Scanning Probe Microscope (SPM) is a powerful tool not only for imaging but also for manipulation of atomic scale abject. Various kinds of atom switches have been reported for the last several decades. While most of atom switches are induced by tunneling current injected from STM tip, buckled dimer rows (1D-like) on the Si(100) surface are switched by atomic force in unidirectional manner, as recently found in AFM studies. Here, we have introduced Si tetramer (Si4) [1] which is switched by both tunneling current (STM) and chemical force (AFM).
Structure models of bi-stable Si4 in the ground state (Type-A and B) were constructed by first-principles simulation, and confirmed by corresponding STM images using an Omicron LT QPlus-AFM/STM system operated at 80 K. Si4 is switched between two mirror-symmetric configurations by both atomic force and tunneling current. Competition and transition between force-induced (upward) and current-induced (downward) switching is demonstrated. [2]
What happens if such well-defined single Si4 atom switch stay next to another Si4? It is found that twin Si4 preferentially stay “On-On” state. In addition, even switching probability of one Si4 of twin Si4 increases when another Si4 stay “On” state. Therefore, it is concluded that two adjacent Si4 atom switches exhibits interaction.

As introduction of various SPM techniques, high-resolution imaging of single molecule using AFM [2], spatially-resolved electric transport on single/few layer Graphene by using 4-probe STM/STP [3], and electric transport on monatomic layer [4] will be introduced as well.

[1] S. Yamazaki, et al., Nano. Lett., 15, 4356 (2015).
[2] K. Iwata, S. Yamazaki, et al., Nat. Commun. 6:7766 (2015).
[3] J-K. Lee, S. Yamazaki, et al., Nano Lett. 13, 3494 (2013).
[4] S. Yamazaki, et al., Phys. Rev. Lett. 106, 116802 (2011).