Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
J Am Chem Soc. 2012 Jul 25;134(29):12072-82. doi: 10.1021/ja302602b. Epub 2012 Jul 12.
Construction of permanent metal-molecule-metal (MMM) junctions, though technically challenging, is desirable for both fundamental investigations and applications of molecule-based electronics. In this study, we employed the nanotransfer printing (nTP) technique using perfluoropolyether (PFPE) stamps to print Au thin films onto self-assembled monolayers (SAMs) of alkanedithiol formed on Au thin films. We show that the resulting MMM junctions form permanent and symmetrical tunnel junctions, without the need for an additional protection layer between the top metal electrode and the molecular layer. This type of junction makes it possible for direct investigations into the electrical properties of the molecules and the metal-molecule interfaces. Dependence of transport properties on the length of the alkane molecules and the area of the printed Au electrodes has been examined systematically. From the analysis of the current-voltage (I-V) curves using the Simmons model, the height of tunneling barrier associated with the molecule (alkane) has been determined to be 3.5 ± 0.2 eV, while the analysis yielded an upper bound of 2.4 eV for the counterpart at the interface (thiol). The former is consistent with the theoretical value of ~3.5-5.0 eV. The measured I-V curves show scaling with respect to the printed Au electrode area with lateral dimensions ranging from 80 nm to 7 μm. These results demonstrate that PFPE-assisted nTP is a promising technique for producing potentially scalable and permanent MMM junctions. They also demonstrate that MMM structures (produced by the unique PFPE-assisted nTP) constitute a reliable test bed for exploring molecule-based electronics.
构建永久性的金属-分子-金属（MMM）结，尽管在技术上具有挑战性，但对于基于分子的电子学的基础研究和应用都是理想的。在这项研究中，我们使用全氟聚醚（PFPE）印章的纳米转移印刷（nTP）技术，将 Au 薄膜印刷到自组装单层（SAM）上烷二硫醇形成的 Au 薄膜上。我们表明，所得的 MMM 结形成了永久性和对称的隧道结，而不需要在顶部金属电极和分子层之间添加额外的保护层。这种类型的结使得可以直接研究分子和金属-分子界面的电特性。已经系统地研究了输运性质对烷烃分子长度和印刷 Au 电极面积的依赖性。通过使用 Simmons 模型对电流-电压（I-V）曲线进行分析，确定与分子（烷烃）相关的隧道势垒高度为 3.5±0.2 eV，而分析得出界面处的对应物（硫醇）的上限为 2.4 eV。前者与理论值~3.5-5.0 eV 一致。测量的 I-V 曲线显示出与印刷 Au 电极面积的比例关系，其横向尺寸范围从 80nm 到 7μm。这些结果表明，PFPE 辅助 nTP 是一种有前途的技术，可用于制造潜在可扩展和永久性的 MMM 结。它们还表明，MMM 结构（由独特的 PFPE 辅助 nTP 产生）构成了探索基于分子的电子学的可靠测试平台。
