使用聚焦离子束刻蚀的方法制备了不同间距的表面等离子结构阵列,研究了由方形和圆形所构成的阵列在不同间距下的光学反应.实验表明, 粒子之间耦合效应随着间距的显著减小而逐渐变强,从弱耦合变化为强耦合状态.当间距小于30nm时,发现耦合增强的反射效应,共振波长也会随着间距的减小而发生红移.将制备的超小间距纳米阵列和傅里叶变换光谱仪的ATR附件相耦合,实验验证了相关阵列结构在红外光谱增强方面的显著效果.相关的发现和表面等离子阵列结构可以在传感、探测和光谱增强等方面取得一定的应用.

Plasmonics paves the way for controlling electromagnetic waves at the nanoscale by coupling light to coherent electronic excitations(surface plasmon resonances, SPRs)at the interface between dielectric and metallic materials. Plasmonic resonances in metallic nanostructures have drawn increasing attention because of their extensive applications, including waveguides, microscopies, sensors, lasers, and light emitting diodes. The strong confinement of light associated with surface plasmon resonances can give rise to the fast development of different kinds of sub-wavelength photonic components and devices. The photon-electron excitations allow solid confinement of the electromagnetic waves to nanoscale dimensions which may lead to strong field enhancement. To manipulate the plasmonic resonances, diversified designs have been used to modify the features, sizes, and spacing of the metallic structures. In comparison with these physical approaches, varying the separations of optically functional nanoelements is a much more efficient method. Here, we investigate the optical response of plasmonic crystal arrays composed of square-and circle-shaped particles with different separations. Using focused ion beam milling, plasmonic crystal arrays with normal separation(relatively large size)are first fabricated, leading to weak coupling regime between adjacent particles. To minimize redeposition effects and achieve fine patterns, small beam current and parallel milling method are applied. In order to further generate plasmon-enhanced reflection, the separation between neighboring plasmonic crystals is remarkably decreased. As the separation reduces, the coupling effects become stronger, enabling strong coupling regime. It is found the reflection can be significantly enhanced by strong coupling effects and the resonance wavelength redshifts with decreasing separation when the gap size is smaller than 30nm. To verify the experimental results, finite-difference time-domain calculations are carried out. Simulations agree well with the measured data. By combining gold(Au)nanoparticle structures with ATR-FTIR spectroscopy technique, the absorbance of glucose can be effectively enhanced. The plasmonic crystal structures and new findings under investigation in this work may find extensive applications in chemical sensing, detecting and optical waveguiding.