Theoretical Study on the Electronic States of Layered Fluorinated Carbon Materials

我们使用第一性原理分子动力学方法从理论上研究了氟化石墨和氟化硼氮化物，并阐明了层状石墨和相关材料的叠层可以用作1）通过改变组成来控制带隙的宽禁带半导体的合成方法和2）纳米尺度磁体的合成方法。本课题的主要研究成果如下：1.氟化石墨C_nF是一种层状材料，其结构被认为是表面氟化的超薄金刚石膜的堆叠。当n= 1、2、3时，材料具有直接间隙，而如果n超过4，则差距变为间接间隙。提出了该材料可用于制作半导体激光器等光学器件，并从理论上确定了预期输出波长。我们提出，该材料是作为一个天然的超晶格合成和估计的电子和空穴在这个二维电子系统的能级。对（BN）_nF的稳定性和特性进行了理论预测.提出了一种从纳米石墨和有限长的纳米管制备磁性纳米石墨的方法。从理论上证明了纳米石墨中磁性的存在。此外，它是可控的化学处理，包括氢化，煅烧和氧取代的锯齿状纳米石墨在纳米尺度。这是对无磁性元素磁性材料合成方法的理论预测.包括关联效应在内的第一性原理电子结构计算取得了新的进展。我们提出了Kohn-Sham方程的一个推广。实现了互相关法的加速。

We theoretically investigated fluorinated graphite and fluorinated boron-nitrides using the first-principles molecular-dynamics method and clarified that the fluorination of layered graphite and related materials can be utilized as 1) a synthesis method of a wide-gap semiconductor whose band gap is controllable by changing composition and 2) a synthesis method of a nanometer-scale magnet. Major results of our project are summarized as follows.1. Fluorinated graphite C_nF is a layered material whose structure is regarded as a stacking of ultra-thin diamond films with fluorinated surfaces. The material has a direct gap when n=l,2,3, while the gap becomes indirect if n exceeds 4. We proposed that the material may be utilized for fabrication of optical devices including semiconductor LASER and determined wavelengths of expected output theoretically. We proposed that the material is synthesized as a natural superlattice and estimated energy levels of electrons and holes in this 2-dimensional electronic system. Stability and characteristics of (BN)_nF are theoretically predicted.2. We proposed a way to obtain magnetic nanographite from nanometer-scale graphite and finite nanotubes. Existence of magnetism in nanographite, which has been expected by several authors, is shown theoretically. Moreover, it is controllable by chemical treatments including hydrogenation, fluorination and oxygen-substitution of zigzag-edged nanographite in nanometer scale. This is a theoretical prediction of synthesis methods of magnetic materials without magnetic elements.3. New developments in the first-principles electronic-structure calculations including correlation effects were achieved. We proposed an extension of the Kohn-Sham equation. Acceleration of the trans-correlated method is realized.