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Advantages and limitations of transition voltage spectroscopy: A theoretical analysis

机译：过渡电压光谱法的优缺点：理论分析

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In molecular charge transport, transition voltage spectroscopy (TVS) holds the promise that molecular energy levels can be explored at bias voltages lower than required for resonant tunneling. We investigate the theoretical basis of this tool using a generic model. In particular, we study the length dependence of the conducting frontier orbital and of the "transition voltage" as a function of length. We show that this dependence is influenced by the amount of screening of the electrons in the molecule, which determines the voltage drop at the contacts or across the entire molecule. We observe that the transition voltage depends significantly on the length, but the ratio between the transition voltage and the conducting frontier orbital is approximately constant only in strongly screening (conjugated) molecules. Uncertainty about the screening within a molecule thus limits the predictive power of TVS. We furthermore argue that the relative length independence of the transition voltage for nonconjugated chains is due to strong localization of the frontier orbitals on the end groups ensuring binding of the rods to the metallic contacts. Finally, we investigate the characteristics of TVS in asymmetric molecular junctions. If a single level dominates the transport properties, TVS can provide a good estimate for both the level position and the degree of junction asymmetry. If more levels are involved, the applicability of TVS becomes limited.
机译：在分子电荷传输中，过渡电压光谱（TVS）有望在低于共振隧穿所需的偏置电压下探索分子能级。我们使用通用模型研究此工具的理论基础。特别地，我们研究了导电边界轨道和“转变电压”的长度依赖性与长度的关系。我们表明，这种依赖性受分子中电子筛选数量的影响，这决定了触点或整个分子上的电压降。我们观察到过渡电压很大程度上取决于长度，但是过渡电压与导电前沿轨道之间的比率仅在强屏蔽（共轭）分子中近似恒定。因此，分子内筛选的不确定性限制了TVS的预测能力。我们进一步认为，非共轭链的跃迁电压的相对长度独立性是由于端基上的前沿轨道强烈定位而确保杆与金属触点的结合。最后，我们研究不对称分子结中TVS的特征。如果单个水平控制着传输特性，TVS可以为水平位置和结不对称程度提供良好的估计。如果涉及更多级别，TVS的适用性将受到限制。

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  • 来源
    《Physical review》 |2011年第11期|p.882-889|共8页
  • 作者

    F. Mirjani; J. M. Thijssen; S. J. van der Molen;

  • 作者单位

    Kavli Institute ofNanoscience, Delft University of Technology, Lorentzweg 1, NL-2628 CJ Delft, The Netherlands;

    Kavli Institute ofNanoscience, Delft University of Technology, Lorentzweg 1, NL-2628 CJ Delft, The Netherlands;

    Kamerlingh Onnes Laboratorium, Leiden University, Niels Bohrweg 2, NL-2300 RA Leiden, The Netherlands;

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