Tarakeshwar P, Kim Dae M
J Phys Chem B. 2005 Apr 28;109(16):7601-4. doi: 10.1021/jp050525j.
Examined in this paper is the role of the metal electrode influencing the structure and electronic properties of semiconducting carbon nanotubes near the interface at low bias. Specifically, we present quantum-chemical calculations of finite sections of a (8,0) semiconducting single wall nanotube contacted with gold and palladium clusters. The calculations at the density functional level of theory, which included full geometry optimizations, indicate the formation of bonds between the metal atoms of the electrode and the carbon atoms of the nanotube. The local work function of the metal electrode can be expected to exhibit significant variations as a result of this bond formation. Compared to the gold-contacted nanotubes, the palladium-contacted nanotubes have a small but interesting increase in both length and diameter. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the gold-contacted nanotube are shown localized at the edges. In contrast, the HOMO and LUMO of the palladium-contacted nanotube are extended over the entire nanotube and the metal cluster contacted to it, providing thereby a better conduction path in the contact region of the electrode and the nanotube. The involvement of the highly directional d orbitals in the interactions involving the palladium cluster leads to an enhanced pi electron density in the nanotube. This enhanced pi electron density is synonymous with an improved electron transmission.
本文研究了金属电极在低偏压下对界面附近半导体碳纳米管结构和电子性质的影响。具体而言，我们给出了与金和钯团簇接触的(8,0)半导体单壁纳米管有限截面的量子化学计算结果。在密度泛函理论水平上进行的计算（包括完全几何优化）表明，电极的金属原子与纳米管的碳原子之间形成了化学键。由于这种化学键的形成，预计金属电极的局部功函数会出现显著变化。与金接触的纳米管相比，钯接触的纳米管在长度和直径上都有小但有趣的增加。金接触纳米管的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）显示定域在边缘。相比之下，钯接触纳米管的HOMO和LUMO扩展到整个纳米管及其接触的金属团簇上，从而在电极与纳米管的接触区域提供了更好的传导路径。高度定向的d轨道参与涉及钯团簇的相互作用，导致纳米管中的π电子密度增强。这种增强的π电子密度等同于改善的电子传输。
