The objective of this research is to take a comprehensive consideration of size, gap, and shape engineering, photonic design, and three-dimensional design to achieve the best surface enhanced Raman substrates for practical Raman based chemical and biological sensing applications. Engineering the optical properties of three dimensional metallic nanostructures helps one to gain a fundamental understanding of the plasmonic properties of those nanostructures, and bring innovative methods for applications such as SERS based sensors, metal enhanced fluorescence, plasmon propagation, etc.
Intellectual Merit: A finite-difference-time-domain method will be used to calculate local electric field distribution and optical properties of various metallic nanostructures in order to understand the contributions of different geometric factors and coupling, and to design optimal sensor substrates. The glancing angle deposition technique or oblique angle deposition technique combining with other sophisticated nanofabrication techniques will be used to fabricate and optimize the sensor substrates according to the theoretical results.
Broader Impacts: The successful development of a practical, simple, and inexpensive technique for fabrication of optimal surface enhanced Raman substrates with high sensitivity would not only lay a foundation for commercial development of practical Raman based sensors for biomedical diagnostics, national defense and security, but also have a large and immediate impact in the areas of nanostructure fabrication and engineering, fundamental surface science and analytical spectroscopy. In addition, this project will also establish a rigorous material physics, photonics, and nanotechnology education and training opportunity for graduate, undergraduate, and high school students.
The ultimate goal of this proposal is to take a comprehensive consideration of size and gap engineering, photonic design, and three-dimensional (3D) design to achieve the best surface enhanced Raman scattering (SERS) substrates for practical SERS based chemical and biological sensing applications. We have achieved this goal and extend our research on other 3D photonic structures. By fabricating and studying 3D silver nanorod arrays, including helical and zig-zag shapes, as well as porous nanorods, we explored their optical properties and SERS performances, and found that both zig-zag and porous nanorod arrays could give at least one order of magnitude higher SERS enhancement effect compared to the straight, solid nanorod counterparts. We have used a thin layer of SiO2 or Au to modify the Ag nanorod substrates, making them more stable for chemical sensing. In the meantime, we have developed a new fabrication method by combining glancing angle deposition and colloidal monolayer to fabricate large area, regular plasmonic nanostructures. Those nanostructures such as fan structure, oligomer structure, helically stacking plasmonic layer, or even Swiss-roll like nanostructures, have all shown strong circular dichroism properties and other plasmonic properties. Our preliminary studies have shown that those chiral structures can be used as a high sensitive sensor for chemical and biological applications. We have also extended this fabrication process for other materials, especially magnetic nano-materials. This project has resulted in a total of 20 peer reviewed journal publications, multiple conference presentations, and seminars. Some of the results have also been reported in the News Media. These results will have a profound impact on SERS based sensing and new photonic structure/material development. In the project period, we have trained a total of three graduate students, two international graduate students, three undergraduate students, and involved two high school teachers and one high school student. All the graduate students have received different honors, and three of them become faculty members or postdoc after receiving their PhD degrees. We also have fostered several national and international collaborations. Some of the results developed in this project have also been incorporated in the collegiate optics class taught by the Principle Investigator.
