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Spectroscopy

C&EN 中文版

拉曼光谱，现拥有埃级分辨率

成像研究得出分子振动的原子分辨率图象

by Mitch Jacoby
April 11, 2019 | A version of this story appeared in Volume 97, Issue 15
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Most Popular in Analytical Chemistry

 

This set of three panels shows the molecule being studied and the simulated and measured vibrational images.
Credit: Nature
一个光谱方法选择性地映射出单个卟啉分子中的振动模式。此处所示模式（在中间进行模拟）主要涉及苯环（红色表示最高强度）。

请访问cenm.ag/chinese或关注ACS微信订阅号获取更多《化学与化工新闻》的中文内容

通过结合扫描探针显微镜，激光光谱和表面科学，研究者们将显微光谱的空间分辨率提升至埃级。研究展示了一个记录单个分子特定区域内振动光谱的方法，及一个用于捕捉该分子振动模式图象的技术 (Nature 2019, DOI: 10.1038/s41586-019-1059-9)。

拉曼光谱是探测分子振动的强大工具。它在商业上用于质量和过程控制，在科研中用于研究分子现象。但是，样例分子与光—通常为激光发出的可见光—相互作用所产生的拉曼信号是虚弱的，故限制了该方法的灵敏度。

40多年前，研究者们发现通过在粗糙金属表面吸附分析物分子可将拉曼信号增强一百万倍以上，如有微观的锋利尖刺的银。金属的尖刺好像天线，在纳米尺度的区域内扩大电磁场并增强信号。

This schematic depicts the interaction of the laser light, probe tip, and molecule under investigation.
Credit: Nature
通过扫描固定在铜表面的单个卟啉分子（CoTPP）的一个银尖，研究者可将分子振动模式成像。

找到这些纳米级热点并使分子对其吸附是棘手的。研究者们在扫描探针显微镜下使用超级锋利的金属尖点细致地将天线置于分子之上，这使研究者们快速地获得更多掌控力。通过针尖增强拉曼散射(TERS)，科学家们可记录来自针尖几个纳米内单个分子的拉曼光谱。

在这一新研究中，美国加利福尼亚大学欧文分校的Joonhee Lee 和V. Ara Apkarian与他们的研究伙伴们更进一步—他们使用四苯基钴卟啉作为测试用例，证实了针尖增强拉曼散射(TERS)可用于记录来自单个分子不同区域的特有光谱。当研究团队将针尖从一点，例如从一个苯环上—激发一个特定的C–H伸展—移动至分子的其他部分，在埃级分辨率下光谱有所不同。

“这真是个完美的工作，”美国明尼苏达大学明尼阿波利斯分校的激光光谱学家Renee Frontiera说。因为成像分辨率的限制，分子振动的具体方式通常依据理论而推得。而Apkarian的团队提出了一个在前所未有的空间分辨率上映射分子振动模式的方法。她补充道，“通过该工作，现在可以了解分子特定区域内聚积的能量是如何在整个结构中流动的。

Eric C. Le Ru是纳米尺度光学现象的一位专家，他对该研究也印象深刻。然而，他指出该研究中所用的专用真空设备和低温温度可能会限制该方法的适用性。此外，成功取决于卟啉与其所固定的铜表面所产生的强烈相互作用。其他分子和表面的组合或许不会获得同样的分辨率。

Frontiera对此认同。尽管如此，她说“我希望这些图片可在未来化学教材的振动光谱学章节中出现。”.

由YanYan为C&EN翻译为中文。原文（英文）点击此处。

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2024 American Chemical Society

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