以時間相關密度泛函理論研究新興二維材料之電漿子激發

Abstract

石墨烯是由碳原子以sp2混成軌域所組成的六角型呈蜂巢晶格的平面薄膜，其電阻率極低，因此可望用來製造導電速度更快的電子元件，是近年來備受矚目的新興材料。 藉由引入庫倫位能阻斷的修正，以及更精確的動量解析度後，我們利用時間相關密度泛函理論計算石墨烯在倒晶格空間中不同方向的電子能量損失譜，我們發現石墨烯的 π 電漿子呈現根號q的色散關係，即電漿子能量正比於動量開根號，此結果不同於先前預測由二維狄拉克電漿子所造成的線性色散關係。此外我們也藉由計算在倒晶格空間中不同方向的電子能量損失譜，探討石墨烯在倒晶格空間的非等方向性。 我們也利用時間相關密度泛函理論計算數種二維材料 (二維六方氮化硼、單層二硒化鉭) 在倒晶格空間中不同方向的電子能量損失譜，探討其在倒晶格空間的的非等方向性，以及電漿子的色散關係。

Graphene is one of the most popular materials in recent years. It is composed of a single-atom-thick hexagonal lattice of sp2-bonded carbon atoms. Its resistivity is extremely low so that it is expected to produce electric devices of which electric conductivity is better than that of currently existing electric devices. With the exact Coulomb cutoff technique and a better momentum q resolution, we perform time-dependent density-functional theory calculations to study electron energy loss spectra for graphene in reciprocal space. We find that the dispersion relation of π- plasmon shows a square root q dispersion, being opposite to previous studies which reported a linear q dispersion resulted from two-dimensional Dirac plasmon. Furthermore, we also investigate the electronic anisotropy of graphene by calculating electron energy loss spectra in different directions in reciprocal space. We also use the time-dependent density-functional theory to calculate electron energy loss spectra for other emergent layered materials, namely, the boron nitride monolayer and the 2H-TaSe2 monolayer to discuss electronic anisotropy and dispersion relation of plasmon.