Determination of Energy Level Alignment and Coupling Strength in 4,4′-Bipyridine Single-Molecule Junctions
Determination of Energy Level Alignment and Coupling Strength in 4,4′-Bipyridine Single-Molecule Junctions
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DOI：
10.1021/nl404143v
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发表时间：
2014-02-01
期刊：
影响因子：
10.8
通讯作者：
Venkataraman, Latha
中科院分区：
文献类型：
--
作者：
Kim, Taekyeong;Darancet, Pierre;Venkataraman, Latha
我们测量了单个Au-4，4 '-bipyridine-Au结的电导和热电势，通过调节电极间距获得了不同的低电导和高电导结合几何形状。我们使用这些数据来确定这些结的电子能级排列和耦合强度，这些结已知通过最低未占分子轨道（LUMO）进行。与直觉相反，我们发现，在高电导结中，LUMO共振能量比在低电导结中更远离Au费米能量。然而，高导电结的LUMO更好地耦合到电极。这些结果与自能校正的零偏密度泛函理论计算结果吻合得很好。我们的计算结果进一步表明，测量电导和热电在胺封端的oligophenyl-Au结，其中传导发生通过最高占据的分子轨道，不能用来提取电子参数，因为它们的传输函数不遵循一个简单的洛伦兹形式。
We measure conductance and thermopower of single Au-4,4'-bipyridine-Au junctions in distinct low and high conductance binding geometries accessed by modulating the electrode separation. We use these data to determine the electronic energy level alignment and coupling strength for these junctions, which are known to conduct through the lowest unoccupied molecular orbital (LUMO). Contrary to intuition, we find that, in the high-conductance junction, the LUMO resonance energy is further away from the Au Fermi energy than in the low-conductance junction. However, the LUMO of the high-conducting junction is better coupled to the electrode. These results are in good quantitative agreement with self-energy corrected zero-bias density functional theory calculations. Our calculations show further that measurements of conductance and thermopower in amine-terminated oligophenyl-Au junctions, where conduction occurs through the highest occupied molecular orbitals, cannot be used to extract electronic parameters as their transmission functions do not follow a simple Lorentzian form.