Electronic properties of STM-constructed dangling-bond dimer lines on a Ge(001)-(2x1):H surface

Atomically precise dangling-bond (DB) lines are constructed dimer-by-dimer on a hydrogen-passivated Ge(001)-(2x1):H surface by an efficient scanning tunneling microscope (STM) tip-induced desorption protocol. Due to the smaller surface band gap of the undoped Ge(001) substrate compared to Si(001), states associated with individually created DBs can be characterized spectroscopically by scanning tunneling spectroscopy (STS). Corresponding dI/dV spectra corroborated by first-principle modeling demonstrate that DB dimers introduce states below the Ge(001):H surface conduction band edge. For a DB line parallel to the surface reconstruction rows, the DB-derived states near the conduction band edge shift to lower energies with increasing number of DBs. The coupling between the DB states results in a dispersive band spanning 0.7 eV for an infinite DB line. For a long DB line perpendicular to the surface reconstruction rows, a similar band is not formed since the interdimer coupling is weak. However, for a short DB line (2-3 DBs) perpendicular to the reconstruction rows a significant shift is still observed due to the more flexible dimer buckling.