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arXiv 1407.5250cond-mat.mes-hallcond-mat.mtrl-sci
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通过自组装单层分子结的输运:面内退相的作用

Transport Through Self-Assembled Monolayer Molecular Junctions: Role of In-Plane Dephasing

Yonatan Dubi

摘要:

自组装单层(SAM)分子结(MJs)构成了未来分子电子器件的一个有前途的候选积木。SAM-MJ的输运性质通常使用唯象的Simmons模型或全相干输运理论来计算,采用SAMs周期性。我们认为,退相起着重要的作用,在确定SAM-MJ的传输特性。我们提出了一种计算SAM-MJ输运性质的方法,该方法本质上考虑了电子运动穿过SAM平面时的面内失相。计算是基于非平衡格林函数形式主义,与本地动力学近似,描述沿SAM平面的非相干运动。我们的方法很好地描述了通过SAM-MJ运输的两个标志,即与单分子结相比,电流随分子链长度的指数衰减和每个分子的电流减少。具体而言,我们表明,失相导致的电流作为分子长度的函数的指数衰减,即使是共振隧穿,其中完全相干计算显示很少或没有长度依赖性的电流。失相也示出导致在SAM-MJ的电流相比,单分子结,在一个现实的参数制度,其中相干计算显示只有一个非常小的减少的电流大幅减少。最后,我们讨论了失相效应对更细微的输运现象,如电导奇偶效应和负微分电阻的影响。

英文摘要:

Self-assembled-monolayer (SAM) molecular junctions (MJs) constitute a promising building block candidate for future molecular electronic devices. Transport properties of SAM-MJs are usually calculate using either the phenomenological Simmons model, or a fully-coherent transport theory, employing the SAMs periodicity. We suggest that dephasing plays an important role in determining the transport properties of SAM-MJs. We present an approach for calculating the transport properties of SAM-MJs that inherently takes into account in-plane dephasing in the electron motion as it traverses the SAM plane. The calculation is based on the non-equilibrium Green's function formalism, with a local dynamics approximation that describes incoherent motion along the SAM plane. Our approach describes well the two hallmarks of transport through SAM-MJs, namely the exponential decay of current with molecular chain length and the reduction of the current per molecule as compared to single-molecule junctions. Specifically, we show that dephasing leads to an exponential decay of the current as a function of molecular length, even for resonant tunneling, where the fully coherent calculation shows little or no length-dependence of the current. The dephasing is also shown to lead to a substantial reduction of the current in a SAM-MJ as compared to the single molecule junction, in a realistic parameter regime, where the coherent calculation shows only a very small reduction of the current. Finally, we discuss the effect of dephasing on more subtle transport phenomena such as the conductance even-odd effect and negative differential resistance.

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