Joseph M. Carpinelli

Electronic properties of the AgGe(111) interface

Abstract When silver is deposited onto Ge(111)c(2 × 8), the interface may undergo a (3 × 1), (4 × 4), (√3 × √3)R30 and eventually a (6 × 6) reconstruction. By using a scanning tunneling microscope (STM) in the current-imaging tunneling spectroscopy (CITS) mode, we obtained important new information on the electronic properties of these coexisting reconstructions. The c(2 × 8), (3 × 1) and (4 × 4) reconstructions are non-metallic with tunneling gaps of 0.45, 0.85 and 0.85 eV, respectively, while the (√3 × √3)R30° reconstruction is manifestly metallic. Electron energy-loss spectroscopy (EELS) data reveal Δ q | = 0 excitation gaps which match the tunneling gaps from CITS. In addition, EELS indicates that increasing the Ag density in the metallic (√3 × √3)R30° phase initiates a gradual metal-non-metal transition. This transition is completed with the formation of a high-density (6 × 6) reconstruction with a band gap of 0.18 eV. We propose that the (4 × 4), (√3 × √3)R30° and (6 × 6) structures have a Ge trimer unit in common.

Scanning tunneling microscopy study of the metal-induced Si(111)3 × 1 reconstruction: evidence for dimerized chain formation

Abstract Scanning tunneling microscope (STM) images of the Si(111)3 × 1-Ag interface exhibit a strong bias dependence. A clear dimerization of the Si surface atoms is evident from the 1 V empty state images. The imaged electronic states exhibit either a 3 × 1 or a 6 × 1 periodicity. These results are interpreted on the basis of the recently proposed dimerized chain or conjugated chain model. It is demonstrated that the dimer orientation in every second dimer row of the 3 × 1 reconstruction can be changed using a STM tip, thereby producing a 6 × 1 symmetry. This phenomenon could be similar to the well-known soliton excitations in doped conjugated polymers.

Charge rearrangement in the GexPb1−x/Ge(111) interface

Abstract We have investigated a non-metal–metal transition, novel in-plane ordering and STM imaging contrast, all of which evolve as a function of Pb concentration in the two-dimensional solid solution GexPb1−x/Ge(111). The cause of these is a local charge rearrangement between the surface Pb and Ge adatoms.