Laboratoire de Chimie, Ecole Normale Supérieure de Lyon, Université de Lyon, CNRS, France.
Nanotechnology. 2012 Aug 10;23(31):315702. doi: 10.1088/0957-4484/23/31/315702. Epub 2012 Jul 13.
Low sensitivity is a key problem in inelastic electron tunneling spectroscopy (IETS) with the scanning tunneling microscope. Using first-principles simulations, we predict different means to tune the IETS sensitivity of symmetrical functional aromatics on a Cu(111) surface. We show how the IET-spectra of phenyl-NO₂ compounds can be greatly enhanced as compared to pristine phenyl. More precisely, the NO₂ substituent qualifies as a sensitizer of low-frequency wagging modes, but also as a quencher of high-frequency stretching modes. At variance, the CO₂ substituent is found to suppress the whole IET-activity. The head-up (non-anchoring) and head-down (anchoring) configurations of the functional group lead to minor changes in the signals, nevertheless allowing access to discriminate configurational features. It is shown how to disentangle the electronic and steric effects of the substituent in the STM junction.
低灵敏度是扫描隧道显微镜中的非弹性电子隧道谱（IETS）的一个关键问题。我们使用第一性原理模拟，预测了在 Cu(111)表面上调节对称官能芳烃的 IETS 灵敏度的不同方法。我们展示了与原始苯相比，苯基-NO₂化合物的 IET 谱可以大大增强。更准确地说，NO₂取代基可以作为低频摇摆模式的敏化剂，但也可以作为高频伸缩模式的猝灭剂。相比之下，CO₂取代基被发现抑制了整个 IET 活性。官能团的头向上（非锚固）和头向下（锚固）构型只会导致信号的微小变化，但仍然允许区分构型特征。我们展示了如何在 STM 结中分解取代基的电子和空间效应。
