AVS 54th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA4
An Atomic Seesaw Switch by Tunneling Carrier Injection on Ge (001)

Tuesday, October 16, 2007, 2:40 pm, Room 611

Session: Excitations at Surfaces
Presenter: K. Tomatsu, University of Tokyo, Japan
Authors: K. Tomatsu, University of Tokyo, Japan
K. Nakatsuji, University of Tokyo, Japan
T. Iimori, University of Tokyo, Japan
Y. Takagi, Riken Harima, Japan
H. Kusuhara, Tottori University, Japan
A. Ishii, Tottori University, Japan
F. Komori, University of Tokyo, Japan
Correspondent: Click to Email

Reversible switching of electronic conduction through atom manipulation is one of the main subjects of nanoscience. However, different conducting pathways have not been clearly observed with atomic resolution. Here, we demonstrate the correlation between the change of surface atomic position by tunneling carrier injection and that of the reflection of one-dimensional (1D) surface-state electrons on the Ge (001) surface with a low density of heterogeneous Sn-Ge dimers.1 On the clean Ge(001) surface, two atoms form a buckled dimer, and bonding π- and antibonding π*-states localize on upper and lower atoms of the dimer. The Ge dimers align in the [110] direction and form a dimer row. The π*-electron behaves like a 1D free electron along the dimer row. It has been shown that the buckling orientation of the Ge dimer can be reversibly controlled by surface bias voltage of STM.2 This conformation change is induced by inelastic scattering of injected carriers from the STM tip to the surface under the electric field due to the bias voltage. When Sn atoms are deposited on the clean Ge(001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge dimer position in the surface.3 We identify the dimer as a heterogeneous Sn-Ge dimer by reversing its buckling orientation with STM and observing the change of the STM images at 80 K. An atomic seesaw switch is realized for the 1D π* electrons in the Ge dimer-row direction by using the STM to reversibly flip the buckling orientation of a single Sn-Ge dimer in the dimer row. When the Sn atom of the heterogeneous dimer is at the lower position, the 1D electrons are reflected and a standing wave of this state is observed in the dI/dV image. Whereas, when it is at the upper position, the 1D electrons pass through the heterogeneous dimer, and no standing wave is observed. In this state, the lower atom of the dimer is Ge, and the π* state of the dimer is little different from that of the Ge-Ge dimers. These are confirmed using first-principles calculations.

1K. Tomatsu, K. Nakatsuji, T. Iimori, Y. Takagi, H. Kusuhara, A. Ishii, F. Komori; Science 315, 1696, 2007.
2Y. Takagi, Y. Yoshimoto, K. Nakatsuji, F. Komori; Phys. Rev. B75, 115304, 2007.
3K. Tomatsu, K. Nakatsuji, T. Iimori, F. Komori; Surf. Sci. 601, 1736, 2007.