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

为了研究准晶中的原子结构和电子态，我们进行了以下实验。对提拉法生长的Al-Ni-Co系单晶十方准晶进行了扫描隧道显微镜观察和隧道光谱研究。用扫描隧道显微镜观察到：1)原子排列的高度周期性，2)两种准周期层之间的10~5螺旋关系，3)表面重构的原子排列具有不同的周期性，4)很低的Pason缺陷密度。特别地，结果IV)给出了任何相子缺陷的扫描隧道显微镜观察的第一个例子。通过隧道光谱，我们发现了几个与表面态相对应的峰。结合结果IV)，我们用高温原位高分辨电子显微镜研究了准晶中的相子弛豫过程。我们使用的样品是Al-Cu-Co十方准晶。首先，我们介绍了一种由820℃退火而成的均匀相干态。然后，我们将温度升高到850℃，观察到了相子弛豫过程。结果表明，随着均匀相干应变区和无相干区边界的移动，相子弛豫过程也随之发生。在这个过程中，具有均匀相位子应变的区域中的相位子位移保持不变，而拼贴总是在边界上相干地继续进行。

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.