非对称耦合纳米双棒近场光谱响应研究

Near-Field Spectral Characterization of Asymmetric Coupling Two Nanorods Structures

利用时域有限差分方法,研究了非对称纳米棒二聚体结构中不同端点局域等离激元(LSP)的近场响应。结果表明,长短棒中存在低频和高频两种模式,低频模式在处于两棒间隙端点处的场强显著强于外侧端点;高频模式在长棒间隙端点处的场强强于外侧端点,而短棒两端点的场强相同。借助不同纳米棒本征频率差异所对应的电荷库效应,很好地解释了不同位置的强度响应差异。对于不同端点的振荡频率,研究发现共振纳米棒两端点LSP振荡频率一致,非共振纳米棒两端点LSP振荡频率不同,并且在非共振棒中,位于两棒间隙位置处的端点的振荡频率,与共振纳米棒频率更接近。

The finite-difference time-domain method characterizes the near-field responses at different ends of the asymmetric nanorod structures.The results show that two modes exist in the long and short rods:low-frequency mode(LFM)and high-frequency mode(HFM).The field enhancement of the LFM at the gap end points is considerably higher than that at the outer end points.For HFM,the intensity at the gap end point of the long rod is stronger than that at the outer end point;however,the intensity at the two end points of the short rod is the same.The difference in the intensity response at different ends of two nanorods is attributed to the charge reservoir effect resulting from the different intrinsic frequencies of the nanorods.Furthermore,the oscillation frequencies of different end points are consistent at both ends of resonant nanorods and different at nonresonant nanorods.In addition,the oscillation frequency at the gap end point of the nonresonant nanorod is closer to that of the resonant frequency compared with the one at the outer point.