HOMO Level Pinning in Molecular Junctions: Joint Theoretical and Experimental Evidence
HOMO Level Pinning in Molecular Junctions: Joint Theoretical and Experimental Evidence
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DOI：
10.1021/acs.jpclett.8b00575
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发表时间：
2018-05-03
影响因子：
5.7
通讯作者：
Cornil, J.
中科院分区：
文献类型：
--
作者：
Rodriguez-Gonzalez, S.;Xie, Z.;Cornil, J.
为了构建功能器件，分子电子学的一个中心问题是评估一旦分子插入分子结中，通过化学衍生化分离的化合物的电子结构的变化是否被保留。最近的理论研究表明，这并不总是由于钉扎效应的发生，使对齐的运输水平不敏感的孤立系统的电子结构的变化的情况下。我们在这里探索这种现象，通过调查在实验和理论水平的I/V特性的分子结，将三个不同的三环亚苯基乙炔基衍生物的设计表现出显着的变化的HOMO水平在隔离状态。在理论水平上，我们的NEGF/DFT计算包括三种化合物的结上进行的显示，而分子的HOMO变化0.61 eV的隔离状态下，其相对于结中的金电极的费米能级的对齐是非常相似的（在0.1 eV内）。在实验水平上，由三种化合物制成的自组装膜已被导电AFM探针接触，以测量它们的I/V特性。通过拟合I/V曲线，使用基于单能级描述的模型（Newns-Anderson模型），推导出HOMO相对于金电极费米能级的对准。提取的值被发现是非常相似的三个衍生物，在完全符合理论预测，从而提供了明确的证据HOMO能级钉扎效应。
A central issue in molecular electronics in order to build functional devices is to assess whether changes in the electronic structure of isolated compounds by chemical derivatization are retained once the molecules are inserted into molecular junctions. Recent theoretical studies have suggested that this is not always the case due to the occurrence of pinning effects making the alignment of the transporting levels insensitive to the changes in the electronic structure of the isolated systems. We explore here this phenomenon by investigating at both the experimental and theoretical levels the I/V characteristics of molecular junctions incorporating three different three-ring phenylene ethynylene derivatives designed to exhibit a significant variation of the HOMO level in the isolated state. At the theoretical level, our NEGF/DFT calculations performed on junctions including the three compounds show that, whereas the HOMO of the molecules varies by 0.61 eV in the isolated state, their alignment with respect to the Fermi level of the gold electrodes in the junction is very similar (within 0.1 eV). At the experimental level, the SAMs made of the three compounds have been contacted by a conducting AFM probe to measure their I/V characteristics. The alignment of the HOMO with respect to the Fermi level of the gold electrodes has been deduced by fitting the I/V curves, using a model based on a single-level description (Newns-Anderson model). The extracted values are found to be very similar for the three derivatives, in full consistency with the theoretical predictions, thus providing clear evidence for a HOMO level pinning effect.