室温下金表面吸附分子的构象不均一性
Conformational heterogeneity of molecules physisorbed on a gold surface at room temperature
摘要：
由于暴露于空气中的分子的快速结构动力学，在室温下的定量单分子尖端增强拉曼光谱（TERS）研究仍然是一个挑战。在这里，我们展示了高光谱TERS成像的单个或几个灿烂的甲酚蓝（BCB）分子在室温下，随着定量光谱分析。通过使用薄Al $_{2}$ O $_{3}$覆盖层的定格方法实现了稳健的化学成像，该覆盖层抑制光谱扩散并抑制空气中的化学反应和污染。对于在TERS图像中空间分辨的分子，观察到高达7.5 cm $^{-1}$的清晰拉曼峰变化，这在分子系综中找不到。从密度泛函理论为基础的定量分析不同的TERS峰，我们揭示了在单分子水平上的构象异质性。这一工作为研究相互作用介质中的单分子性质提供了一种简便的方法，拓展了单分子振动光谱的研究范围。
英文摘要：
A quantitative single-molecule tip-enhanced Raman spectroscopy (TERS) study at room temperature remained a challenge due to the rapid structural dynamics of molecules exposed to air. Here, we demonstrate the hyperspectral TERS imaging of single or a few brilliant cresyl blue (BCB) molecules at room temperature, along with quantitative spectral analyses. Robust chemical imaging is enabled by the freeze-frame approach using a thin Al$_{2}$O$_{3}$ capping layer, which suppresses spectral diffusions and inhibits chemical reactions and contaminations in air. For the molecules resolved spatially in the TERS image, a clear Raman peak variation up to 7.5 cm$^{-1}$ is observed, which cannot be found in molecular ensembles. From density functional theory-based quantitative analyses of the varied TERS peaks, we reveal the conformational heterogeneity at the single-molecule level. This work provides a facile way to investigate the single-molecule properties in interacting media, expanding the scope of single-molecule vibrational spectroscopy studies.
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