高深宽比金属光栅制备及中红外波段传感特性

Fabrication and application of high aspect ratio metallic gratings for sensing in the mid-infrared region

利用纳米压印结合溅射和反应离子刻蚀工艺制备了具有高深宽比的金光栅,使用傅里叶变换红外光谱仪测得了反射谱线.测量结果显示,只在p偏振光垂直于光栅矢量方向入射条件下才存在共振反射峰,证明了"伪表面等离子体激元波"的存在.基于严格耦合波分析理论计算了金属光栅的反射率,研究了其作为中红外波段波长调制型表面等离子体共振传感器的可行性.数值计算表明负级次衍射光波对应的共振反射峰的移动能获得较高的波长灵敏度.对于深宽比为10的金光栅结构,+1级次和-3级次衍射光波对应的波长灵敏度分别为1600 nm/RIU和5000 nm/RIU,品质因子分别为20 RIU-1和60 RIU-1.

A method for fabricating high aspect ratio （HAR） metallic gratings using nanoimprint together with sputtering and reactive-ion etching （RIE） was introduced. The reflection spectrum is measured by Fourier transform infrared （ FT- IR） spectrometer in the mid-infrared （Mid-IR） region. The reflection peaks will appear just when the p-polarized light incident normally to the grating vector direction, which is very similar to the phenomenon of surface plasmon resonance. This is the so-called spoof surface plasmon resonance （SSPR）. Theoretical analysis based on rigorous coupled wave showed that spoof surface plasmon resonance is very sensitive to the change of refractive index in the surface of the metal. Thus this phenomenon has its potential use as a refractive index sensor. In addition, the shift of resonance wavelength with the refractive index of the metal surface is completely linear. The refractive index sensitivity of the Mid-IR SPR sensor are predicted to be 1600 nm per refractive index unit （ 1600 nm/RIU） and 5000 nm/RIU for the positive and negative order diffractive waves, respectively. The corresponding figure of merits of the whole system is predicted to be 20 RIU - and 60 RIU ^- 1, respectively. The list of applicable target materials will certainly expand greatly if mid-IR SPR-based sensors are developed.