 1 surfaces. Our interpretation of the images leads us to conclude that unl ike the Si(111)3 X 1 surfaces, there exist no Ge=Ge double bonds on Ge(111) 3 X 1-Na despite the similarity in structure. This raises a serious questio n about a recent proposal that the metal-induced 3 X 1 reconstruction of th e Si(111) surface is stabilized by the formation of a Si=Si double bond. We propose that surface electrostatic energy due to the charge transfer accom panying the surface relaxation plays an important role in stabilizing the G e(111)3 X 1-Na surface, and possibly the metal-induced Si(111)3 X 1 surface s as well.