摘要
提出了一种新颖的非对称银纳米柱结构,并采用时域有限差分(FDTD)法对其激发的表面等离子体共振(SPR)模式进行了数值模拟。通过磁控溅射和离子束刻蚀技术,成功制备了该单层非对称银纳米柱结构,并通过透射光谱分析其光学特性。实验结果表明,该结构对环境折射率变化敏感,在生化物质的现场快速检测中显示出巨大潜力。基于这一发现,进一步设计并模拟了双层非对称银纳米柱结构,确认了其对偏振光的高度敏感性。这些研究成果为开发新型生物化学传感器提供了重要的理论和实验基础。
Objective Surface plasmons have attracted significant attention due to their broad applications in nanophotonics,biology,and spectroscopy.Among these,polarization-sensitive nanostructures are especially critical in biology and communications.Asymmetric structures,in particular,offer an effective means to achieve polarization-sensitive responses.While considerable research has focused on nanostructures,individual asymmetric nanostructures have not been studied as extensively.In this study,we investigate the optical properties of single asymmetric silver nanopillars,examining their polarization-dependent characteristics through both simulation and experimental methods.In addition,we introduce a double-layer asymmetric silver nanopillar structure,expanding the potential applications and functionality of these nanostructures.Methods We utilize the finite-difference time-domain(FDTD)method to simulate the transmission spectra of asymmetric silver nanopillar structures,evaluating the influence of various parameters on their optical properties.Specifically,we analyze the effects of variations in height,diameter,and tilt angles on the optical behavior of these nanopillars with results shown in Fig.5.Mode field analysis is conducted to explore the surface plasmon modes excited by these structures,as shown in Fig.4.The asymmetric silver nanopillar structures are fabricated on quartz substrates using magnetron sputtering for silver deposition,followed by ion beam etching.Submicron microsphere spin-coating is utilized as a masking technique,with details provided in Fig.7.Transmission spectroscopy is then employed to analyze the relationship between the optical properties and geometric parameters of the fabricated nanopillars,as shown in Fig.11.This analysis further investigates the potential application in environmental refractive index change sensing.Results and Discussions We provide details of the simulated transmission spectra of asymmetric silver nanopillar structures under varying periodic conditions,as shown in Fig.2.As the periodicity increases,the wavelength of the transmission trough shifts towards the red,attributed to surface lattice resonances(SLRs)induced by the ordered,large-area array structure of the silver nanopillars.Alterations in the array’s periodicity also influence the SLR troughs.Figure 5(c)shows the transmission spectra of asymmetric silver nanopillars under different polarization anglesα,with corresponding plan views shown in Fig.6(c).As the polarization angle increases,the transmission troughs at 478,658,and 900 nm exhibit redshifts,demonstrating pronounced polarization selectivity.The electric field at the 731 nm transmission trough results from the coupling between the surface plasmon resonance (SPR) mode generated by diffractionat the silver-air interface and the SLR surface plasmon between the asymmetric silver nanopillars. Notably, the enhancedelectric field at the 900 nm trough primarily occurs at the top of the asymmetric silver nanopillars at the air interface, wherethe incident light excites SPR. In contrast, at 1300 nm, the enhanced electric field primarily occurs at the bottom of theasymmetric silver nanopillars at the interface with the substrate, due to SPR excited by the incident light at the silver/silicainterface. When the diameter is increased to 600 and 700 nm, no shifts in the resonance wavelengths at 900 and 1300 nmare observed. Experimentally fabricated single-layer tilted silver nanopillars, with a spacing exceeding 1000 nm,demonstrate that as the polarization angle of incident light increases from 0° to 90° , the resonance wavelength of thetransmission spectrum at 678 nm shifts to 762 nm, and the intensity of the transmission spectrum correspondinglyincreases, indicating the high sensitivity of the asymmetric silver nanopillar structure to changes in the polarization angle ofthe incident light. In addition, the refractive index sensitivity of the structure at the 778 nm wavelength is measured to be258 nm/RIU. We also simulate a double-layer asymmetric silver nanopillar structure, as shown in Fig. 13. Thesimulations reveal that as the tilt angle δ between the layers of silver nanopillars increases, the response to polarized lightbecomes more sensitive, with the resonance wavelength shifting further towards longer wavelengths under differentpolarization angles of incident light. Compared to the single-layer structure, the double-layer asymmetric silver nanopillarstructure exhibits a more sensitive response to changes in the polarization angle of incident light, further affirming theadvantages of asymmetric nanostructures in enhancing localized near-field effects and reducing plasmonic resonance loss.These characteristics have significant implications for applications in optical sensing, optical communications, andpolarization modulation.Conclusions We outline the fabrication process of asymmetric silver nanopillar structures and employ numericalsimulations using the FDTD method to explore the surface plasmon modes and optical properties they excite. Single-layerasymmetric silver nanopillar structures are fabricated using magnetron sputtering for silver deposition and ion beam etching.Optical spectroscopy measurements demonstrate that these structures are sensitive to the polarization of incident light andchanges in environmental refractive indices, making them suitable for monitoring variations in environmental refractiveindices. They also show substantial potential for the rapid on-site detection of biochemical substances. In addition, adouble-layer asymmetric silver nanopillar structure is proposed. Simulation studies confirm that a larger angle between thetilt directions of the double-layer nanopillars leads to a more significant redshift of the resonance wavelength as thepolarization angle of the incident light increases, highlighting the enhanced sensitivity of these nanostructures to polarizedlight. The proposed double-layer asymmetric silver nanopillar structure is characterized by low cost, simplicity infabrication, and high repeatability, making it especially suitable for optical polarization control and promising for highsensitivitydetection of biomolecules.
作者
陈进
倪海彬
吴文杰
葛益娴
王婷婷
倪波
卢林林
常建华
Chen Jin;Ni Haibin;Wu Wenjie;Ge Yixian;Wang Tingting;Ni Bo;Lu Linlin;Chang Jianhua(School of Electronics and Information Engineering,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China;Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China)
出处
《光学学报》
CSCD
北大核心
2024年第22期210-219,共10页
Acta Optica Sinica
基金
国家自然科学基金(61605082,61875089)。
关键词
表面等离激元共振
非对称银纳米柱
折射率传感
surface plasmon resonance
asymmetric silver nanorod
refractive index sensing
