Brawley Zachary T, Storm S David, Contreras Mora Diego A, Pelton Matthew, Sheldon Matthew
Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77840, USA.
Department of Physics, UMBC (University of Maryland, Baltimore County), Baltimore, Maryland 21250, USA.
J Chem Phys. 2021 Mar 14;154(10):104305. doi: 10.1063/5.0039195.
Vibrational strong coupling of molecules to optical cavities based on plasmonic resonances has been explored recently because plasmonic near-fields can provide strong coupling in sub-diffraction limited volumes. Such field localization maximizes coupling strength, which is crucial for modifying the vibrational response of molecules and, thereby, manipulating chemical reactions. Here, we demonstrate an angle-independent plasmonic nanodisk substrate that overcomes limitations of traditional Fabry-Pérot optical cavities because the design can strongly couple with all molecules on the surface of the substrate regardless of molecular orientation. We demonstrate that the plasmonic substrate provides strong coupling with the C=O vibrational stretch of deposited films of PMMA. We also show that the large linewidths of the plasmon resonance allow for simultaneous strong coupling to two, orthogonal water symmetric and asymmetric vibrational modes in a thin film of copper sulfate monohydrate deposited on the substrate surface. A three-coupled-oscillator model is developed to analyze the coupling strength of the plasmon resonance with these two water modes. With precise control over the nanodisk diameter, the plasmon resonance is tuned systematically through the modes, with the Rabi splitting from both modes varying as a function of the plasmon frequency and with strong coupling to both modes achieved simultaneously for a range of diameters. This work may aid further studies into manipulation of the ground-state chemical landscape of molecules by perturbing multiple vibrational modes simultaneously and increasing the coupling strength in sub-diffraction limited volumes.
基于等离子体共振的分子与光学腔的振动强耦合最近已被探索，因为等离子体近场可以在亚衍射极限体积内提供强耦合。这种场局域化使耦合强度最大化，这对于改变分子的振动响应从而操纵化学反应至关重要。在这里，我们展示了一种与角度无关的等离子体纳米盘衬底，它克服了传统法布里 - 珀罗光学腔的局限性，因为该设计可以与衬底表面上的所有分子强烈耦合，而与分子取向无关。我们证明了该等离子体衬底与聚甲基丙烯酸甲酯（PMMA）沉积膜的C = O振动拉伸提供了强耦合。我们还表明，等离子体共振的大线宽允许与沉积在衬底表面的一水合硫酸铜薄膜中的两种正交的水对称和非对称振动模式同时实现强耦合。开发了一个三耦合振荡器模型来分析等离子体共振与这两种水模式的耦合强度。通过对纳米盘直径的精确控制，等离子体共振通过这些模式进行系统调谐，两种模式的拉比分裂随等离子体频率变化，并且对于一系列直径同时实现了与两种模式的强耦合。这项工作可能有助于进一步研究通过同时扰动多个振动模式并在亚衍射极限体积内增加耦合强度来操纵分子的基态化学态势。
