Dependence of single-molecule junction conductance on molecular conformation
Dependence of single-molecule junction conductance on molecular conformation
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DOI：
10.1038/nature05037
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发表时间：
2006-08-24
期刊：
影响因子：
64.8
通讯作者：
Steigerwald, Michael L.
中科院分区：
文献类型：
--
作者：
Venkataraman, Latha;Klare, Jennifer E.;Steigerwald, Michael L.
自从首次提出（1）单个分子可以作为活性电子元件起作用以来，已经开发了许多技术来测量单个分子的电荷传输特性（2-12）。虽然在高真空条件下的扫描隧道显微镜观察可以允许稳定的测量电子输运，大多数测量的金属-分子-金属结中结合的单个分子表现出相对较大的电导变化。因此，即使是关于分子在这种连接中如何行为的简单预测也没有得到严格的检验。例如，众所周知（13，14），通过分子的隧穿电流取决于其构象;但是，尽管一些实验已经验证了这种效应（15-18），但还没有关于结电导如何随分子构象变化的全面映射。在联苯的简单情况下-具有由单个C-C键连接的两个苯环的分子-电导预计随着两个环之间的相对扭转角而变化，其中平面构象具有最高的电导。在这里，我们使用胺连接基团来形成具有更可再现的电流-电压特性的单分子结（19）。这使我们能够提取平均电导值从一系列的七个联苯分子与不同的环取代，改变分子的扭转角的数千个单独的测量。我们发现，该系列的电导随着扭转角的增加而降低，与预测的通过π-共轭联苯系统的传输的余弦平方关系一致（13）。
Since it was first suggested(1) that a single molecule might function as an active electronic component, a number of techniques have been developed to measure the charge transport properties of single molecules(2-12). Although scanning tunnelling microscopy observations under high vacuum conditions can allow stable measurements of electron transport, most measurements of a single molecule bonded in a metal - molecule - metal junction exhibit relatively large variations in conductance. As a result, even simple predictions about how molecules behave in such junctions have still not been rigorously tested. For instance, it is well known(13,14) that the tunnelling current passing through a molecule depends on its conformation; but although some experiments have verified this effect(15-18), a comprehensive mapping of how junction conductance changes with molecular conformation is not yet available. In the simple case of a biphenyl - a molecule with two phenyl rings linked by a single C - C bond - conductance is expected to change with the relative twist angle between the two rings, with the planar conformation having the highest conductance. Here we use amine link groups to form single-molecule junctions with more reproducible current - voltage characteristics(19). This allows us to extract average conductance values from thousands of individual measurements on a series of seven biphenyl molecules with different ring substitutions that alter the twist angle of the molecules. We find that the conductance for the series decreases with increasing twist angle, consistent with a cosine-squared relation predicted for transport through pi-conjugated biphenyl systems(13).