分子连接中的HOMO能级固定：联合的理论和实验证据,The Journal of Physical Chemistry Letters

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分子连接中的HOMO能级固定：联合的理论和实验证据
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2018-04-16 00:00:00 , DOI: 10.1021/acs.jpclett.8b00575
S. Rodriguez-Gonzalez ₁ , Z. Xie ₂ , O. Galangau ₃ , P. Selvanathan ₃ , L. Norel ₃ , C. Van Dyck ₄ , K. Costuas ₃ , C. D. Frisbie ₂ , S. Rigaut ₃ , J. Cornil ₁

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为了构建功能器件，分子电子学中的一个中心问题是评估一旦将分子插入分子结中，通过化学衍生作用分离出的化合物的电子结构的变化是否得以保留。近期的理论研究表明，由于钉扎效应的出现，使传输能级的排列对孤立系统的电子结构的变化不敏感，因此并非总是如此。我们在这里通过在实验和理论水平上研究I / V来探索这种现象。结合了三种不同的三环亚苯基亚乙炔基衍生物的分子接合结构的特征，设计为在分离状态下显示出HOMO能级的显着变化。从理论上讲，我们对包括三种化合物的连接处进行的NEGF / DFT计算表明，尽管分子的HOMO在孤立状态下变化了0.61 eV，但它们相对于连接处金电极的费米能级排列非常相似（在0.1 eV内）。在实验水平上，由三种化合物制成的SAM已通过导电AFM探针接触以测量其I / V特性。通过拟合I推导了HOMO相对于金电极费米能级的对准/ V曲线，使用基于单级描述的模型（Newns–Anderson模型）。发现这三个导数的提取值非常相似，与理论预测完全一致，从而为HOMO水平钉扎效应提供了清晰的证据。

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HOMO Level Pinning in Molecular Junctions: Joint Theoretical and Experimental Evidence

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.

更新日期：2018-04-16

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