Electronic properties of STM-constructed dangling-bond dimer lines on a Ge(001)-(2×1):H surface

Abstract

Atomically precise dangling-bond (DB) lines are constructed dimer-by-dimer on a hydrogen-passivated Ge( 001)-( 2×1):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.

Fermi level pinning at the Ge(001) surface—A case for non-standard explanation

“…Further details of the preparation process may be found in Ref. 8. Prepared samples were transported in the UHV conditions to the surface transport measurement chamber or to the STM chamber.…”

“…There is no additional surface-related feature close to the Fermi level seen in the ARPES experiments. The unoccupied surface bands are above the lower bulk conductance bands 8 .…”

Appearance of effective surface conductivity: An experimental and analytic study

“…There are well defined surface bands for the clean Ge(001) surface [13] close to the Fermi level. The Ge(001):H surface is isolating due to band positions far from the Fermi level [3,12,14]. The surface treated with the electron beam is supposed to be a disordered system, hence it is weakly conducting at best.…”

“…The hydrogen termination of the surface was done following the procedure reported in Ref. 12 Figure 1. Conductivity σ as a function of the distance D between the current source and drain for three different germanium surfaces.…”

Imaging, single atom contact and single atom manipulations at low temperature using the new ScientaOmicron LT-UHV-4 STM

“…This is for example the case for atomic scale transport measurements in a planar configuration on a surface [15], for transport measurements along dangling bond (DB) atomic wires atom by atom constructed on a passivated semi-conductor surface [16][17][18][19] and for molecule mechanics with the expected measurement of the motive power of a single molecule motor [20,21]. For example, a complete test of the functioning of the recent atom by atom constructed NOR/OR Boolean logic gate on Si(1 0 0)H [22] is demanding at least 4 atomic scale electrical access to this gate.…”