Reversible switching of electronic conduction through atom manipulation is one of the main subjects of nanoscience. However, the switching of different conducting pathways has not been clearly observed with atomic resolution. Here, we demonstrate the correlation between the change of surface atomic position and that of the reflection of one-dimensional (1D) surface-state electrons on the Ge (001) surface with a low coverage of Sn atoms.[1]
On the clean surface, two Ge atoms form a buckled dimer, and bonding π- and antibonding π*-states localize on upper and lower atoms of the dimer. The dimers align in the [110] direction and form a dimer row. The π*-electron behaves like a 1D free electron along the dimer row. Recently, it was 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 during STM observation at 80 K. An atomic seesaw switch is realized for the 1D π* electrons 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 configuration, 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.
Reference
1. K. Tomatsu, K. Nakatsuji, T. Iimori, Y. Takagi, H. Kusuhara, A. Ishii, F. Komori; Science, 2007, in press.
2. Y. Takagi, Y. Yoshimoto, K. Nakatsuji, F. Komori; Surf. Sci. 559, 1, 2004.
3. K. Tomatsu, K. Nakatsuji, T. Iimori, F. Komori; Surf. Sci., 2007, in press.
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