Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Nature. 2013 Jun 13;498(7453):209-12. doi: 10.1038/nature12183.
Atomic and single-molecule junctions represent the ultimate limit to the miniaturization of electrical circuits. They are also ideal platforms for testing quantum transport theories that are required to describe charge and energy transfer in novel functional nanometre-scale devices. Recent work has successfully probed electric and thermoelectric phenomena in atomic-scale junctions. However, heat dissipation and transport in atomic-scale devices remain poorly characterized owing to experimental challenges. Here we use custom-fabricated scanning probes with integrated nanoscale thermocouples to investigate heat dissipation in the electrodes of single-molecule ('molecular') junctions. We find that if the junctions have transmission characteristics that are strongly energy dependent, this heat dissipation is asymmetric--that is, unequal between the electrodes--and also dependent on both the bias polarity and the identity of the majority charge carriers (electrons versus holes). In contrast, junctions consisting of only a few gold atoms ('atomic junctions') whose transmission characteristics show weak energy dependence do not exhibit appreciable asymmetry. Our results unambiguously relate the electronic transmission characteristics of atomic-scale junctions to their heat dissipation properties, establishing a framework for understanding heat dissipation in a range of mesoscopic systems where transport is elastic--that is, without exchange of energy in the contact region. We anticipate that the techniques established here will enable the study of Peltier effects at the atomic scale, a field that has been barely explored experimentally despite interesting theoretical predictions. Furthermore, the experimental advances described here are also expected to enable the study of heat transport in atomic and molecular junctions--an important and challenging scientific and technological goal that has remained elusive.
原子和单分子结代表了电路微型化的极限。它们也是测试量子输运理论的理想平台，这些理论是描述新型功能纳米尺度器件中电荷和能量转移所必需的。最近的工作已经成功地探测了原子尺度结中的电和热电现象。然而，由于实验挑战，原子尺度器件中的热耗散和输运仍然没有得到很好的描述。在这里，我们使用带有集成纳米热电偶的定制扫描探针来研究单分子（“分子”）结中电极的热耗散。我们发现，如果结的传输特性强烈依赖于能量，那么这种热耗散就是不对称的，即电极之间不相等，并且还取决于偏置极性和多数载流子（电子与空穴）的身份。相比之下，由仅包含几个金原子（“原子结”）组成的结，其传输特性显示出较弱的能量依赖性，不会表现出明显的不对称性。我们的结果明确地将原子尺度结的电子传输特性与其热耗散特性联系起来，为理解一系列弹性输运（即在接触区域不交换能量）的介观系统中的热耗散提供了一个框架。我们预计，这里建立的技术将能够在原子尺度上研究珀耳帖效应，尽管理论预测很有趣，但该领域在实验上几乎没有得到探索。此外，这里描述的实验进展也有望能够研究原子和分子结中的热输运，这是一个重要而具有挑战性的科学和技术目标，一直难以实现。
