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

本研究的目的是建立一种新的技术，超密集记录利用一种新的现象，探针诱导的电子相变。通过适当地设定晶体生长条件，我们成功地在层状化合物1 T-TaS 2及其衍生物中引入了纳米尺度的网状畴结构。通过对畴界周围原子排列的详细分析，我们将这种网状畴归因于电荷密度波（CDW）晶格沿着c轴的失配。1 T-TaS 2在T（MI）=180 K附近随温度的降低表现出金属-绝缘体相变。令人惊讶的是，即使在T（MI）以上，我们发现每个金属畴可以通过扫描STM探针转移到绝缘态，这意味着我们可以在每个像素上记录一个比特。磁畴的最小尺寸为5 nm × 5 nm，可以实现兆位/英寸~ 2级的记录。所有写入的信息可以通过加热系统远高于T（MI）来擦除。为了进行上述探针诱导的相变，我们必须仔细控制温度。在贫硫气氛下合成的纯1 T-TaS 2晶体中，写入过程可以在更不受限制的条件下进行，例如在77 K下。晶体包括特征性的网状畴，并且不指示体金属-绝缘体转变，这表明亚稳态金属状态甚至在热力学T（MI）点以下被冻结。因此，如果能够引入更多的CDW晶格畸变，甚至在室温下也可以进行纳米级写入。

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.