Cao Ning, Hao Hua, Zheng Xiaohong, Zhang Lei, Zeng Zhi
Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China.
Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China.
Phys Chem Chem Phys. 2022 Mar 30;24(13):8032-8040. doi: 10.1039/d1cp05597f.
The destructive quantum interference (DQI) effect in molecular devices, as characterized by a sharp valley in the transmission function and conductance suppression with several orders of magnitude, is of great interest for both fundamental reasons and technical applications. Planar π conjugated systems, such as benzene, graphene molecules and graphene nanoribbons, are typical examples showing DQI and have been studied most frequently. Carbon nanotubes (CNTs) can be considered as extended planar π conjugated systems, but with a different topology from graphene. In this work, using the Hückel analytical theory, we investigated the transport properties of molecular junctions constructed with armchair CNTs which are weakly coupled to the leads with single site connections. It is found that the transport properties demonstrate obvious oscillation with a period of 3 in nanotube length as defined by the number () of atomic planes along the transport direction, which is not observed in graphene nanoribbons. Specifically, when the length is = 3 or 3 + 1, DQI will be observed at the Fermi level when both leads are connected to the same sublattice, but not observed when they are connected to different sublattices. In contrast, when the length is 3 + 2, the DQI sharp valley will never be observed at the Fermi level. Instead, a resonant peak will appear at the Fermi level when the two leads are connected to the same sublattice. Nevertheless, this resonant peak will not appear for connections with different sublattices. All these results are well explained in terms of the energy spectrum of an armchair graphene nanoribbon model and spatial distribution of the frontier molecular orbitals. The findings demonstrate the great difference between the DQI patterns of graphene nanoribbons and carbon nanotubes due to topology differences.
分子器件中的破坏性量子干涉（DQI）效应，其特征在于传输函数中的尖锐谷值以及电导抑制达几个数量级，因其基本原理和技术应用而备受关注。平面π共轭体系，如苯、石墨烯分子和石墨烯纳米带，是显示DQI的典型例子，并且研究最为频繁。碳纳米管（CNT）可被视为扩展的平面π共轭体系，但具有与石墨烯不同的拓扑结构。在这项工作中，我们使用休克尔解析理论研究了由扶手椅型碳纳米管构建的分子结的输运性质，这些碳纳米管通过单位点连接与电极弱耦合。结果发现，输运性质表现出明显的振荡，其周期为3，以沿输运方向的原子平面数（）定义的纳米管长度为周期，这在石墨烯纳米带中未观察到。具体而言，当长度为 = 3或3 + 1时，当两个电极连接到同一子晶格时，在费米能级处将观察到DQI，但当它们连接到不同子晶格时则未观察到。相反，当长度为3 + 2时，在费米能级处永远不会观察到DQI尖锐谷值。取而代之的是，当两个电极连接到同一子晶格时，在费米能级处会出现一个共振峰。然而，对于连接到不同子晶格的情况，这个共振峰不会出现。所有这些结果都根据扶手椅型石墨烯纳米带模型的能谱和前沿分子轨道的空间分布得到了很好的解释。这些发现表明，由于拓扑结构的差异，石墨烯纳米带和碳纳米管的DQI模式存在很大差异。
