Joule Heating in Single-Molecule Point Contacts Studied by Tip-Enhanced Raman Spectroscopy
Joule Heating in Single-Molecule Point Contacts Studied by Tip-Enhanced Raman Spectroscopy
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DOI：
10.1021/acsnano.2c05642
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发表时间：
2022-10-05
期刊：
影响因子：
17.1
通讯作者：
Kumagai, Takashi
中科院分区：
文献类型：
--
作者：
Cirera, Borja;Wolf, Martin;Kumagai, Takashi
载流分子结的加热和冷却是分子电子学中的一个重要问题。微观机理涉及复杂的因素，如能量输入，分子性质，电极材料和分子-电极耦合。为了获得深入的理解，这是一个理想的实验，以评估振动的人口，代表能量分布存储在分子内。在这里，我们展示了直接观察到的振动加热在一个单一的C60分子的尖端增强拉曼光谱（TERS）。通过TERS光谱中的反斯托克斯拉曼散射监测各个振动模式的加热。在单分子结的差距距离的精确控制，使我们能够揭示在不同的电子传输制度，即，隧道和单分子点接触（SMPC）制度的定性不同的加热机制。强焦耳加热通过非弹性电子振动散射发生在SMPC制度，而光学加热是占主导地位的隧穿制度。SMPC处的强焦耳加热也导致拉曼峰位的显著红移和线宽展宽。此外，通过检查SMPC与几种类型的接触表面，我们表明，加热效率有关的电流密度在SMPC和振动耗散通道到电极。
Heating and cooling in current-carrying molec-ular junctions is a crucial issue in molecular electronics. The microscopic mechanism involves complex factors such as energy inputs, molecular properties, electrode materials, and molecule-electrode coupling. To gain an in-depth under-standing, it is a desired experiment to assess vibrational population that represents the energy distribution stored within the molecule. Here, we demonstrate the direct observation of vibrational heating in a single C60 molecule by means of tip-enhanced Raman spectroscopy (TERS). The heating of respective vibrational modes is monitored by anti-Stokes Raman scattering in the TERS spectra. The precise control of the gap distance in the single-molecule junction allows us to reveal a qualitatively different heating mechanism in distinct electron transport regimes, namely, the tunneling and single-molecule point contact (SMPC) regimes. Strong Joule heating via inelastic electron-vibration scattering occurs in the SMPC regime, whereas optical heating is predominant in the tunneling regime. The strong Joule heating at the SMPC also leads to a pronounced red shift of the Raman peak position and line width broadening. Furthermore, by examining the SMPC with several types of contact surfaces, we show that the heating efficiency is related to the current density at the SMPC and the vibrational dissipation channels into the electrode.