Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions,The Journal of Physical Chemistry C

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Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2017-06-27 00:00:00 , DOI: 10.1021/acs.jpcc.7b03853
Yanxi Zhang _{1,

2} , Xinkai Qiu _{1,

2} , Pavlo Gordiichuk ₂ , Saurabh Soni _{1,

2} , Theodorus L. Krijger _{1,

2} , Andreas Herrmann ₂ , Ryan C. Chiechi _{1,

2}

Affiliation

This paper examines the relationship between mechanical deformation and the electronic properties of self-assembled monolayers (SAMs) of the oligothiophene 4-([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)butane-1-thiol (T4C4) in tunneling junctions using conductive probe atomic force microscopy (CP-AFM) and eutectic Ga–In (EGaIn). We compared shifts in conductivity, transition voltages of T4C4 with increasing AFM tip loading force to alkanethiolates. While these shifts result from an increasing tilt angle from penetration of the SAM by the AFM tip for the latter, we ascribe them to distortions of the π system present in T4C4, which is more mechanically robust than alkanethiolates of comparable length; SAMs comprising T4C4 shows about five times higher Young’s modulus than alkanethiolates. Density functional theory calculations confirm that mechanical deformations shift the barrier height due to changes in the frontier orbitals caused by small rearrangements to the conformation of the quaterthiophene moiety. The mechanical robustness of T4C4 manifests as an increased tolerance to high bias in large-area EGaIn junctions suggesting that electrostatic pressure plays a significant role in the shorting of molecular junctions at high bias.

中文翻译：

机械和电气坚固的自组装单层膜，适用于大面积隧道结。

本文研究了低聚噻吩4-（[[2,2'：5'，2″：5″，2‴-四噻吩] -5-yl的自组装单层（SAMs）的机械变形与电子性质之间的关系。）丁烷-1-硫醇（T4C4）在隧道结中使用导电探针原子力显微镜（CP-AFM）和共晶Ga-In（EGaIn）。我们比较了电导率的变化，T4C4的跃迁电压与硫代烷烃的AFM尖端加载力的增加。尽管这些偏移是由于AFM针尖穿透SAM而导致的SAM倾斜角增加而引起的，但我们将它们归因于T4C4中存在的π系统畸变，其机械强度比同等长度的链烷硫醇更强。包含T4C4的SAM显示出的杨氏模量比链烷硫醇盐高约五倍。密度泛函理论计算证实，由于四重噻吩部分构象的微小重排导致边界轨道发生变化，机械变形使势垒高度发生了变化。T4C4的机械强度表现为在大面积EGaIn结中对高偏压的耐受性增强，这表明静电压力在高偏压下缩短分子结的过程中起着重要作用。

更新日期：2017-06-28

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