AI 中文总结
研究分子与金属纳米间隙表面相互作用，引入等离子体增强非线性振动光谱，利用双共振纳米腔中同时的和频与差频产生，解析分子取向及优先吸附，发现非共振二阶非线性响应由分子与表面相互作用决定，提供强大分析工具。
AI 中文摘要
分子与表面的相互作用在许多研究和技术领域至关重要，涵盖从多相催化、聚合物科学到电化学等。金属纳米间隙在分子电子学和近场光谱学中具有特殊意义。由于这些双界面的隐蔽性，监测间隙内侧面特异性相互作用和相对分子取向的方法很少。本文引入等离子体增强非线性振动光谱作为研究金属纳米结内表面分子吸附的有效工具。通过利用双共振纳米腔中的同时振动和频与差频产生，我们以少数分子灵敏度解析了分子取向和对两个金表面之一的优先结合。我们还发现非共振（电子）二阶非线性响应并非金属表面的固有属性，而是由分子与表面的相互作用决定。我们的发现提供了一种强大的分析工具，借助市售中红外量子级联激光器，可轻松作为拉曼光谱的附加装置实现。
英文摘要
Molecule-surface interactions are central to many research and technological areas, spanning from heterogeneous catalysis and polymer science to electrochemistry. Of particular relevance are metallic nanogaps used in molecular electronics and near-field spectroscopy. Due to the buried nature of these double interfaces, few methods exist to monitor side-specific interactions and relative molecular orientation inside the gap. In this work, we introduce plasmon-enhanced nonlinear vibrational spectroscopy as an efficient tool to investigate surface molecular adsorption within metallic nanojunctions. By exploiting simultaneous vibrational sum- and difference-frequency generation in dual-resonant nanocavities, we resolve molecular orientation and preferential binding to one of the two gold surfaces, with few-molecule sensitivity. We also discover that the non-resonant (electronic) second-order nonlinear response is not an intrinsic property of the metal surface, but is instead governed by the molecule-surface interaction. Our findings provide a powerful analytical tool, easily implementable as an add-on to Raman spectroscopy, thanks to commercially available mid-infrared quantum cascade lasers.
