Stretching-Induced Conductance Variations as Fingerprints of Contact Configurations in Single-Molecule Junctions
Stretching-Induced Conductance Variations as Fingerprints of Contact Configurations in Single-Molecule Junctions
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DOI：
10.1021/jacs.7b03393
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发表时间：
2017-06-21
影响因子：
15
通讯作者：
Kawai, Tomoji
中科院分区：
文献类型：
--
作者：
Kim, Yong-Hoon;Kim, Hu Sung;Kawai, Tomoji
分子-电极接触原子结构是表征分子器件的关键因素，但对它们的准确理解和控制仍然难以捉摸。基于第一性原理计算和单分子断裂结实验，我们证明了二硫代烷基结的电导随机械拉伸而增大或减小，具体趋势由S-Au键配位数(Cn)或分子-电极接触原子结构决定。具体地，我们发现机械拉伸导致了基于S-Au-CN2和CN3接触的结的电导增加，而对于具有CN1接触的结的电导受拉伸的影响很小，当形成Au单原子链时，电导下降。详细的分析揭示了在不同接触CN情况下，拉伸引起的最高占据轨道相关态向电极的费米能级上移和分子电极电子耦合劣化之间的竞争机制。此外，我们在实验上发现在较快的伸长速度下有更高的机会观察到电导增强模式，这可以用从头算分子动力学模拟来解释，该模拟揭示了热涨落在帮助接触变形到包括单原子Au链的低配位组态中的重要作用。指出了以往将电导直方图中的峰值与特定的接触原子结构联系起来的不足，解决了S-Au基单分子结中普遍存在的多个电导峰的起源之争。
Molecule-electrode contact atomic structures are a critical 2 factor that characterizes molecular devices, but their precise understanding and control still remain elusive. Based on combined first-principles calculations and single-molecule break junction experiments, we herein establish that the conductance of alkanedithiolate junctions can both increase and decrease with mechanical stretching, and the specific trend is determined by the S-Au linkage coordination number (CN) or the molecule-electrode contact atomic structure. Specifically, we find that the mechanical pulling results in the conductance increase for the junctions based on S-Au CN two and CN three contacts, while the conductance is minimally affected by stretching for junctions with the CN one contact and decreases upon the formation of Au monatomic chains. Detailed analysis unravels the mechanisms involving the competition between the stretching-induced upshift of the highest occupied molecular orbital related states toward the Fermi level of electrodes and the deterioration of molecule electrode electronic couplings in different contact CN cases. Moreover, we experimentally find a higher chance to observe the conductance enhancement mode under a faster elongation speed, which is explained by ab initio molecular dynamics simulations that reveal an important role of thermal fluctuations in aiding deformations of contacts into low-coordination configurations that include monatomic Au chains. Pointing out the insufficiency in previous notions of associating peak values in conductance histograms with specific contact atomic structures, this work resolves the controversy on the origins of ubiquitous multiple conductance peaks in S-Au-based single molecule junctions.