Theoretical Study on the Electronic States of Layered Fluorinated Carbon Materials

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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.