SGER: Designing Active Nanostructures from Passive Metallic Films

Northwestern University, Evanston IL

Investigators

Abstract

TECHNICAL: This proposal describes fundamental studies of thin metallic films perforated with arrays of nanoscale holes. PI plans to investigate how a simple but revolutionary procedure to create structure on thin noble metal films can transform flat passive films into active nanostructures. Specifically, PI proposes to investigate how the size, shape, and arrangement of these small holes in noble metal films can play an active role in manipulating light. To characterize the properties of these nanostructured films, PI plans to measure the local and collective optical behavior of the same films. Therefore, complete near-field and far-field studies of metallic films of holes can be carried out to delineate among surface plasmon excitation, propagation and interference. The project integrates a new approach to fabricate nanohole arrays in thin metal films with sophisticated tools to characterize their optical properties. This combination allows PI to address the question of how surface plasmons can mediate enhanced transmission through hole arrays because PI can then correlate the near-field images of surface plasmons with their far-field spectra. Such local and collective studies on the same metallic films will enable PI to distinguish among surface plasmon polariton and localized surface plasmon excitation, propagation, and interference. Previous studies of subwavelength hole arrays have focused solely on their far-field properties and not on the underlying near-field phenomena, which is critical in the proposed mechanism for enhanced optical transmission. PI we will explore three inter-related but distinct ways that nanohole metallic films can function as active nanostructures. These strategies include: (i) manipulating SPs into standing wave patterns on films with arrays of widely spaced holes, (ii) enhancing and collimating the light transmission through arrays of closely spaced holes, and (iii) controlling the color and localized modes of light propagating through the films by changing the polarization. NON-TECHNICAL: Research will allow important contributions to be made not only for understanding how light is transmitted through the holes but will also enable one to design different structures in the metal films with potential to exhibit other interesting and unexpected optical properties. This work can provide insight into this decade-old problem as well as push forward other interesting phenomena in hole arrays besides surface plasmons, such as Wood's anomalies, diffraction, and waveguide modes. Outreach activities will concentrate primarily on the integration of research activities into the classroom and the development of content for 7-16 grade levels in the area of nanoscience and photonics. Specifically, a new research-based course for sophomores, sponsored by the NSFNUE program is being offered in Winter and Spring 2006. In addition, PI is contributing to the education and professional development of teachers in the NSF-Nanoscale Center for Learning and Teaching (NCLT).