Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA.
Smalley-Curl Institute and Department of Physics and Astronomy, Rice University, Houston, TX, USA.
Nature. 2019 Aug;572(7771):628-633. doi: 10.1038/s41586-019-1420-z. Epub 2019 Jul 17.
Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction, light emission, thermoelectric energy conversion, quantum interference, heat dissipation and electronic noise at atomic and molecular scales. However, a key quantity of current interest-the thermal conductance of single-molecule junctions-has not yet been directly experimentally determined, owing to the challenge of detecting minute heat currents at the picowatt level. Here we show that picowatt-resolution scanning probes previously developed to study the thermal conductance of single-metal-atom junctions, when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, also allow quantification of the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au-alkanedithiol-Au junctions containing two to ten carbon atoms confirm that thermal conductance is to a first approximation independent of molecular length, consistent with detailed ab initio simulations. We anticipate that our approach will enable systematic exploration of thermal transport in many other one-dimensional systems, such as short molecules and polymer chains, for which computational predictions of thermal conductance have remained experimentally inaccessible.
单分子结被广泛用于探测各种性质，从原子和分子尺度上的电传导、发光、热电能量转换、量子干涉、热耗散和电子噪声等。然而，由于在皮瓦级探测微小热流的挑战，单分子结的热导这一当前热点量尚未被直接实验确定。在这里，我们展示了以前为研究单金属原子结的热导而开发的皮瓦分辨率扫描探针，当与时间平均测量方案结合使用以提高信噪比时，也可以定量测量单分子结低得多的热导。我们在含有两个到十个碳原子的典型 Au-alkanedithiol-Au 结上的实验证实，热导在第一近似上与分子长度无关，与详细的从头算模拟一致。我们预计，我们的方法将能够系统地探索许多其他一维系统中的热输运，例如短分子和聚合物链，对于这些系统，热导的计算预测在实验上仍然无法实现。
