摘要:
运用基于密度泛函理论的第一性原理方法,系统研究了小尺寸锐钛矿相(n,0)型TiO2纳米管(D <16?)的几何构型、电子结构和光学性质。结果表明：随着管径增大,体系单位TiO2分子的形成能降低,体系趋于稳定；在管径14?左右,(n,0)型TiO2纳米管会发生一次构型的转变。能带分析显示, TiO2纳米管的电子态比较局域化,小管径下(D<14?)其导电性更好；随着构型的转变, TiO2纳米管由直接带隙转变为间接带隙,并且带隙值随着管径的增大而增大,这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果。两种效应的竞争,使得TiO2纳米管的介电函数虚部ε2(ω)谱的峰值位置随管径增大既可能红移也可能蓝移,管径大于9?(即(8,0)管)之后, TiO2纳米管的光吸收会出现明显的增强。
Abstract:
Using first-principles calculations based on the density functional theory, we systematically study the geometry structure, electronic structure and optical properties of the small size (n, 0)-type TiO2 nanotubes (D <16 ?) derived from anatase. The calculation results indicate that the formation energy of each TiO2 unit decreases with the diameter increasing, and the nanotubes become more stable. At a diameter of about 14 ?, a configuration change occurs. Band structure analysis shows that electronic states of TiO2 nanotubes are localized, and the conductivity is better for nanotubes with small diameters (D <14 ?). According to the configuration change, TiO2 nanotubes shift from direct band gap to indirect band gap. And the band gap increases with diameter increasing, because π orbital overlap effect is greater than the quantum confinement effect. Owing to the competition between the two effects, the peaks of the dielectric function ε2(ω) will become redshifted or blueshifted. When its diameter is larger than 9 ? ((8, 0) tube), the optical absorption of TiO2 nanotubes will be significantly enhanced.
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