金纳米柱阵列表面等离子体激元与J-聚集分子强耦合作用

Strong coupling between J-aggregates and surface plasmon polaritons in gold nanodisks arrays

采用脱模工艺制备了表面光滑的金纳米柱阵列结构,这种加工方法操作简单、可重复性强,可以将形貌相同的纳米柱阵列结构大批量复制到不同衬底上.采用这种金纳米柱阵列结构激发表面等离子体激元并实现了其与J-聚集染料分子的强耦合作用.在所制备的杂化耦合体系中,观测到了200 meV的拉比劈裂值.进一步通过调节金纳米柱阵列的周期来改变耦合强度,在反射谱中观测到了强耦合存在的标志性实验证据:耦合杂化态对应能量的反交叉曲线.这种简单并可以大批量制备的强耦合杂化体系对于促进强耦合作用在纳米等离子体器件中的广泛应用具有积极意义.

Recently, much attention has been paid to an interesting subject, i.e., the interactions between surface plasmon polaritons（SPPs） and molecules. The interactions between SPPs and molecules often appear in two opposite cases,namely weak and strong coupling. When the interaction is weak, the absorption maximum simply coincides with the electronic transition energy of the molecule. In the weak coupling regime, the wave functions of the molecule and the SPP modes are considered to be unperturbed, only leading to enhancement of the absorption or fluorescence of the molecules. On the other hand, when the interaction is strong enough, the SPPs and molecules can form a coherent hybrid object, thus the excitation energy is shared by and oscillates between the SPPs and molecular systems（Rabi oscillations）, leading to vacuum Rabi splitting of energy levels at the resonance frequency. Due to the fact that both the SPPs and the molecule components can be confined into the nanometer scale, the work on strong coupling with SPPs offers a very good opportunity to realize nanoplasmonic devices, such as thresholdless laser and room temperature B-E condensates.In this work, we investigate a hybrid system formed by strong coupled gold nanodisk arrays and J-aggregate molecules. Smooth gold nanodisk arrays are fabricated by a template-stripping process. In such an experimentally simple replicate process, mass-production of gold nanodisk arrays with the same morphology can be transferred from patterned indium tin oxides（ITO） glass. The structures on ITO glass are milled with a focused ion beam. Periodic gold nanodisk arrays have the capability of converting light into SPPs modes, resulting in a significant field confinement at the patterned metal surface. In particular, the desired SPP mode can be chosen by changing the nanodisk array period to match the absorbance peak of the J-aggregate molecule. On the other hand, J-aggregate molecule is chosen due to its large dipole moments and absorption coefficient, which makes it attractive for designing the strong exciton-plasmon interaction system. The strong coupled system is formed when the J-aggregate molecule is spin-coated on the gold nanodisk arrays. Through reflection measurements, Rabi splitting energy value 200 meV is observed when the period of the nanodisk array is 350 nm. Through tuning the coupling strength by changing the lattice period from 250 nm to 450 nm, the typical signature of strong coupling： anticrossing of energies is found in reflection spectra. This simple replicate process for strong coupling hybrid system fabrication should play an important role in designing novel ultrafast nanoplasmonic devices with coherent functionalities.