Studies on ultra-dense recording using probe-induced phase transition

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The purpose of the present study is to establish a new technology for ultra-dense recording utilizing a new phenomenon, probe-induced electronic phase transition. We have succeeded in introducing mesh-like domain structure of a nanometer scale in a layered compound 1T-TaS2 and its derivatives, by appropriately setting the crystal growth condition. By analyzing the atomic arrangements around the domain boundaries in detail, we attributed the mesh-like domain to the mismatch of charge density wave (CDW) lattice along the c-axis.1T-TaS2 is known to show a metal-to-insulator transition around T(MI)=180 K with decreasing temperature. Even above T(MI), surprisingly, we found that each metallic domain can be transferred into insulating states by scanning an STM probe over it. This implies that we can record one bit on each pixel. The minimum size of the domain is 5 nm x 5 nm so that we may be able to realize tera bit/inch2 level recording. All written information can be erased by heating the system far above T(MI). In order to perform the probe-induced phase transition described above, we have to carefully control temperature. In pure 1T-TaS2 crystals synthesized at sulfur poor atmosphere, the writing process can be conducted under more unrestricted conditions, e.g. at 77 K.The crystal includes the characteristic mesh-like domains, and does not indicate bulk metal-insulator transition, suggesting the metastable metallic state is frozen even below the thermodynamic T(MI) point. Thus, if one can introduce more distortion of CDW lattice, it seems possible to perform nano-scale writing even at room temperature.