Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
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通过等离子体增强拉曼散射对单分子进行化学测绘
DOI：
10.1038/nature12151
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发表时间：
2013-06-06
期刊：
影响因子：
64.8
通讯作者：
Hou, J. G.
中科院分区：
文献类型：
--
作者：
Zhang, R.;Zhang, Y.;Hou, J. G.
具有化学识别的单个分子的可视化是催化、分子纳米技术和生物技术的长期目标。分子振动为这种鉴定提供了有价值的“指纹”。基于尖端增强的拉曼散射的振动光谱学允许我们经由在尖端顶点处产生的强局部等离子体激元场（1-11）非常有效地访问分子种类的光谱信号。然而，尖端增强拉曼散射成像的最佳空间分辨率仍然限于3-15纳米（5，12 -16），这不足以化学地分辨单个分子。在这里，我们展示了拉曼光谱成像的空间分辨率低于一纳米，解决了一个单一的分子的内部结构和表面配置。这是通过将纳米腔等离子体激元的共振与分子电子振动跃迁（特别是负责发射拉曼光子的向下跃迁）进行光谱匹配来实现的。这种匹配是由扫描隧道显微镜提供的极其精确的调谐能力。实验证据表明，隧道间隙中的纳米腔等离子体激元场的高度受限和宽带性质对于通过产生用于拉曼激发和拉曼发射的有效双共振增强的超高分辨率成像是必不可少的。我们的技术不仅允许在单分子水平上进行化学成像，而且还提供了一种新的方法来研究单个分子的光学过程和光化学。
Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'finger-print' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex(1-11). However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres(5,12-16), which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.