Design And Fabrication Of Freestanding Plasmonic Nanoantennas And Their Application For Enhanced Raman Spectroscopy

Nanoantennas can focus and modulate light and electromagnetic fields in the wavelength range based on surface plasmon resonance.The optical nanoantenna with metallic nanogap can produce great field enhancement ef fect at its gap.It has been widely used in chemical and biological sensing,surface enhanced spectroscopy,molecular detection and other fields,among which the most typical application is the enhanced Raman spectroscopy in surface enhanced spectroscopy f ield.Compared with the plasmonic nanogaps on substrate,the suspended plasmonic structures has a better quality factor of local plasmon resonance and can obtain a better electromagnetic field enhancement effect.In order to fabricate the suspended plasmonic nanogap antennas,a variety of process methods have been developed.However,the suspended nanogaps realized by the lateral growth brought by metal deposition needs some experience to obtain good reliability and stability.The suspended nanoantenna realized by the sacrificial layer process can have reliable accuracy and controllable gap size,but there will be difficulties in processing,and it may need overlay process or subsequent etching.The process is relatively complex,and the nanoantennas may collapse during the release of the sacrificial layer.In this thesis,we aim to build a reliable suspended metallic nanogap antenna.We focus on the development of a reliable and simple processing method,combined wi th simulation and experimental tests to confirm its field enhancement effect,and the prepared metallic nanoantennas were applied to surface enhanced Raman scattering spectroscopy.The main research contents are as follows:(1)Different plasmon antenna were designed,and the local surface plasmon resonance and electric field enhancement characteristics were calculated and analyzed using the FDTD numerical simulation method.By comparing the antenna on the substrate with the suspended antenna,it is conclud ed that the suspended dimer can obtain a greater field enhancement effect.On this basis,the structural parameters of the suspended dimer were further studied,and the theoretical models of metallic nanoantennas with various sizes and spacings were establ ished.The influence of various parameters on the electric field enhancement of the nanoantennas was studied by adjusting different geometric parameters,finally the optimal design parameters of the suspended nanoantennas were obtained.(2)The fabrication process of suspended nanogap antenna was studied.The isolation layer was prepared by using surface treatment techniques including atomic layer deposition of alumina,oxygen plasma treatment and UV-Ozone treatment,so as to realize the bilayer resist process and complete reliable processing.By analyzing the reasons for the failure of the experiment,the experiment was iteratively improved,and finally a process flow that can stably process the suspended nanogap antenna was obtained.(3)The formation principle of ultra-thin layer was explored.The use of UV-Ozone treatment to HSQ can achieve the purpose of the process.The principle of surface modification was analyzed and discussed,and the bonding situation was analyzed by XPS analysis to determine its composition,so as to determine the basis of its modification.(4)Raman spectrum enhancement application of the processed nanoantennas was verified.The prepared nanoantennas were used in Raman spectroscopy test,and the Raman enhancement effect brought by the prepared suspended nanoantenna and the nanoantenna of the same size placed on the substrate were compared.It was verified that the prepared suspended metallic nanoantenna can bring a better Raman enhancement effect than the nanoantenna on the substrate,and the scattering peak height can reach 2.82 times that of the nanoantenna on the substrate.