STM and STS studies of atomic structure and electronic states in quasicrystals

为了研究准晶体中的原子结构和电子态，我们进行了以下实验。对于用Czochralski法生长的AL-Ni-Co体系中的单晶十方准晶，进行了STM观察和隧道光谱分析。通过STM观察到：1)原子排列的准周期性非常完美；2)两种准周期层之间的10_5螺旋关系；3)表面重构的原子沿十倍方向排列具有多种周期性；4)极低密度的pason缺陷。特别是，结果iv)提出了任何相位缺陷的STM观察的第一个例子。通过隧道光谱，我们发现了几个与表面态相对应的峰。根据结果iv)，我们利用高温原位HRTEM研究了准晶中的相弛豫过程。我们使用的样品是Al-Cu-Co十方准晶体。首先，我们引入了820℃退火的均匀相位应变。然后，我们将温度提高到850℃，观察相弛豫过程。结果表明，随着相应变均匀区和无相区边界的移动，相松弛发生。在此过程中，相位应变均匀区域的相位位移保持不变，平铺始终在边界上连续进行。

For the purpose of investigating atomic structure and electronic states In quasicrystals, we performed the following experiments. For a single-grained decagonal quasicrystal in the AL-Ni-Co system grown by Czochralski method, STM observations and tunneling spectroscopy were done. By STM the followings were observed: i)high perfection in the quasiperiodicity in the atomic arrangement, ii)10_5screw relation between the two kinds of quasiperiodic layers, iii)various periodicities in the atomic arrangement along the tenfold direction by surface reconstruction and iv) very low density of pason defects. In particular, the result iv) presents the first example of STM observation of any phason defect. By tunneling spectroscopy we found several peaks corresponding to surface states. In relation to the result iv), we investigated the phason relaxation process in quasicrystal by high-temperature in-situ HRTEM. The sample we used was an Al-Cu-Co decagonal quasicrystal. First, we introduced a uniform phason strai by 820℃ annealing. Then, we raised the temperature to 850℃ and observed the phason relaxation process. It was found that the phason relaxation proceeds with the shift of the boundary between the region with the uniform phason strain and the phason-free region. In this process the phason displacement in the region with the uniform phason strain remains unchanged and the tiling always continues coherently across the boundary.