Efficient long-range charge transport is required for high-performance molecular electronic devices. Resonant transport is thought to occur in single molecule junctions when molecular frontier orbital energy levels align with electrode Fermi levels, thereby enabling efficient transport without molecular or environmental relaxation. Despite recent progress, we lack a systematic understanding of the transition between nonresonant and resonant transport for molecular junctions with different chemical compositions. In this work, we show that molecular junctions undergo a reversible transition from nonresonant tunneling to resonant transport as a function of applied bias. Transient bias-switching experiments show that the nonresonant to resonant transition is reversible with the applied bias. We determine a general quantitative relationship that describes the transition voltage as a function of the molecular frontier orbital energies and electrode Fermi levels. Overall, this work highlights the importance of frontier orbital energy alignment in achieving efficient charge transport in molecular devices.

中文翻译：

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分子结中非共振和共振电荷传输之间的转换

高性能分子电子器件需要高效的远程电荷传输。当分子前沿轨道能级与电极费米能级对齐​​时，共振传输被认为发生在单分子结中，从而实现有效传输而不会发生分子或环境松弛。尽管最近取得了进展，但我们对具有不同化学成分的分子连接的非共振和共振传输之间的转变缺乏系统的理解。在这项工作中，我们表明分子结经历了从非共振隧穿到共振传输的可逆转变，作为施加偏置的函数。瞬态偏置切换实验表明，非谐振到谐振的转变随着施加的偏置是可逆的。我们确定了一个一般的定量关系，该关系将跃迁电压描述为分子前沿轨道能量和电极费米能级的函数。总的来说，这项工作强调了前沿轨道能量排列在分子器件中实现有效电荷传输的重要性。