Fundamental Studies of Development of Quasicrystalline Semiconducting Films

所取得的主要结果总结如下1。采用机械合金化技术确定了Al-Mg-Zn、Al-Mg-Cu、Al-Mg-Ag、Al-Mg-Pd和Mg-Ga-Zn五个体系准晶和近似相的稳定组成范围。当电子浓度在2.15<e/a<2.20范围内，Mg含量略高于近似相时，可以形成稳定的准晶。在Al-Mg-Zn、Al-Mg-Cu、Al-Mg-Pd、Al-Mg-Pd、Al-Cu-Ru和Al-Pd-Re中分别制备了rt型和ml型准晶。用XPS、SXS和电子比热测量对其价带结构进行了研究。发现除了在rt型准晶体中存在费米能级附近的赝隙外，价带结构都可以用自由电子图来描述。ml型准晶体的d能带广泛分布于价带能范围内，Al-3p电子分布与纯Al中自由电子的分布有严重的畸变，因此，与自由电子类rt型准晶体相比，ml型准晶体的态尖密度增大。上述测量所观察到的Ml-型和rt -型准晶体的价带结构特征反映在电子输运性质上。电导率和电子比热系数都可以用由霍尔系数推导出的载流子浓度来很好地描述，无论涉及的是ml型还是rt型。由此我们得出结论，在大多数准晶体中，电子或空穴在费米能级上占主导地位。采用激光研磨法制备了Al-Od-Mn薄膜。

Major results obtained are summarized below.1. The stable composition range of quasicrystalline and approximant phases has been determined in the totally five systems Al-Mg-Zn, Al-Mg-Cu, Al-Mg-Ag, Al-Mg-Pd and Mg-Ga-Zn by using mechanical alloying technique. It is found that the stable quasicrystal is formed when the special condition is fulfillled : the electron concentration is in the range 2.15<e/a<2.20 and the Mg content slightly higher than that of the approximant phase.2. Both RT-and Ml-type quasicrystals have been prepared by liquid quenching technique in the Al-Mg-Zn, Al-Mg-Cu and Al-Mg-Pd and Al-Mg-Pd, Al-Cu-Ru and Al-Pd-Re, respectively. The valence band structure has been studied by XPS, SXS and electronic specific heat measurements. It is found that the valence band structure is described by the free electron picture except for the presence of the pseudogap near the fermi level in the RT-type quasicrystals. The d-band in the Ml-type quasicrystals is widely spread over the valence band energy range and the Al-3p electron distribution is heavily distorted from the free electron-ike one observed in pure Al. As a result, the spiky density of states is sharpened in the Ml-type quasicrystals as compared with the free electron-like RT-type quasicrystals.3. The characteristic features of the valence band structure for Ml- and RT-type quasictystals observed by the above measurements have been reflected in the electron transport properties. The conductivity and electronic specific heat coefficient have been well described by the carrier concentration deduced from the Hall coefficient, regardless of whether Ml-or RT-types are involved. From this we conclude that either electrons or holes dominate at the Femi level in most quasicrystals.4. We could successfully synthesize the Al-Od-Mn thin films by laser abration method.